U.S. Supreme Court Illinois v. Gates, 462
U.S. 213 (1983) Illinois v. Gates No. 81-430 Argued October 13,
1982 Reargued March 1,
1983 Decided June 8, 1983 462
U.S. 213 CERTIORARI TO THE SUPREME COURT OF
ILLINOIS Syllabus On May 3, 1978, the Police Department of Bloomingdale, Ill.,
received an anonymous letter which included statements that
respondents, husband and wife, were engaged in selling drugs; that
the wife would drive their car to Florida on May 3 to be loaded
with drugs, and the husband would fly down in a few days to drive
the car back; that the car's trunk would be loaded with drugs; and
that respondents presently had over $100,000 worth of drugs in
their basement. Acting on the tip, a police officer determined
respondents' address and learned that the husband made a
reservation on a May 5 flight to Florida. Arrangements for
surveillance of the flight were made with an agent of the Drug
Enforcement Administration (DEA), and the surveillance disclosed
that the husband took the flight, stayed overnight in a motel room
registered in the wife's name, and left the following morning with
a woman in a car bearing an Illinois license plate issued to the
husband, heading north on an interstate highway used by travelers
to the Bloomingdale area. A search warrant for respondents'
residence and automobile was then obtained from an Illinois state
court judge, based on the Bloomingdale police officer's affidavit
setting forth the foregoing facts and a copy of the anonymous
letter. When respondents arrived at their home, the police were
waiting, and discovered marihuana and other contraband in
respondents' car trunk and home. Prior to respondents' trial on
charges of violating state drug laws, the trial court ordered
suppression of all the items seized, and the Illinois Appellate
Court affirmed. The Illinois Supreme Court also affirmed, holding
that the letter and affidavit were inadequate to sustain a
determination of probable cause for issuance of the search warrant
under Aguilar v. Texas, 378 U. S. 108 , and Spinelli v. United States, 393 U.
S. 410 , since they failed to satisfy the "two-pronged
test" of (1) revealing the informant's "basis of knowledge" and (2)
providing sufficient facts to establish either the informant's
"veracity" or the "reliability" of the informant's report. Held: 1. The question -- which this Court requested the parties to
address -- whether the rule requiring the exclusion at a criminal
trial of evidence obtained in violation of the Fourth Amendment
should be modified so as, for example, not to require exclusion of
evidence obtained in the reasonable Page 462 U. S. 214 belief that the search and seizure at issue was consistent with
the Fourth Amendment, will not be decided in this case, since it
was not presented to or decided by the Illinois courts. Although
prior decisions interpreting the "not pressed or passed on below"
rule have not involved a State's failure to raise a defense to a
federal right or remedy asserted below, the purposes underlying the
rule are, for the most part, as applicable in such a case as in one
where a party fails to assert a federal right. The fact that the
Illinois courts affirmatively applied the federal exclusionary rule
does not affect the application of the "not pressed or passed on
below" rule. Nor does the State's repeated opposition to
respondents' substantive Fourth Amendment claims suffice to have
raised the separate question whether the exclusionary rule should
be modified. The extent of the continued vitality of the rule is an
issue of unusual significance, and adhering scrupulously to the
customary limitations on this Court's discretion promotes respect
for its adjudicatory process and the stability of its decisions,
and lessens the threat of untoward practical ramifications not
foreseen at the time of decision. Pp. 462 U. S.
217 -224.

															2. The rigid "two-pronged test" under Aguilar and Spinelli for determining whether an informant's tip
establishes probable cause for issuance of a warrant is abandoned,
and the "totality of the circumstances" approach that traditionally
has informed probable cause determinations is substituted in its
place. The elements under the "two-pronged test" concerning the
informant's "veracity," "reliability," and "basis of knowledge"
should be understood simply as closely intertwined issues that may
usefully illuminate the common sense, practical question whether
there is "probable cause" to believe that contraband or evidence is
located in a particular place. The task of the issuing magistrate
is simply to make a practical, common sense decision whether, given
all the circumstances set forth in the affidavit before him, there
is a fair probability that contraband or evidence of a crime will
be found in a particular place. And the duty of a reviewing court
is simply to ensure that the magistrate had a substantial basis for
concluding that probable cause existed. This flexible, easily
applied standard will better achieve the accommodation of public
and private interests that the Fourth Amendment requires than does
the approach that has developed from Aguilar and Spinelli. Pp. 462 U. S.
230 -241.

															3. The judge issuing the warrant had a substantial basis for
concluding that probable cause to search respondents' home and car
existed. Under the "totality of the circumstances" analysis,
corroboration of details of an informant's tip by independent
police work is of significant value. Cf. Draper v. United
States, 358 U. S. 307 .
Here, even standing alone, the facts obtained through the
independent investigation of the Bloomingdale police officer and
the DEA at least suggested that Page 462 U. S. 215 respondents were involved in drug trafficking. In addition, the
judge could rely on the anonymous letter, which had been
corroborated in major part by the police officer's efforts. Pp. 462 U. S.
241 -246. 85 Ill. 2d
376 , 423 N.E.2d
887 , reversed.

															REHNQUIST, J., delivered the opinion of the Court, in which
BURGER, C.J., and BLACKMUN, POWELL, and O'CONNOR, JJ., joined.
WHITE, J., filed an opinion concurring in the judgment, post, p. 462 U. S. 246 .
BRENNAN, J., filed a dissenting opinion, in which MARSHALL, J.,
joined, post, p. 462 U. S. 274 .
STEVENS, J., filed a dissenting opinion, in which BRENNAN, J.,
joined, post, p. 462 U. S.
291 . Page 462 U. S. 216 JUSTICE REHNQUIST delivered the opinion of the Court.

															Respondents Lance and Susan Gates were indicted for violation of
state drug laws after police officers, executing a search warrant,
discovered marihuana and other contraband in their automobile and
home. Prior to trial, the Gateses moved to suppress evidence seized
during this search. The Illinois Supreme Court affirmed the
decisions of lower state courts granting the motion. 85 Ill. 2d
376 , 423 N.E.2d
887 (1981). It held that the affidavit submitted in support of
the State's application for a warrant to search the Gateses'
property Page 462 U. S. 217 was inadequate under this Court's decisions in Aguilar v.
Texas, 378 U. S. 108 (1964), and Spinelli v. United States, 393 U.
S. 410 (1969).

															We granted certiorari to consider the application of the Fourth
Amendment to a magistrate's issuance of a search warrant on the
basis of a partially corroborated anonymous informant's tip. 454
U.S. 1140 (1982). After receiving briefs and hearing oral argument
on this question, however, we requested the parties to address an
additional question:

															"[W]hether the rule requiring the exclusion at a criminal trial
of evidence obtained in violation of the Fourth Amendment, Mapp
v. Ohio, 367 U. S. 643 (1961); Weeks
v. United States, 232 U. S. 383 (1914), should to
any extent be modified, so as, for example, not to require the
exclusion of evidence obtained in the reasonable belief that the
search and seizure at issue was consistent with the Fourth
Amendment." 459 U.S.
1028 (1982).

															We decide today, with apologies to all, that the issue we framed
for the parties was not presented to the Illinois courts and,
accordingly, do not address it. Rather, we consider the question
originally presented in the petition for certiorari, and conclude
that the Illinois Supreme Court read the requirements of our Fourth
Amendment decisions too restrictively. Initially, however, we set
forth our reasons for not addressing the question regarding
modification of the exclusionary rule framed in our order of
November 29, 1982. Ibid. I Our certiorari jurisdiction over decisions from state courts
derives from 28 U.S.C. § 1257, which provides that

															"[f]inal judgments or decrees rendered by the highest court of a
State in which a decision could be had, may be reviewed by the
Supreme Court as follows: . . . (3) By writ of certiorari, . . .
where any title, right, privilege or immunity is specially set up
or claimed under the Constitution, treaties or statutes Page 462 U. S. 218 of . . . the United States."

															The provision derives, albeit with important alterations, see, e.g., Act of Dec. 23, 1914, ch. 2, 38 Stat. 790; Act
of June 25, 1948, § 1257, 62 Stat. 929, from the Judiciary Act of
1789, § 25, 1 Stat. 85.

															Although we have spoken frequently on the meaning of § 1257 and
its predecessors, our decisions are in some respects not entirely
clear. We held early on that § 25 of the Judiciary Act of 1789
furnished us with no jurisdiction unless a federal question had
been both raised and decided in the state court below. As Justice
Story wrote in Crowell v.
Randell , 10 Pet. 368, 35 U. S. 392 (1836): "If both of these requirements do not appear on the record,
the appellate jurisdiction fails." See
also Owings v.
Norwood's Lessee , 5 Cranch 344 (1809). [ Footnote 1 ]

															More recently, in McGoldrick v. Compagnie Generale
Transatlantique, 309 U. S. 430 , 309 U. S.
434 -435 (1940), the Court observed:

															"But it is also the settled practice of this Court, in the
exercise of its appellate jurisdiction, that it is only in
exceptional cases, and then only in cases coming from the federal
courts, that it considers questions urged by a petitioner or
appellant not pressed or passed upon in the courts below. . . . In
cases coming here from state courts in which a state statute is
assailed as unconstitutional, there are reasons of peculiar force
which should lead us to refrain from deciding questions not
presented or decided in the highest court of the state whose
judicial action we are called upon to review. Apart from the Page 462 U. S. 219 reluctance with which every court should proceed to set aside
legislation as unconstitutional on grounds not properly presented,
due regard for the appropriate relationship of this Court to state
courts requires us to decline to consider and decide questions
affecting the validity of state statutes not urged or considered
there. It is for these reasons that this Court, where the
constitutionality of a statute has been upheld in the state court,
consistently refuses to consider any grounds of attack not raised
or decided in that court."

															Finally, the Court seemed to reaffirm the jurisdictional
character of the rule against our deciding claims "not pressed nor
passed upon" in state court in State Farm Mutual Automobile
Ins. Co. v. Duel, 324 U. S. 154 , 324 U. S. 160 (1945), where we explained that, "[s]ince the [State] Supreme Court
did not pass on the question, we may not do so." See also Hill
v. California, 401 U. S. 797 , 401 U. S.
805 -806 (1971).

															Notwithstanding these decisions, however, several of our more
recent cases have treated the so-called "not pressed or passed upon
below" rule as merely a prudential restriction. In Terminiello
v. Chicago, 337 U. S. 1 (1949),
the Court reversed a state criminal conviction on a ground not
urged in state court, nor even in this Court. Likewise, in Vachon v. New Hampshire, 414 U. S. 478 (1974), the Court summarily reversed a state criminal conviction on
the ground, not raised in state court, or here, that it had been
obtained in violation of the Due Process Clause of the Fourteenth
Amendment. The Court indicated in a footnote, id. at 414 U. S. 479 ,
n. 3, that it possessed discretion to ignore the failure to raise
in state court the question on which it decided the case.

															In addition to this lack of clarity as to the character of the
"not pressed or passed upon below" rule, we have recognized that it
often may be unclear whether the particular federal question
presented in this Court was raised or passed upon below. In Dewey v. Des Moines, 173 U. S. 193 , 173 U. S.
197 -198 (1899), the fullest treatment of the subject,
the Court said Page 462 U. S. 220 that,

															"[i]f the question were only an enlargement of the one mentioned
in the assignment of errors, or if it were so connected with it in
substance as to form but another ground or reason for alleging the
invalidity of the [lower court's] judgment, we should have no
hesitation in holding the assignment sufficient to permit the
question to be now raised and argued. Parties are not confined here
to the same arguments which were advanced in the courts below upon
a Federal question there discussed. [ Footnote 2 ]"

															We have not attempted, and likely would not have been able, to
draw a clear-cut line between cases involving only an "enlargement"
of questions presented below and those involving entirely new
questions.

															The application of these principles in the instant case is not
entirely straightforward. It is clear in this case that respondents
expressly raised, at every level of the Illinois judicial system,
the claim that the Fourth Amendment had been violated by the
actions of the Illinois police and that the evidence seized by the
officers should be excluded from their trial. It also is clear that
the State challenged, at every level of the Illinois court system,
respondents' claim that the substantive requirements of the Fourth
Amendment had been violated. The State never, however, raised or
addressed the question whether the federal exclusionary rule should
be modified in any respect, and none of the opinions of the Page 462 U. S. 221 Illinois courts give any indication that the question was
considered.

															The case, of course, is before us on the State's petition for a
writ of certiorari. Since the Act of Dec. 23, 1914, ch. 2, 38 Stat.
790, jurisdiction has been vested in this Court to review state
court decisions even when a claimed federal right has been upheld.
Our prior decisions interpreting the "not pressed or passed on
below" rule have not, however, involved a State's failure to raise
a defense to a federal right or remedy asserted below. As explained
below, however, we can see no reason to treat the State's failure
to have challenged an asserted federal claim differently from the
failure of the proponent of a federal claim to have raised that
claim.

															We have identified several purposes underlying the "not pressed
or passed upon" rule: for the most part, these are as applicable to
the State's failure to have opposed the assertion of a particular
federal right as to a party's failure to have asserted the claim.
First, "[q]uestions not raised below are those on which the record
is very likely to be inadequate, since it certainly was not
compiled with those questions in mind." Cardinale v.
Louisiana, 394 U. S. 437 , 394 U. S. 439 (1969). Exactly the same difficulty exists when the State urges
modification of an existing constitutional right or accompanying
remedy. Here, for example, the record contains little, if anything,
regarding the subjective good faith of the police officers that
searched the Gateses' property -- which might well be an important
consideration in determining whether to fashion a good faith
exception to the exclusionary rule. Our consideration of whether to
modify the exclusionary rule plainly would benefit from a record
containing such facts.

															Likewise, "due regard for the appropriate relationship of this
Court to state courts," McGoldrick v. Compagnie Generale
Transatlantique, 309 U.S. at 309 U. S.
434 -435, demands that those courts be given an
opportunity to consider the constitutionality of the actions of
state officials, and, equally important, proposed changes in
existing remedies for unconstitutional Page 462 U. S. 222 actions. Finally, by requiring that the State first argue to the
state courts that the federal exclusionary rule should be modified,
we permit a state court, even if it agrees with the State as a
matter of federal law, to rest its decision on an adequate and
independent state ground. See Cardinale, supra, at 394 U. S. 439 .
Illinois, for example, adopted an exclusionary rule as early as
1923, see People v. Brocamp, 307 Ill. 448, 138 N.E. 728
(1923), and might adhere to its view even if it thought we would
conclude that the federal rule should be modified. In short, the
reasons supporting our refusal to hear federal claims not raised in
state court apply with equal force to the State's failure to
challenge the availability of a well-settled federal remedy.
Whether the "not pressed or passed upon below" rule is
jurisdictional, as our earlier decisions indicate, see
supra at 462 U. S.
217 -219, or prudential, as several of our later
decisions assume, or whether its character might be different in
cases like this from its character elsewhere, we need not decide.
Whatever the character of the rule may be, consideration of the
question presented in our order of November 29, 1982, would be
contrary to the sound justifications for the "not pressed or passed
upon below" rule, and we thus decide not to pass on the issue.

															The fact that the Illinois courts affirmatively applied the
federal exclusionary rule -- suppressing evidence against
respondents -- does not affect our conclusion. In Morrison v.
Watson, 154 U. S. 111 (1894), the Court was asked to consider whether a state statute
impaired the plaintiff in error's contract with the defendant in
error. It declined to hear the case because the question presented
here had not been pressed or passed on below. The Court
acknowledged that the lower court's opinion had restated the
conclusion, set forth in an earlier decision of that court, that
the state statute did not impermissibly impair contractual
obligations. Nonetheless, it held that there was no showing that
"there was any real contest at any stage of this case upon the
point," id. at 154 U. S. 115 ,
and that without such a contest, the routine restatement Page 462 U. S. 223 and application of settled law by an appellate court did not
satisfy the "not pressed or passed upon below" rule. Similarly, in
the present case, although the Illinois courts applied the federal
exclusionary rule, there was never "any real contest" upon the
point. The application of the exclusionary rule was merely a
routine act, once a violation of the Fourth Amendment had been
found, and not the considered judgment of the Illinois courts on
the question whether application of a modified rule would be
warranted on the facts of this case. In such circumstances, absent
the adversarial dispute necessary to apprise the state court of the
arguments for not applying the exclusionary rule, we will not
consider the question whether the exclusionary rule should be
modified.

															Likewise, we do not believe that the State's repeated opposition
to respondents' substantive Fourth Amendment claims suffices to
have raised the question whether the exclusionary rule should be
modified. The exclusionary rule is "a judicially created remedy
designed to safeguard Fourth Amendment rights generally," and not
"a personal constitutional right of the party aggrieved." United States v. Calandra, 414 U.
S. 338 , 414 U. S. 348 (1974). The question whether the exclusionary rule's remedy is
appropriate in a particular context has long been regarded as an
issue separate from the question whether the Fourth Amendment
rights of the party seeking to invoke the rule were violated by
police conduct. See, e.g., United States v. Havens, 446 U. S. 620 (1980); United States v. Ceccolini, 435 U.
S. 268 (1978); United States v. Calandra, supra;
Stone v. Powell, 428 U. S. 465 (1976). Because of this distinction, we cannot say that
modification or abolition of the exclusionary rule is "so connected
with [the substantive Fourth Amendment right at issue] as to form
but another ground or reason for alleging the invalidity" of the
judgment. Dewey v. Des Moines, 173 U.S. at 173 U. S.
197 -198. Rather, the rule's modification was, for
purposes of the "not pressed or passed upon below" rule, a separate
claim that had to be specifically presented to the state
courts. Page 462 U. S. 224 Finally, weighty prudential considerations militate against our
considering the question presented in our order of November 29,
1982. The extent of the continued vitality of the rules that have
developed from our decisions in Weeks v. United States, 232 U. S. 383 (1914), and Mapp v. Ohio, 367 U.
S. 643 (1961), is an issue of unusual significance.
Sufficient evidence of this lies just in the comments on the issue
that Members of this Court recently have made, e.g., Bivens v.
Six Unknown Fed. Narcotics Agents, 403 U.
S. 388 , 403 U. S. 415 (1971) (BURGER, C.J., dissenting); Coolidge v. New
Hampshire, 403 U. S. 443 , 403 U. S. 490 (1971) (Harlan, J., concurring); id. at 403 U. S. 502 (Black, J., dissenting); Stone v. Powell, supra, at 428 U. S.
537 -539 (WHITE, J., dissenting); Brewer v.
Williams, 430 U. S. 387 , 430 U. S.
413 -414 (1977) (POWELL, J., concurring); Robbins v.
California, 453 U. S. 420 , 453 U. S. 437 , 453 U. S.
443 -444 (1981) (REHNQUIST, J., dissenting). Where
difficult issues of great public importance are involved, there are
strong reasons to adhere scrupulously to the customary limitations
on our discretion. By doing so, we "promote respect . . . for the
Court's adjudicatory process [and] the stability of [our]
decisions." Mapp v. Ohio, 367 U.S. at 367 U. S. 677 (Harlan, J., dissenting). Moreover, fidelity to the rule guarantees
that a factual record will be available to us, thereby discouraging
the framing of broad rules, seemingly sensible on one set of facts,
which may prove ill-considered in other circumstances. In Justice
Harlan's words, adherence to the rule lessens the threat of
"untoward practical ramifications," id. at 367 U. S. 676 (dissenting opinion), not foreseen at the time of decision. The
public importance of our decisions in Weeks and Mapp and the emotions engendered by the debate surrounding
these decisions counsel that we meticulously observe our customary
procedural rules. By following this course, we promote respect for
the procedures by which our decisions are rendered, as well as
confidence in the stability of prior decisions. A wise exercise of
the powers confided in this Court dictates that we reserve for
another day the question whether the exclusionary rule should be
modified. Page 462 U. S. 225 II We now turn to the question presented in the State's original
petition for certiorari, which requires us to decide whether
respondents' rights under the Fourth and Fourteenth Amendments were
violated by the search of their car and house. A chronological
statement of events usefully introduces the issues at stake.
Bloomingdale, Ill., is a suburb of Chicago located in Du Page
County. On May 3, 1978, the Bloomingdale Police Department received
by mail an anonymous handwritten letter which read as follows:

															"This letter is to inform you that you have a couple in your
town who strictly make their living on selling drugs. They are Sue
and Lance Gates, they live on Greenway, off Bloomingdale Rd. in the
condominiums. Most of their buys are done in Florida. Sue his wife
drives their car to Florida, where she leaves it to be loaded up
with drugs, then Lance flys down and drives it back. Sue flys back
after she drops the car off in Florida. May 3 she is driving down
there again and Lance will be flying down in a few days to drive it
back. At the time Lance drives the car back he has the trunk loaded
with over $100,000.00 in drugs. Presently they have over
$100,000.00 worth of drugs in their basement."

															"They brag about the fact they never have to work, and make
their entire living on pushers."

															"I guarantee if you watch them carefully you will make a big
catch. They are friends with some big drugs dealers, who visit
their house often."

															"Lance & Susan Gates"

															"Greenway"

															"in Condominiums"

															The letter was referred by the Chief of Police of the
Bloomingdale Police Department to Detective Mader, who decided to
pursue the tip. Mader learned, from the office of the Illinois
Secretary of State, that an Illinois driver's license had Page 462 U. S. 226 been issued to one Lance Gates, residing at a stated address in
Bloomingdale. He contacted a confidential informant, whose
examination of certain financial records revealed a more recent
address for the Gateses, and he also learned from a police officer
assigned to O'Hare Airport that "L. Gates" had made a reservation
on Eastern Airlines Flight 245 to West Palm Beach, Fla., scheduled
to depart from Chicago on May 5 at 4:15 p. m.

															Mader then made arrangements with an agent of the Drug
Enforcement Administration for surveillance of the May 5 Eastern
Airlines flight. The agent later reported to Mader that Gates had
boarded the flight, and that federal agents in Florida had observed
him arrive in West Palm Beach and take a taxi to the nearby Holiday
Inn. They also reported that Gates went to a room registered to one
Susan Gates and that, at 7 o'clock the next morning, Gates and an
unidentified woman left the motel in a Mercury bearing Illinois
license plates and drove north-bound on an interstate highway
frequently used by travelers to the Chicago area. In addition, the
DEA agent informed Mader that the license plate number on the
Mercury was registered to a Hornet station wagon owned by Gates.
The agent also advised Mader that the driving time between West
Palm Beach and Bloomingdale was approximately 22 to 24 hours.

															Mader signed an affidavit setting forth the foregoing facts, and
submitted it to a judge of the Circuit Court of Du Page County,
together with a copy of the anonymous letter. The judge of that
court thereupon issued a search warrant for the Gateses' residence
and for their automobile. The judge, in deciding to issue the
warrant, could have determined that the modus operandi of
the Gateses had been substantially corroborated. As the anonymous
letter predicted, Lance Gates had flown from Chicago to West Palm
Beach late in the afternoon of May 5th, had checked into a hotel
room registered in the name of his wife, and, at 7 o'clock the
following morning, had headed north, accompanied by an unidentified
woman, Page 462 U. S. 227 out of West Palm Beach on an interstate highway used by
travelers from South Florida to Chicago in an automobile bearing a
license plate issued to him.

															At 5:15 a.m. on March 7, only 36 hours after he had flown out of
Chicago, Lance Gates, and his wife, returned to their home in
Bloomingdale, driving the car in which they had left West Palm
Beach some 22 hours earlier. The Bloomingdale police were awaiting
them, searched the trunk of the Mercury, and uncovered
approximately 350 pounds of marihuana. A search of the Gateses'
home revealed marihuana, weapons, and other contraband. The
Illinois Circuit Court ordered suppression of all these items, on
the ground that the affidavit submitted to the Circuit Judge failed
to support the necessary determination of probable cause to believe
that the Gateses' automobile and home contained the contraband in
question. This decision was affirmed in turn by the Illinois
Appellate Court, 82 Ill.App.3d 749, 403 N.E.2d 77 (1980), and by a
divided vote of the Supreme Court of Illinois. 85 Ill. 2d
376 , 423 N.E.2d
887 (1981).

															The Illinois Supreme Court concluded -- and we are inclined to
agree -- that, standing alone, the anonymous letter sent to the
Bloomingdale Police Department would not provide the basis for a
magistrate's determination that there was probable cause to believe
contraband would be found in the Gateses' car and home. The letter
provides virtually nothing from which one might conclude that its
author is either honest or his information reliable; likewise, the
letter gives absolutely no indication of the basis for the writer's
predictions regarding the Gateses' criminal activities. Something
more was required, then, before a magistrate could conclude that
there was probable cause to believe that contraband would be found
in the Gateses' home and car. See Aguilar v. Texas, 378
U.S. at 378 U. S. 109 ,
n. 1; Nathanson v. United States, 290 U. S.
41 (1933).

															The Illinois Supreme Court also properly recognized that
Detective Mader's affidavit might be capable of supplementing Page 462 U. S. 228 the anonymous letter with information sufficient to permit a
determination of probable cause. See Whiteley v. Warden, 401 U. S. 560 , 401 U. S. 567 (1971). In holding that the affidavit in fact did not contain
sufficient additional information to sustain a determination of
probable cause, the Illinois court applied a "two-pronged test,"
derived from our decision in Spinelli v. United States, 393 U. S. 410 (1969). [ Footnote 3 ] The
Illinois Supreme Court, like some others, apparently understood Spinelli as requiring that the anonymous letter satisfy
each of two independent requirements before it could be relied on.
85 Ill. 2d at 383, 423 N.E.2d at 890. According to this view, the
letter, as supplemented by Mader's affidavit, first had to
adequately reveal the "basis of knowledge" of the letterwriter --
the particular means by which he came by the information given in
his report. Second, it had to provide Page 462 U. S. 229 facts sufficiently establishing either the "veracity" of the
affiant's informant, or, alternatively, the "reliability" of the
informant's report in this particular case.

															The Illinois court, alluding to an elaborate set of legal rules
that have developed among various lower courts to enforce the
"two-pronged test," [ Footnote
4 ] found that the test had not been satisfied. First, the
"veracity" prong was not satisfied because

															"[t]here was simply no basis [for] conclud[ing] that the
anonymous person [who wrote the letter to the Bloomingdale Police
Department] was credible." Id. at 385, 423 N.E.2d at 891. The court indicated that
corroboration by police of details contained in the letter might
never satisfy the "veracity" prong, and in any event, could not do
so if, as in the present case, only "innocent" details are
corroborated. Id. at 390, 423 N.E.2d at 893. In addition,
the letter gave no indication of the basis of its writer's
knowledge of the Page 462 U. S. 230 Gateses' activities. The Illinois court understood Spinelli as permitting the detail contained in a tip to be
used to infer that the informant had a reliable basis for his
statements, but it thought that the anonymous letter failed to
provide sufficient detail to permit such an inference. Thus, it
concluded that no showing of probable cause had been made.

															We agree with the Illinois Supreme Court that an informant's
"veracity," "reliability," and "basis of knowledge" are all highly
relevant in determining the value of his report. We do not agree,
however, that these elements should be understood as entirely
separate and independent requirements to be rigidly exacted in
every case, [ Footnote 5 ] which
the opinion of the Supreme Court of Illinois would imply. Rather,
as detailed below, they should be understood simply as closely
intertwined issues that may usefully illuminate the common sense,
practical question whether there is "probable cause" to believe
that contraband or evidence is located in a particular place. III This totality-of-the-circumstances approach is far more
consistent with our prior treatment of probable cause [ Footnote 6 ] than Page 462 U. S. 231 is any rigid demand that specific "tests" be satisfied by every
informant's tip. Perhaps the central teaching of our decisions
bearing on the probable cause standard is that it is a "practical,
nontechnical conception." Brinegar v. United States, 338 U. S. 160 , 338 U. S. 176 (1949).

															"In dealing with probable cause, . . . as the very name implies,
we deal with probabilities. These are not technical; they are the
factual and practical considerations of everyday life on which
reasonable and prudent men, not legal technicians, act." Id. at 338 U. S. 175 .
Our observation in United States v. Cortez, 449 U.
S. 411 , 449 U. S. 418 (1981), regarding "particularized suspicion," is also applicable to
the probable cause standard:

															"The process does not deal with hard certainties, but with
probabilities. Long before the law of probabilities was articulated
as such, practical people formulated certain common sense
conclusions about human behavior; jurors as factfinders are
permitted to do the same -- and Page 462 U. S. 232 so are law enforcement officers. Finally, the evidence thus
collected must be seen and weighed not in terms of library analysis
by scholars, but as understood by those versed in the field of law
enforcement."

															As these comments illustrate, probable cause is a fluid concept
-- turning on the assessment of probabilities in particular factual
contexts -- not readily, or even usefully, reduced to a neat set of
legal rules. Informants' tips doubtless come in many shapes and
sizes from many different types of persons. As we said in Adams
v. Williams, 407 U. S. 143 , 407 U. S. 147 (1972):

															"Informants' tips, like all other clues and evidence coming to a
policeman on the scene, may vary greatly in their value and
reliability."

															Rigid legal rules are ill-suited to an area of such diversity.
"One simple rule will not cover every situation." Ibid. [ Footnote 7 ] Page 462 U. S. 233 Moreover, the "two-pronged test" directs analysis into two
largely independent channels -- the informant's "veracity" or
"reliability" and his "basis of knowledge." See nn. 4 and | 4 and S. 213fn5|>5, supra. There are
persuasive arguments against according these two elements such
independent status. Instead, they are better understood as relevant
considerations in the totality-of-the-circumstances analysis that
traditionally has guided probable cause determinations: a
deficiency in one may be compensated for, in determining the
overall reliability of a tip, by a strong showing as to the other,
or by some other indicia of reliability. See, e.g., Adams v.
Williams, supra, at 407 U. S.
146 -147; United States v. Harris, 403 U.
S. 573 (1971).

															If, for example, a particular informant is known for the unusual
reliability of his predictions of certain types of criminal
activities in a locality, his failure, in a particular case, to
thoroughly set forth the basis of his knowledge surely should not
serve as an absolute bar to a finding of probable cause based on
his tip. See United States v. Sellers, 483 F.2d 37 (CA5
1973). [ Footnote 8 ] Likewise,
if an unquestionably honest citizen comes forward with a report of
criminal activity -- which, if fabricated, would subject him to
criminal liability -- we have found Page 462 U. S. 234 rigorous scrutiny of the basis of his knowledge unnecessary. Adams v. Williams, supra. Conversely, even if we entertain
some doubt as to an informant's motives, his explicit and detailed
description of alleged wrongdoing, along with a statement that the
event was observed first-hand, entitles his tip to greater weight
than might otherwise be the case. Unlike a
totality-of-the-circumstances analysis, which permits a balanced
assessment of the relative weights of all the various indicia of
reliability (and unreliability) attending an informant's tip, the
"two-pronged test" has encouraged an excessively technical
dissection of informants' tips, [ Footnote 9 ] with undue attention's Page 462 U. S. 235 being focused on isolated issues that cannot sensibly be
divorced from the other facts presented to the magistrate.

															As early as Locke v. United
States , 7 Cranch 339, 11 U. S. 348 (1813), Chief Justice Marshall observed, in a closely related
context:

															"[T]he term 'probable cause,' according to its usual
acceptation, means less than evidence which would justify
condemnation. . . . It imports a seizure made under circumstances
which warrant suspicion."

															More recently, we said that "the quanta . . . of proof"
appropriate in ordinary judicial proceedings are inapplicable to
the decision to issue a warrant. Brinegar, 338 U.S. at 338 U. S. 173 .
Finely tuned standards such as proof beyond a reasonable doubt or
by a preponderance of the evidence, useful in formal trials, have
no place in the magistrate's decision. While an effort to fix some
general, numerically precise degree of certainty corresponding to
"probable cause" may not be helpful, it is clear that "only the
probability, and not a prima facie showing, of criminal
activity, is the standard of probable cause." Spinelli, 393 U.S. at 393 U. S. 419 . See Model Code of Pre-Arraignment Procedure § 210.1(7)
(Prop.Off.Draft 1972); 1 W. LaFave, Search and Seizure § 3.2(e)
(1978).

															We also have recognized that affidavits

															"are normally drafted by nonlawyers in the midst and haste of a
criminal investigation. Technical requirements of elaborate
specificity once exacted under common law pleadings have no proper
place in this area." United States v. Ventresca, 380 U.
S. 102 , 380 U. S. 108 (1965). Likewise, search and arrest warrants long have been issued
by persons who are neither lawyers nor judges, and who certainly do
not remain abreast of each judicial refinement of the nature of
"probable cause." See Shadwick v. City of Tampa, 407 U. S. 345 , 407 U. S.
348 -350 (1972). The rigorous inquiry into the Spinelli prongs and the complex superstructure of
evidentiary and analytical rules that some have seen implicit in
our Spinelli decision, cannot be reconciled with the fact
that many warrants are -- quite properly, 407 U.S. at 407 U. S.
348 -350 -- issued on the basis of nontechnical, Page 462 U. S. 236 common sense judgments of laymen applying a standard less
demanding than those used in more formal legal proceedings.
Likewise, given the informal, often hurried context in which it
must be applied, the "built-in subtleties," Stanley v.
State, 19 Md.App. 507, 528, 313
A.2d 847 , 860 (1974), of the "two-pronged test" are
particularly unlikely to assist magistrates in determining probable
cause.

															Similarly, we have repeatedly said that after-the-fact scrutiny
by courts of the sufficiency of an affidavit should not take the
form of de novo review. A magistrate's "determination of
probable cause should be paid great deference by reviewing courts." Spinelli, supra, at 393 U. S. 419 .
"A grudging or negative attitude by reviewing courts toward
warrants," Ventresca, 380 U.S. at 380 U. S. 108 ,
is inconsistent with the Fourth Amendment's strong preference for
searches conducted pursuant to a warrant; "courts should not
invalidate warrant[s] by interpreting affidavit[s] in a
hypertechnical, rather than a common sense, manner." Id. at 380 U. S.
109 .

															If the affidavits submitted by police officers are subjected to
the type of scrutiny some courts have deemed appropriate, police
might well resort to warrantless searches, with the hope of relying
on consent or some other exception to the Warrant Clause that might
develop at the time of the search. In addition, the possession of a
warrant by officers conducting an arrest or search greatly reduces
the perception of unlawful or intrusive police conduct, by
assuring

															"the individual whose property is searched or seized of the
lawful authority of the executing officer, his need to search, and
the limits of his power to search." United States v. Chadwick, 433 U. S.
1 , 433 U. S. 9 (1977). Reflecting this preference for the warrant process, the
traditional standard for review of an issuing magistrate's probable
cause determination has been that, so long as the magistrate had a
"substantial basis for . . . conclud[ing]" that a search would
uncover evidence of wrongdoing, the Fourth Amendment requires no
more. Jones v. United States, 362 U.
S. 257 , 362 U. S. 271 (1960). See United States v. Page 462 U. S. 237 Harris, 403 U.S. at 403 U. S.
577 -583. [ Footnote
10 ] We think reaffirmation of this standard better serves the
purpose of encouraging recourse to the warrant procedure and is
more consistent with our traditional deference to the probable
cause determinations of magistrates than is the "two-pronged
test."

															Finally, the direction taken by decisions following Spinelli poorly serves "[t]he most basic function of any
government:" "to provide for the security of the individual and of
his property." Miranda v. Arizona, 384 U.
S. 436 , 384 U. S. 539 (1966) (WHITE, J., dissenting). The strictures that inevitably
accompany the "two-pronged test" cannot avoid seriously impeding
the task of law enforcement, see, e.g., n 9, supra. If, as the Illinois
Supreme Court apparently thought, that test must be rigorously
applied in every case, anonymous tips would be of greatly
diminished value in police work. Ordinary citizens, like ordinary
witnesses, see Advisory Committee's Notes on Fed.Rule
Evid. 701, 28 U.S.C.App. p. 570, generally do not provide extensive
recitations of the basis of their everyday observations. Likewise,
as the Illinois Supreme Court observed in this case, the veracity
of persons supplying anonymous tips is, by hypothesis, largely
unknown, and unknowable. As a result, anonymous tips seldom could
survive a rigorous application of either of the Spinelli prongs. Yet such tips, particularly when supplemented by Page 462 U. S. 238 independent police investigation, frequently contribute to the
solution of otherwise "perfect crimes." While a conscientious
assessment of the basis for crediting such tips is required by the
Fourth Amendment, a standard that leaves virtually no place for
anonymous citizen informants is not. For all these reasons, we
conclude that it is wiser to abandon the "two-pronged test"
established by our decisions in Aguilar and Spinelli. [ Footnote
11 ] In its place, we reaffirm the totality-of-the-circumstances
analysis that traditionally has informed probable cause
determinations. See Jones v. United States, supra; United
States v. Ventresca, 380 U. S. 102 (1965); Brinegar v. United States, 338 U.
S. 160 (1949). The task of the issuing magistrate is
simply to make a practical, common sense decision whether, given
all the circumstances set forth in the affidavit before him,
including the "veracity" and "basis of knowledge" of persons
supplying hearsay information, there is a fair probability that
contraband or evidence of a crime will be found in a particular
place. And the duty of a reviewing court is simply to ensure that
the magistrate had a "substantial basis for . . . conclud[ing]"
that probable cause Page 462 U. S. 239 existed. Jones v. United States, 362 U.S. at 362 U. S. 271 .
We are convinced that this flexible, easily applied standard will
better achieve the accommodation of public and private interests
that the Fourth Amendment requires than does the approach that has
developed from Aguilar and Spinelli. Our earlier cases illustrate the limits beyond which a
magistrate may not venture in issuing a warrant. A sworn statement
of an affiant that "he has cause to suspect and does believe" that
liquor illegally brought into the United States is located on
certain premises will not do. Nathanson v. United States, 290 U. S. 41 (1933). An affidavit must provide the magistrate with a substantial
basis for determining the existence of probable cause, and the
wholly conclusory statement at issue in Nathanson failed
to meet this requirement. An officer's statement that "[a]ffiants
have received reliable information from a credible person and do
believe" that heroin is stored in a home, is likewise inadequate. Aguilar v. Texas, 378 U. S. 108 (1964). As in Nathanson, this is a mere conclusory
statement that gives the magistrate virtually no basis at all for
making a judgment regarding probable cause. Sufficient information
must be presented to the magistrate to allow that official to
determine probable cause; his action cannot be a mere ratification
of the bare conclusions of others. In order to ensure that such an
abdication of the magistrate's duty does not occur, courts must
continue to conscientiously review the sufficiency of affidavits on
which warrants are issued. But when we move beyond the "bare bones"
affidavits present in cases such as Nathanson and Aguilar, this area simply does not lend itself to a
prescribed set of rules, like that which had developed from Spinelli. Instead, the flexible, common sense standard
articulated in Jones, Ventresca, and Brinegar better serves the purposes of the Fourth Amendment's probable cause
requirement.

															JUSTICE BRENNAN's dissent suggests in several places that the
approach we take today somehow downgrades the Page 462 U. S. 240 role of the neutral magistrate, because Aguilar and Spinelli "preserve the role of magistrates as independent
arbiters of probable cause. . . ." Post at 462 U. S. 287 .
Quite the contrary, we believe, is the case. The essential
protection of the warrant requirement of the Fourth Amendment, as
stated in Johnson v. United States, 333 U. S.
10 (1948), is in

															"requiring that [the usual inferences which reasonable men draw
from evidence] be drawn by a neutral and detached magistrate,
instead of being judged by the officer engaged in the often
competitive enterprise of ferreting out crime." Id. at 333 U. S. 13 -14.
Nothing in our opinion in any way lessens the authority of the
magistrate to draw such reasonable inferences as he will from the
material supplied to him by applicants for a warrant; indeed, he is
freer than under the regime of Aguilar and Spinelli to draw such inferences, or to refuse to draw
them if he is so minded.

															The real gist of JUSTICE BRENNAN's criticism seems to be a
second argument, somewhat at odds with the first, that magistrates
should be restricted in their authority to make probable cause
determinations by the standards laid down in Aguilar and Spinelli, and that such findings

															"should not be authorized unless there is some assurance that
the information on which they are based has been obtained in a
reliable way by an honest or credible person." Post at 462 U. S. 283 .
However, under our opinion, magistrates remain perfectly free to
exact such assurances as they deem necessary, as well as those
required by this opinion, in making probable cause determinations.
JUSTICE BRENNAN would apparently prefer that magistrates be
restricted in their findings of probable cause by the development
of an elaborate body of case law dealing with the "veracity" prong
of the Spinelli test, which in turn is broken down into
two "spurs" -- the informant's "credibility" and the "reliability"
of his information, together with the "basis of knowledge" prong of
the Spinelli test. See n 4, supra. That such a labyrinthine body of
judicial refinement bears any relationship to familiar definitions
of Page 462 U. S. 241 probable cause is hard to imagine. As previously noted, probable
cause deals

															"with probabilities. These are not technical; they are the
factual and practical considerations of everyday life on which
reasonable and prudent men, not legal technicians, act," Brinegar v. United States, 338 U.S. at 338 U. S.
175 .

															JUSTICE BRENNAN's dissent also suggests that

															"[w]ords such as 'practical,' 'nontechnical,' and 'common
sense,' as used in the Court's opinion, are but code words for an
overly permissive attitude towards police practices in derogation
of the rights secured by the Fourth Amendment." Post at 462 U. S. 290 .
An easy, but not a complete, answer to this rather florid statement
would be that nothing we know about Justice Rutledge suggests that
he would have used the words he chose in Brinegar in such
a manner. More fundamentally, no one doubts that,

															"under our Constitution, only measures consistent with the
Fourth Amendment may be employed by government to cure [the horrors
of drug trafficking]," post at 462 U. S. 290 ;
but this agreement does not advance the inquiry as to which
measures are, and which measures are not, consistent with the
Fourth Amendment. "Fidelity" to the commands of the Constitution
suggests balanced judgment, rather than exhortation. The highest
"fidelity" is not achieved by the judge who instinctively goes
furthest in upholding even the most bizarre claim of individual
constitutional rights, any more than it is achieved by a judge who
instinctively goes furthest in accepting the most restrictive
claims of governmental authorities. The task of this Court, as of
other courts, is to "hold the balance true," and we think we have
done that in this case. IV Our decisions applying the totality-of-the-circumstances
analysis outlined above have consistently recognized the value of
corroboration of details of an informant's tip by independent
police work. In Jones v. United States, 362 U.S. at 362 U. S. 269 ,
we held that an affidavit relying on hearsay "is not to Page 462 U. S. 242 be deemed insufficient on that score so long as a substantial
basis for crediting the hearsay is presented." We went on to say
that, even in making a warrantless arrest, an officer

															"may rely upon information received through an informant, rather
than upon his direct observations, so long as the informant's
statement is reasonably corroborated by other matters within the
officer's knowledge." Ibid. Likewise, we recognized the probative value of
corroborative efforts of police officials in Aguilar --
the source of the "two-pronged test" -- by observing that, if the
police had made some effort to corroborate the informant's report
at issue, "an entirely different case" would have been presented. Aguilar, 378 U.S. at 378 U. S. 109 ,
n. 1.

															Our decision in Draper v. United States, 358 U.
S. 307 (1959), however, is the classic case on the value
of corroborative efforts of police officials. There, an informant
named Hereford reported that Draper would arrive in Denver on a
train from Chicago on one of two days, and that he would be
carrying a quantity of heroin. The informant also supplied a fairly
detailed physical description of Draper, and predicted that he
would be wearing a light colored raincoat, brown slacks, and black
shoes, and would be walking "real fast." Id. at 358 U. S. 309 .
Hereford gave no indication of the basis for his information.
[ Footnote 12 ]

															On one of the stated dates, police officers observed a man
matching this description exit a train arriving from Chicago; his
attire and luggage matched Hereford's report, and he was Page 462 U. S. 243 walking rapidly. We explained in Draper that, by this
point in his investigation, the arresting officer

															"had personally verified every facet of the information given
him by Hereford except whether petitioner had accomplished his
mission, and had the three ounces of heroin on his person or in his
bag. And surely, with every other bit of Hereford's information
being thus personally verified, [the officer] had 'reasonable
grounds' to believe that the remaining unverified bit of Hereford's
information -- that Draper would have the heroin with him -- was
likewise true," id. at 358 U. S.
313 .

															The showing of probable cause in the present case was fully as
compelling as that in Draper. Even standing alone, the
facts obtained through the independent investigation of Mader and
the DEA at least suggested that the Gateses were involved in drug
trafficking. In addition to being a popular vacation site, Florida
is well known as a source of narcotics and other illegal drugs. See United States v. Mendenhall, 446 U.
S. 544 , 446 U. S. 562 (1980) (POWELL, J., concurring in part and concurring in judgment);
DEA, Narcotics Intelligence Estimate, The Supply of Drugs to the
U.S. Illicit Market From Foreign and Domestic Sources in 1980, pp.
8-9. Lance Gates' flight to West Palm Beach, his brief, overnight
stay in a motel, and apparent immediate return north to Chicago in
the family car, conveniently awaiting him in West Palm Beach, is as
suggestive of a prearranged drug run, as it is of an ordinary
vacation trip.

															In addition, the judge could rely on the anonymous letter, which
had been corroborated in major part by Mader's efforts -- just as
had occurred in Draper. [ Footnote 13 ] The Supreme Court Page 462 U. S. 244 of Illinois reasoned that Draper involved an informant
who had given reliable information on previous occasions, while the
honesty and reliability of the anonymous informant in this case
were unknown to the Bloomingdale police. While this distinction
might be an apt one at the time the Police Department received the
anonymous letter, it became far less significant after Mader's
independent investigative work occurred. The corroboration of the
letter's predictions that the Gateses' car would be in Florida,
that Lance Gates would fly to Florida in the next day or so, and
that he would drive the car north toward Bloomingdale all
indicated, albeit not with certainty, that the informant's other
assertions also were true. "[B]ecause an informant is right about
some things, he is more probably right about other facts," Spinelli, 393 U.S. at 393 U. S. 427 (WHITE, J., concurring) -- including the claim regarding the
Gateses' illegal activity. This may well not be the type of
"reliability" or "veracity" necessary to satisfy some views of the
"veracity prong" of Spinelli, but we think it suffices for
the practical, common sense judgment called for in making a
probable cause determination. It is enough, for purposes of
assessing probable cause, that "[c]orroboration through other
sources of information reduced the Page 462 U. S. 245 chances of a reckless or prevaricating tale," thus providing "a
substantial basis for crediting the hearsay." Jones v. United
States, 362 U.S. at 362 U. S. 269 , 362 U. S.
271 .

															Finally, the anonymous letter contained a range of details
relating not just to easily obtained facts and conditions existing
at the time of the tip, but to future actions of third parties
ordinarily not easily predicted. The letterwriter's accurate
information as to the travel plans of each of the Gateses was of a
character likely obtained only from the Gateses themselves, or from
someone familiar with their not entirely ordinary travel plans. If
the informant had access to accurate information of this type a
magistrate could properly conclude that it was not unlikely that he
also had access to reliable information of the Gateses' alleged
illegal activities. [ Footnote
14 ] Of Page 462 U. S. 246 course, the Gateses' travel plans might have been learned from a
talkative neighbor or travel agent; under the "two-pronged test"
developed from Spinelli, the character of the details in
the anonymous letter might well not permit a sufficiently clear
inference regarding the letterwriter's "basis of knowledge." But,
as discussed previously, supra, at 462 U. S. 235 ,
probable cause does not demand the certainty we associate with
formal trials. It is enough that there was a fair probability that
the writer of the anonymous letter had obtained his entire story
either from the Gateses or someone they trusted. And corroboration
of major portions of the letter's predictions provides just this
probability. It is apparent, therefore, that the judge issuing the
warrant had a "substantial basis for . . . conclud[ing]" that
probable cause to search the Gateses' home and car existed. The
judgment of the Supreme Court of Illinois therefore must be Reversed. [ Footnote 1 ]

															The apparent rule of Crowell v. Randell that a federal
claim have been both raised and addressed in state court was
generally not understood in the literal fashion in which it was
phrased. See R. Robertson & F. Kirkham, Jurisdiction
of the Supreme Court of the United States § 60 (1951). Instead, the
Court developed the rule that a claim would not be considered here
unless it had been either raised or squarely considered and
resolved in state court. See, e.g., McGoldrick v. Compagnie
Generale Transatlantique, 309 U. S. 430 , 309 U. S.
434 -435 (1940); State Farm Mutual Ins. Co. v.
Duel, 324 U. S. 154 , 324 U. S. 160 (1945).

															[ Footnote 2 ]

															In Dewey, certain assessments had been levied against
the owner of property abutting a street paved by the city; a state
trial court ordered that the property be forfeited when the
assessments were not paid, and in addition, held the plaintiff in
error personally liable for the amount by which the assessments
exceeded the value of the lots. In state court, the plaintiff in
error argued that the imposition of personal liability against him
violated the Due Process Clause of the Fourteenth Amendment,
because he had not received personal notice of the assessment
proceedings. In this Court, he also attempted to argue that the
assessment itself constituted a taking under the Fourteenth
Amendment. The Court held that, beyond arising from a single
factual occurrence, the two claims "are not in anywise necessarily
connected," 173 U.S. at 173 U. S. 198 .
Because of this, we concluded that the plaintiff in error's taking
claim could not be considered.

															[ Footnote 3 ]

															In Spinelli, police officers observed Mr. Spinelli
going to and from a particular apartment, which the telephone
company said contained two telephones with stated numbers. The
officers also were "informed by a confidential reliable informant
that William Spinelli [was engaging in illegal gambling
activities]" at the apartment, and that he used two phones, with
numbers corresponding to those possessed by the police. 393 U.S. at 393 U. S. 414 .
The officers submitted an affidavit with this information to a
magistrate and obtained a warrant to search Spinelli's apartment.
We held that the magistrate could have made his determination of
probable cause only by "abdicating his constitutional function," id. at 393 U. S. 416 .
The Government's affidavit contained absolutely no information
regarding the informant's reliability. Thus, it did not satisfy Aguilar's requirement that such affidavits contain "some
of the underlying circumstances" indicating that "the informant . .
. was credible'" or that "his information [was] `reliable.'" Aguilar v. Texas, 378 U. S. 108 , 378 U. S. 114 (1964). In addition, the tip failed to satisfy Aguilar's requirement that it detail "some of the underlying circumstances
from which the informant concluded that . . . narcotics were where
he claimed they were." Ibid. We also held that, if the tip
concerning Spinelli had contained "sufficient detail" to permit the
magistrate to conclude "that he [was] relying on something more substantial than a
casual rumor circulating in the underworld or an accusation based
merely on an individual's general reputation,"

															393 U.S. at 393 U. S. 416 ,
then he properly could have relied on it; we thought, however, that
the tip lacked the requisite detail to permit this "self-verifying
detail" analysis.

															[ Footnote 4 ] See, e.g., Stanley v. State, 19 Md.App. 507, 313 A.2d 847 (1974). In summary, these rules posit that the
"veracity" prong of the Spinelli test has two "spurs" --
the informant's "credibility" and the "reliability" of his
information. Various interpretations are advanced for the meaning
of the "reliability" spur of the "veracity" prong. Both the "basis
of knowledge" prong and the "veracity" prong are treated as
entirely separate requirements, which must be independently
satisfied in every case in order to sustain a determination of
probable cause. See n 5, infra. Some ancillary doctrines are relied on to
satisfy certain of the foregoing requirements. For example, the
"self-verifying detail" of a tip may satisfy the "basis of
knowledge" requirement, although not the "credibility" spur of the
"veracity" prong. See 85 Ill. 2d at 388, 423 N.E.2d at
892. Conversely, corroboration would seem not capable of supporting
the "basis of knowledge" prong, but only the "veracity" prong. Id. at 390, 423 N.E.2d at 893.

															The decision in Stanley, while expressly approving and
conscientiously attempting to apply the "two-pronged test,"
observes that "[t]he built-in subtleties [of the test] are such,
however, that a slipshod application calls down upon us the fury of
Murphy's Law." 19 Md.App. at 528, 313 A.2d at 860 (footnote
omitted). The decision also suggested that it is necessary to
"evolve analogous guidelines [to hearsay rules employed in trial
settings] for the reception of hearsay in a probable cause
setting." Id. at 522, n. 12, 313 A.2d at 857, n. 12.

															[ Footnote 5 ]

															The entirely independent character that the Spinelli prongs have assumed is indicated both by the opinion of the
Illinois Supreme Court in this case, and by decisions of other
courts. One frequently cited decision Stanley v. State,
supra, at 530, 313 A.2d at 861 (footnote omitted), remarks
that

															"the dual requirements represented by the 'two-pronged test' are
'analytically severable,' and an 'overkill' on one prong will not
carry over to make up for a deficit on the other prong." See also n 9, infra. [ Footnote 6 ]

															Our original phrasing of the so-called "two-pronged test" in Aguilar v. Texas, supra, suggests that the two prongs were
intended simply as guides to a magistrate's determination of
probable cause, not as inflexible, independent requirements
applicable in every case. In Aguilar, we required only
that

															"the magistrate must be informed of some of the underlying
circumstances from which the informant concluded that . . .
narcotics were where he claimed they were, and some of the
underlying circumstances from which the officer concluded that
the informant . . . was 'credible' or his information
'reliable.'" Id. at 378 U. S. 114 (emphasis added). As our language indicates, we intended neither a
rigid compartmentalization of the inquiries into an informant's
"veracity," "reliability," and "basis of knowledge," nor that these
inquiries be elaborate exegeses of an informant's tip. Rather, we
required only that some facts bearing on two particular
issues be provided to the magistrate. Our decision in Jaben v.
United States, 381 U. S. 214 (1965), demonstrated this latter point. We held there that a
criminal complaint showed probable cause to believe the defendant
had attempted to evade the payment of income taxes. We
commented:

															"Obviously, any reliance upon factual allegations necessarily
entails some degree of reliability upon the credibility of the
source. . . . Nor does it indicate that each factual allegation
which the affiant puts forth must be independently documented, or
that each and every fact which contributed to his conclusions be
spelled out in the complaint. . . . It simply requires that
enough information be presented to the Commissioner to enable him
to make the judgment that the charges are not capricious and are
sufficiently supported to justify bringing into play the further
steps of the criminal process. " Id. at 378 U. S.
224 -225 (emphasis added).

															[ Footnote 7 ]

															The diversity of informants' tips, as well as the usefulness of
the totality-of-the-circumstances approach to probable cause, is
reflected in our prior decisions on the subject. In Jones v.
United States, 362 U. S. 257 , 362 U. S. 271 (1960), we held that probable cause to search petitioners'
apartment was established by an affidavit based principally on an
informant's tip. The unnamed informant claimed to have purchased
narcotics from petitioners at their apartment; the affiant stated
that he had been given correct information from the informant on a
prior occasion. This, and the fact that petitioners had admitted to
police officers on another occasion that they were narcotics users,
sufficed to support the magistrate's determination of probable
cause.

															Likewise, in Rugendorf v. United States, 376 U.
S. 528 (1964), the Court upheld a magistrate's
determination that there was probable cause to believe that certain
stolen property would be found in petitioner's apartment. The
affidavit submitted to the magistrate stated that certain furs had
been stolen, and that a confidential informant, who previously had
furnished confidential information, said that he saw the furs in
petitioner's home. Moreover, another confidential informant, also
claimed to be reliable, stated that one Schweihs had stolen the
furs. Police reports indicated that petitioner had been seen in
Schweihs' company, and a third informant stated that petitioner was
a fence for Schweihs.

															Finally, in Ker v. California, 374 U. S.
23 (1963), we held that information within the knowledge
of officers who searched the Kers' apartment provided them with
probable cause to believe drugs would be found there. The officers
were aware that one Murphy had previously sold marihuana to a
police officer; the transaction had occurred in an isolated area,
to which Murphy had led the police. The night after this
transaction, police observed Mr. Ker and Murphy meet in the same
location. Murphy approached Ker's car, and, although police could
see nothing change hands, Murphy's modus operandi was identical to
what it had been the night before. Moreover, when police followed
Ker from the scene of the meeting with Murphy, he managed to lose
them after performing an abrupt U-turn. Finally, the police had a
statement from an informant who had provided reliable information
previously, that Ker was engaged in selling marihuana, and that his
source was Murphy. We concluded that

															"[t]o say that this coincidence of information was sufficient to
support a reasonable belief of the officers that Ker was illegally
in possession of marijuana is to indulge in understatement." Id. at 374 U. S.
36 .

															[ Footnote 8 ] Compare Stanley v. State, 19 Md.App. at 530, 313 A.2d
at 861, reasoning that,

															"[e]ven assuming 'credibility' amounting to sainthood, the judge
still may not accept the bare conclusion . . . of a sworn and known
and trusted police affiant."

															[ Footnote 9 ]

															Some lower court decisions, brought to our attention by the
State, reflect a rigid application of such rules. In Bridger v.
State, 503
S.W.2d 801 (Tex.Crim.App.1974), the affiant had received a
confession of armed robbery from one of two suspects in the
robbery; in addition, the suspect had given the officer $800 in
cash stolen during the robbery. The suspect also told the officer
that the gun used in the robbery was hidden in the other suspect's
apartment. A warrant issued on the basis of this was invalidated on
the ground that the affidavit did not satisfactorily describe how
the accomplice had obtained his information regarding the gun.

															Likewise, in People v. Palanza, 55 Ill.App.3d 1028, 371
N.E.2d 687 (1978), the affidavit submitted in support of an
application for a search warrant stated that an informant of proven
and uncontested reliability had seen, in specifically described
premises,

															"a quantity of a white crystalline substance which was
represented to the informant by a white male occupant of the
premises to be cocaine. Informant has observed cocaine on numerous
occasions in the past and is thoroughly familiar with its
appearance. The informant states that the white crystalline powder
he observed in the above described premises appeared to him to be
cocaine." Id. at 1029, 371 N.E.2d at 688. The warrant issued on
the basis of the affidavit was invalidated because

															"[t]here is no indication as to how the informant or for that
matter any other person could tell whether a white substance was
cocaine and not some other substance such as sugar or salt." Id. at 1030, 371 N.E.2d at 689.

															Finally, in People v. Brethauer, 174 Colo. 29, 482 P.2d 369 (1971), an informant, stated to have supplied reliable information
in the past, claimed that L.S.D. and marihuana were located on
certain premises. The informant supplied police with drugs, which
were tested by police and confirmed to be illegal substances. The
affidavit setting forth these, and other, facts was found defective
under both prongs of Spinelli. [ Footnote 10 ]

															We also have said that,

															"[a]lthough in a particular case it may not be easy to determine
when an affidavit demonstrates the existence of probable cause, the
resolution of doubtful or marginal cases in this area should be
largely determined by the preference to be accorded to
warrants," United States v. Ventresca, 380 U.
S. 102 , 380 U. S. 109 (1965). This reflects both a desire to encourage use of the warrant
process by police officers and a recognition that, once a warrant
has been obtained, intrusion upon interests protected by the Fourth
Amendment is less severe than otherwise may be the case. Even if we
were to accept the premise that the accurate assessment of probable
cause would be furthered by the "two-pronged test," which we do
not, these Fourth Amendment policies would require a less rigorous
standard than that which appears to have been read into Aguilar and Spinelli. [ Footnote 11 ]

															The Court's decision in Spinelli has been the subject
of considerable criticism, both by Members of this Court and
others. JUSTICE BLACKMUN, concurring in United States v.
Harris, 403 U. S. 573 , 403 U. S.
585 -586 (1971), noted his long-held view "that Spinelli . . . was wrongly decided" by this Court. Justice
Black similarly would have overruled that decision. Id. at 403 U. S. 585 .
Likewise, a noted commentator has observed that "[t]he Aguilar-Spinelli formulation has provoked apparently
ceaseless litigation." 8A J. Moore, Moore's Federal Practice �
41.04, p. 41-43 (1982).

															Whether the allegations submitted to the magistrate in Spinelli would, under the view we now take, have supported
a finding of probable cause, we think it would not be profitable to
decide. There are so many variables in the probable cause equation
that one determination will seldom be a useful "precedent" for
another. Suffice it to say that, while we in no way abandon Spinelli's concern for the trustworthiness of informers
and for the principle that it is the magistrate who must ultimately
make a finding of probable cause, we reject the rigid
categorization suggested by some of its language.

															[ Footnote 12 ]

															The tip in Draper might well not have survived the rigid
application of the "two-pronged test" that developed following Spinelli. The only reference to Hereford's reliability was
that he had

															"been engaged as a 'special employee' of the Bureau of Narcotics
at Denver for about six months, and from time to time gave
information to [the police for] small sums of money, and that [the
officer] had always found the information given by Hereford to be
accurate and reliable."

															358 U.S. at 358 U. S. 309 .
Likewise, the tip gave no indication of how Hereford came by his
information. At most, the detailed and accurate predictions in the
tip indicated that, however Hereford obtained his information, it
was reliable.

															[ Footnote 13 ]

															The Illinois Supreme Court thought that the verification of
details contained in the anonymous letter in this case amounted
only to "[t]he corroboration of innocent activity," 85 Ill. 2d
376 , 390, 423 N.E.2d
887 , 893 (1981), and that this was insufficient to support a
finding of probable cause. We are inclined to agree, however, with
the observation of Justice Moran in his dissenting opinion that
"[i]n this case, just as in Draper, seemingly innocent
activity became suspicious in light of the initial tip." Id. at 396, 423 N.E.2d at 896. And it bears noting that
all of the corroborating detail established in Draper was
of entirely innocent activity -- a fact later pointed out by the
Court in both Jones v. United States, 362 U.S. at 362 U. S.
269 -270, and Ker v. California, 374 U.S. at 374 U. S.
36 .

															This is perfectly reasonable. As discussed previously, probable
cause requires only a probability or substantial chance of criminal
activity, not an actual showing of such activity. By hypothesis,
therefore, innocent behavior frequently will provide the basis for
a showing of probable cause; to require otherwise would be to sub silentio impose a drastically more rigorous definition
of probable cause than the security of our citizens' demands. We
think the Illinois court attempted a too rigid classification of
the types of conduct that may be relied upon in seeking to
demonstrate probable cause. See Brown v. Texas, 443 U. S. 47 , 443 U. S. 52 , n.
2 (1979). In making a determination of probable cause, the relevant
inquiry is not whether particular conduct is "innocent" or
"guilty," but the degree of suspicion that attaches to particular
types of noncriminal acts.

															[ Footnote 14 ]

															JUSTICE STEVENS' dissent seizes on one inaccuracy in the
anonymous informant's letter -- its statement that Sue Gates would
fly from Florida to Illinois, when in fact she drove -- and argues
that the probative value of the entire tip was undermined by this
allegedly "material mistake." We have never required that
informants used by the police be infallible, and can see no reason
to impose such a requirement in this case. Probable cause,
particularly when police have obtained a warrant, simply does not
require the perfection the dissent finds necessary.

															Likewise, there is no force to the dissent's argument that the
Gateses' action in leaving their home unguarded undercut the
informant's claim that drugs were hidden there. Indeed, the
line-by-line scrutiny that the dissent applies to the anonymous
letter is akin to that which we find inappropriate in reviewing
magistrates' decisions. The dissent apparently attributes to the
judge who issued the warrant in this case the rather implausible
notion that persons dealing in drugs always stay at home,
apparently out of fear that to leave might risk intrusion by
criminals. If accurate, one could not help sympathizing with the
self-imposed isolation of people so situated. In reality, however,
it is scarcely likely that the judge ever thought that the
anonymous tip "kept one spouse" at home, much less that he relied
on the theory advanced by the dissent. The letter simply says that
Sue would fly from Florida to Illinois, without indicating whether
the Gateses made the bitter choice of leaving the drugs in their
house, or those in their car, unguarded. The judge's determination
that there might be drugs or evidence of criminal activity in the
Gateses' home was well supported by the less speculative theory,
noted in text, that, if the informant could predict with
considerable accuracy the somewhat unusual travel plans of the
Gateses, he probably also had a reliable basis for his statements
that the Gateses kept a large quantity of drugs in their home and
frequently were visited by other drug traffickers there.

															JUSTICE WHITE, concurring in the judgment.

															In my view, the question regarding modification of the
exclusionary rule framed in our order of November 29, 1982, 459 U. S. 1028 (1982), is properly before us, and should be addressed. I continue
to believe that the exclusionary rule is an inappropriate remedy
where law enforcement officials act in the reasonable belief that a
search and seizure was consistent with the Fourth Amendment -- a
position I set forth in Stone v. Powell, 428 U.
S. 465 , 428 U. S.
537 -539 (1976). In this case, it was fully reasonable
for the Bloomingdale, Ill., police to believe that their search of
respondents' house and automobile comported with the Fourth
Amendment, as the search was conducted pursuant to a judicially
issued warrant. The Page 462 U. S. 247 exclusion of probative evidence where the constable has not
blundered not only sets the criminal free, but also fails to serve
any constitutional interest in securing compliance with the
important requirements of the Fourth Amendment. On this basis, I
concur in the Court's judgment that the decision of the Illinois
Supreme Court must be reversed. I The Court declines to address the exclusionary rule question
because the Illinois courts were not invited to modify the rule in
the first instance. The Court's refusal to face this important
question cannot be ascribed to jurisdictional limitations. I fully
agree that the statute which gives us jurisdiction in this cause,
28 U.S.C. § 1257(3), prevents us from deciding federal
constitutional claims raised here for the first time on review of
state court decisions. Cardinale v. Louisiana, 394 U. S. 437 , 394 U. S.
438 -439 (1969). But it is equally well established
that

															"'[n]o particular form of words or phrases is essential, but
only that the claim of invalidity and the ground therefor be
brought to the attention of the state court with fair precision and
in due time.'" Street v. New York, 394 U. S. 576 , 394 U. S. 584 (1969) (quoting New York ex rel. Bryant v. Zimmerman, 278 U. S. 63 , 278 U. S. 67 (1928)). Notwithstanding the select and controversial instances in
which the Court has reversed a state court decision for "plain
error," [ Footnote 2/1 ] we have
consistently dismissed for want of jurisdiction where the federal
claim asserted in this Court was not raised below. But this
obviously is not such a case. As the Court points out,

															"[i]t is clear in this case that respondents expressly raised,
at every level of the Illinois judicial system, the claim that the
Fourth Amendment had been violated by the actions of the
Illinois Page 462 U. S. 248 police, and that the evidence seized by the officers should be
excluded from their trial." Ante at 462 U. S. 220 .
Until today, we have not required more.

															We have never suggested that the jurisdictional stipulations of
§ 1257 require that all arguments on behalf of, let alone in
opposition to, a federal claim be raised and decided below.
[ Footnote 2/2 ] See R.
Stern & E. Gressman, Supreme Court Practice 230 (6th ed.1978). Dewey v. Des Moines, 173 U. S. 193 (1899), distinguished the raising of constitutional claims and the
making of arguments in support of or in opposition to those
claims.

															"If the question were only an enlargement of the one mentioned
in the assignment of errors, or if it were so connected with it in
substance as to form but another ground or reason for alleging the
invalidity of the personal judgment, we should have no hesitation
in holding the assignment sufficient to permit the question to be
now raised and argued."

															" Parties are not conned here to the same arguments which
were advanced in the courts below upon a Federal question there
discussed. " Id. at 173 U. S.
197 -198 (emphasis added). [ Footnote 2/3 ] Page 462 U. S. 249 Under Dewey, which the Court hails as the "fullest
treatment of the subject," ante at 462 U. S. 219 ,
the exclusionary rule issue is but another argument pertaining to
the Fourth Amendment question squarely presented in the Illinois
courts.

															The presentation and decision of respondents' Fourth Amendment
claim fully embraces the argument that due to the nature of the
alleged Fourth Amendment violation, the seized evidence should not
be excluded. Our decisions concerning the scope of the exclusionary
rule cannot be divorced from the Fourth Amendment; they rest on the
relationship of Fourth Amendment interests to the objectives of the
criminal justice system. See, e.g., United States v.
Ceccolini, 435 U. S. 268 (1978); Stone v. Powell, 428 U. S. 465 (1976). [ Footnote 2/4 ] Similarly,
the issues surrounding a proposed good faith modification are
intricately and inseverably tied to the nature of the Fourth
Amendment violation: the degree of probable cause, the presence of
a warrant, and the clarity of previously announced Fourth Amendment
principles all inform the Page 462 U. S. 250 good faith issue. The Court's own holding that the duty of a
reviewing court is simply to ensure that the magistrate had a
"substantial basis" for concluding that probable cause existed, ante at 462 U. S.
244 -245, is itself but a variation on the good faith
theme. See Brief for Petitioner on Reargument 4-26. As a
jurisdictional requirement, I have no doubt that the exclusionary
rule question is before us as an indivisible element of the claim
that the Constitution requires exclusion of certain evidence seized
in violation of the Fourth Amendment. As a prudential matter, I am
unmoved by the Court's lengthy discourse as to why it must avoid
the question. First, the Court turns on its head the axiom that

															"'due regard for the appropriate relationship of this Court to
state courts,' McGoldrick v. Compagnie Generale
Transatlantique, 309 U.S. at 309 U. S.
434 -435, demands that those courts be given an
opportunity to consider the constitutionality of the actions of
state officials," ante at 462 U. S. 221 .
This statement, written to explain why a state statute should not
be struck down on federal grounds not raised in the state courts,
[ Footnote 2/5 ] hardly applies when
the question is whether a rule of federal law articulated by this
Court should now be narrowed to reduce the scope of federal
intrusion into the State's administration of criminal justice.
Insofar as modifications of the federal exclusionary Page 462 U. S. 251 rule are concerned, the Illinois courts are bound by this
Court's pronouncements. Cf. Oregon v. Hass, 420 U.
S. 714 , 420 U. S. 719 (1975). I see little point in requiring a litigant to request a
state court to overrule or modify one of this Court's precedents.
Far from encouraging the stability of our precedents, the Court's
proposed practice could well undercut stare decisis. Either the presentation of such issues to the lower courts will be
a completely futile gesture or the lower courts are now invited to
depart from this Court's decisions whenever they conclude such a
modification is in order. [ Footnote
2/6 ]

															The Court correctly notes that Illinois may choose to pursue a
different course with respect to the state exclusionary rule. If
this Court were to formulate a "good faith" exception to the
federal exclusionary rule, the Illinois Supreme Court would be free
to consider on remand whether the state exclusionary rule should be
modified accordingly. The possibility that it might have relied
upon the state exclusionary rule had the "good faith" question been
posed does not constitute independent and adequate state
grounds.

															"The possibility that the state court might have reached the
same conclusion if it had decided the question purely as a matter
of state law does not create an adequate and independent state
ground that relieves this Court of the necessity of considering the
federal question." United Air Lines, Inc. v. Mahin, 410 U.
S. 623 , 410 U. S.
630 -631 (1973); Beecher v. Alabama, 389 U. S. 35 , 389 U. S. 37 , n.
3 (1967); C. Wright, The Law of Federal Courts § 107, pp. 747-748
(4th ed.1983). Nor does having the state court first decide whether
the federal exclusionary rule should be modified -- and
presentation of the federal question does not insure that the
equivalent state law issue will be Page 462 U. S. 252 raised or decided [ Footnote 2/7 ]
-- avoid the unnecessary decision of a federal question. The Court
still must reach a federal question to decide the instant case.
Thus, in today's opinion, the Court eschews modification of the
exclusionary rule in favor of interring the test established by Aguilar v. Texas, 378 U. S. 108 (1964), and Spinelli v. United States, 393 U.
S. 410 (1969). Nor is the exclusionary rule question
avoided -- it is simply deferred until "another day."

															It also appears that the Court, in disposing of the case, does
not strictly follow its own prudential advice. The Illinois Supreme
Court found not only a violation of the Fourth Amendment, but also
of Article I, § 6, of the Illinois Constitution, which also
provides assurance against unreasonable searches and seizures.
Taking the Court's new prudential standards on their own terms, the
Illinois courts should be given the opportunity to consider in the
first instance whether a "totality of the circumstances" test
should replace the more precise rules of Aguilar and Spinelli. The Illinois Supreme Court may decide to retain
the established test for purposes of the State Constitution just as
easily as it could decide to retain an unmodified exclusionary
rule. [ Footnote 2/8 ]

															Finally, the Court correctly notes that a fully developed record
is helpful, if not indispensable, for the decision of many issues.
I too resist the decision of a constitutional question Page 462 U. S. 253 when such guidance is necessary, but the question of whether the
exclusionary rule should be modified is an issue of law which
obviously goes far beyond, and depends little on, the subjective
good faith of the police officers that searched the Gateses'
property. Moreover, the case comes here with a fully developed
record as to the actions of the Bloomingdale, Ill., police. If
further factual development of whether the officers in this case
acted in good faith were important, that issue should logically be
considered on remand, following this Court's statement of the
proper legal standards. [ Footnote
2/9 ]

															The Court's straining to avoid coming to grips with the
exclusionary rule issue today may be hard for the country to
understand -- particularly given earlier statements by some Members
of the Court. [ Footnote 2/10 ] The
question has been fully briefed and argued by the parties and amici curiae, including the United States. [ Footnote 2/11 ] The issue is central to
the enforcement of law and the administration of justice throughout
the Nation. The Court of Appeals for the second largest Federal
Circuit Page 462 U. S. 254 has already adopted such an exception, United States v.
Williams, 622 F.2d 830 (CA5 1980) (en banc), cert.
denied, 449 U.S. 1127 (1981), and the new Eleventh Circuit is
presumably bound by its decision. Several Members of this Court
have for some time expressed the need to consider modifying the
exclusionary rule, ante at 462 U. S. 224 ,
and Congress as well has been active in exploring the question. See The Exclusionary Rule Bills, Hearings on S. 101, S.
751, and S.1995 before the Subcommittee on Criminal Law of the
Senate Committee on the Judiciary, 97th Cong., 1st and 2d Sess.
(1981-1982). At least one State has already enacted a good faith
exception. Colo.Rev.Stat. § 16-3-308 (Supp.1982). Of course, if
there is a jurisdictional barrier to deciding the issue, none of
these considerations is relevant. But if no such procedural
obstacle exists, I see it as our responsibility to end the
uncertainty and decide whether the rule will be modified. The
question of whether probable cause existed for the issuance of a
warrant and whether the evidence seized must be excluded in this
case should follow our reconsideration of the framework by which
such issues, as they arise from the Fourth Amendment, are to be
handled. II A The exclusionary rule is a remedy adopted by this Court to
effectuate the Fourth Amendment right of citizens "to be secure in
their persons, houses, papers, and effects, against unreasonable
searches and seizures. . . ." Although early opinions suggested
that the Constitution required exclusion of all illegally obtained
evidence, the exclusionary rule "has never been interpreted to
proscribe the introduction of illegally seized evidence in all
proceedings or against all persons." Stone v. Powell, 428
U.S. at 428 U. S. 486 .
Because of the inherent trustworthiness of seized tangible evidence
and the resulting social costs from its loss through suppression,
application Page 462 U. S. 255 of the exclusionary rule has been carefully "restricted to those
areas where its remedial objectives are thought most efficaciously
served." United States v. Calandra, 414 U.
S. 338 , 414 U. S. 348 (1974). Even at criminal trials the exclusionary rule has not been
applied indiscriminately to ban all illegally obtained evidence
without regard to the costs and benefits of doing so. Infra at 462 U. S.
256 -257. These developments, born of years of experience
with the exclusionary rule in operation, forcefully suggest that
the exclusionary rule be more generally modified to permit the
introduction of evidence obtained in the reasonable good faith
belief that a search or seizure was in accord with the Fourth
Amendment.

															This evolvement in the understanding of the proper scope of the
exclusionary rule embraces several lines of cases. First, standing
to invoke the exclusionary rule has been limited to situations
where the government seeks to use such evidence against the victim
of the unlawful search. Brown v. United States, 411 U. S. 223 (1973); Alderman v. United States, 394 U.
S. 165 (1969); Wong Sun v. United States, 371 U. S. 471 , 371 U. S.
491 -492 (1963); Rakas v. Illinois, 439 U.
S. 128 (1978).

															Second, the rule has not been applied in proceedings other than
the trial itself. In United States v. Calandra, supra, the
Court refused to extend the rule to grand jury proceedings.

															"Any incremental deterrent effect which might be achieved by
extending the rule to grand jury proceedings is uncertain at best.
. . . We therefore decline to embrace a view that would achieve a
speculative and undoubtedly minimal advance in the deterrence of
police misconduct at the expense of substantially impeding the role
of the grand jury."

															414 U.S. at 414 U. S.
351 -352. Similarly, in United States v. Janis, 428 U. S. 433 (1976), the exclusionary rule was not extended to forbid the use in
federal civil proceedings of evidence illegally seized by state
officials, since the likelihood of deterring unlawful police
conduct was not sufficient to outweigh the social costs imposed by
the exclusion. Page 462 U. S. 256 Third, even at a criminal trial, the same analysis has led us to
conclude that the costs of excluding probative evidence outweighed
the deterrence benefits in several circumstances. We have refused
to prohibit the use of illegally seized evidence for the purpose of
impeaching a defendant who testifies in his own behalf. United
States v. Havens, 446 U. S. 620 (1980); Walder v. United States, 347 U. S.
62 (1954). We have also declined to adopt a " per
se or but for' rule" that would make inadmissible any
evidence which comes to light through a chain of causation that
began with an illegal arrest. Brown v. Illinois, 422 U. S. 590 , 422 U. S. 603 (1975). And we have held that testimony of a live witness may be
admitted, notwithstanding that the testimony was derived from a
concededly unconstitutional search. United States v.
Ceccolini, 435 U. S. 268 (1978). Nor is exclusion required when law enforcement agents act
in good faith reliance upon a statute or ordinance that is
subsequently held to be unconstitutional. United States v.
Peltier, 422 U. S. 531 (1975); Michigan v. DeFillippo, 443 U. S.
31 (1979). [ Footnote
2/12 ] Cf. United States v. Caceres, 440 U.
S. 741 , 440 U. S.
754 -757 (1979) (exclusion not Page 462 U. S. 257 required of evidence tainted by violation of an executive
department's rules concerning electronic eavesdropping).

															A similar balancing approach is employed in our decisions
limiting the scope of the exclusionary remedy for Fifth Amendment
violations, Oregon v. Hass, 420 U.
S. 714 (1975); Harris v. New York, 401 U.
S. 222 (1971); Michigan v. Tucker, 417 U.
S. 433 (1974), and our cases considering whether Fourth
Amendment decisions should be applied retroactively, United
States v. Peltier, supra, at 422 U. S.
538 -539; Williams v. United States, 401 U. S. 646 , 401 U. S.
654 -655 (1971) (plurality opinion); Dest v. United
States, 394 U. S. 244 , 394 U. S.
249 -250 (1969); Linkletter v. Walker, 381 U. S. 618 , 381 U. S.
636 -639 (1965). But see United States v.
Johnson, 457 U. S. 537 (1982).

															These cases reflect that the exclusion of evidence is not a
personal constitutional right, but a remedy, which, like all
remedies, must be sensitive to the costs and benefits of its
imposition. The trend and direction of our exclusionary rule
decisions indicate not a lesser concern with safeguarding the
Fourth Amendment but a fuller appreciation of the high costs
incurred when probative, reliable evidence is barred because of
investigative error. The primary cost, of course, is that the
exclusionary rule interferes with the truth-seeking function of a
criminal trial by barring relevant and trustworthy evidence.
[ Footnote 2/13 ] We will never
know how many guilty defendants go free as a result of the rule's
operation. But any rule of evidence that denies the jury access to
clearly probative and reliable evidence must bear a heavy burden of
justification, Page 462 U. S. 258 and must be carefully limited to the circumstances in which it
will pay its way by deterring official lawlessness. I do not
presume that modification of the exclusionary rule will, by itself,
significantly reduce the crime rate -- but that is no excuse for
indiscriminate application of the rule.

															The suppression doctrine entails other costs as well. It would
be surprising if the suppression of evidence garnered in good
faith, but by means later found to violate the Fourth Amendment,
did not deter legitimate as well as unlawful police activities. To
the extent the rule operates to discourage police from reasonable
and proper investigative actions, it hinders the solution and even
the prevention of crime. A tremendous burden is also placed on the
state and federal judicial systems. One study reveals that
one-third of federal defendants going to trial file Fourth
Amendment suppression motions, and 70% to 90% of these involve
formal hearings. General Accounting Office, Comptroller General of
the United States, Impact of the Exclusionary Rule on Federal
Criminal Prosecutions 10 (1979).

															The rule also exacts a heavy price in undermining public
confidence in the reasonableness of the standards that govern the
criminal justice system.

															"[A]lthough the [exclusionary] rule is thought to deter unlawful
police activity in part through the nurturing of respect for Fourth
Amendment values, if applied indiscriminately, it may well have the
opposite effect of generating disrespect for the law and the
administration of justice." Stone v. Powell, 428 U.S. at 428 U. S.
490 -491. As JUSTICE POWELL observed in Stone v.
Powell, supra, at 428 U. S.
490 :

															"The disparity in particular cases between the error committed
by the police officer and the windfall afforded a guilty defendant
by application of the rule is contrary to the idea of
proportionality that is essential to the concept of justice."

															For these reasons, "application of the [exclusionary] rule has
been restricted to those areas where its remedial objectives are
thought most efficaciously served." United States Page 462 U. S. 259 v. Calandra, 414 U.S. at 414 U. S. 348 .
[ Footnote 2/14 ] The reasoning of
our recent cases strongly suggests that there is insufficient
justification to suppress evidence at a criminal trial which was
seized in the reasonable belief that the Fourth Amendment was not
violated. The deterrent effect of the exclusionary rule has never
been established by empirical evidence, despite Page 462 U. S. 260 repeated attempts. United States v. Janis, 428 U.S. at 428 U. S.
449 -453; Irvine v. California, 347 U.
S. 128 , 347 U. S. 136 (1954). But accepting that the rule deters some police misconduct,
it is apparent as a matter of logic that there is little if any
deterrence when the rule is invoked to suppress evidence obtained
by a police officer acting in the reasonable belief that his
conduct did not violate the Fourth Amendment. As we initially
observed in Michigan v. Tucker, 417 U.S. at 417 U. S. 447 ,
and reiterated in United States v. Peltier, 422 U.S. at 422 U. S.
539 :

															"'The deterrent purpose of the exclusionary rule necessarily
assumes that the police have engaged in willful, or at the very
least negligent, conduct which has deprived the defendant of some
right. By refusing to admit evidence gained as a result of such
conduct, the courts hope to instill in those particular
investigating officers, or in their future counterparts, a greater
degree of care toward the rights of an accused. Where the official
action was pursued in complete good faith, however, the deterrence
rationale loses much of its force.'"

															The Court in Peltier continued, id. at 422 U. S.
542 :

															"If the purpose of the exclusionary rule is to deter unlawful
police conduct, then evidence obtained from a search should be
suppressed only if it can be said that the law enforcement officer
had knowledge, or may properly be charged with knowledge, that the
search was unconstitutional under the Fourth Amendment." See also United States v. Janis, supra, at 428 U. S. 459 ,
n. 35 ("[T]he officers here were clearly acting in good faith . . .
a factor that the Court has recognized reduces significantly the
potential deterrent effect of exclusion"). The deterrent value of
the exclusionary sanction is most effective when officers engage in
searches and seizures under circumstances "so lacking in indicia of
probable cause as to render official belief in its existence
entirely unreasonable." Brown v. Illinois, 422 U.S. at 422 U. S.
610 -611 (POWELL, J., concurring in part). On the Page 462 U. S. 261 other hand, when officers perform their tasks in the good faith
belief that their action comported with constitutional
requirements, the deterrent function of the exclusionary rule is so
minimal, if not nonexistent, that the balance clearly favors the
rule's modification. [ Footnote
2/15 ] Page 462 U. S. 262 B There are several types of Fourth Amendment violations that may
be said to fall under the rubric of "good faith."

															"[T]here will be those occasions where the trial or appellate
court will disagree on the issue of probable cause, no matter how
reasonable the grounds for arrest appeared to the officer and
though reasonable men could easily differ on the question. It also
happens that after the events at issue have occurred, the law may
change, dramatically or ever so slightly, but in any event
sufficiently to require the trial judge to hold that there was not
probable cause to make the arrest and to seize the evidence offered
by the prosecution. . . ." Stone v. Powell, 428 U.S. at 428 U. S.
539 -540 (WHITE, J., dissenting). The argument for a good
faith exception is strongest, however, when law enforcement
officers have reasonably relied on a judicially issued search
warrant.

															This Court has never set forth a rationale for applying the
exclusionary rule to suppress evidence obtained pursuant to a
search warrant; it has simply done so without considering whether
Fourth Amendment interests will be advanced. It is my view that
they generally will not be. When officers have dutifully obtained a
search warrant from a judge or magistrate, and execute the warrant
as directed by its terms, exclusion of the evidence thus obtained
cannot be expected to deter future reliance on such warrants. The
warrant is prima facie proof that the officers acted
reasonably in conducting the search or seizure; "[o]nce the warrant
issues, there is literally nothing more that the policeman can do
in seeking to comply with the law." Stone v. Powell,
supra, at 428 U. S. 498 (BURGER, C.J., concurring). [ Footnote
2/16 ] As JUSTICE STEVENS Page 462 U. S. 263 put it in writing for the Court in United States v.
Ross, 456 U. S. 798 , 456 U. S. 823 ,
n. 32 (1982): "[A] warrant issued by a magistrate normally suffices
to establish" that a law enforcement officer has "acted in good
faith in conducting the search." Nevertheless, the warrant may be
invalidated because of a technical defect or because, as in this
case, the judge issued a warrant on information later determined to
fall short of probable cause. Excluding evidence for these reasons
can have no possible deterrent effect on future police conduct,
unless it is to make officers less willing to do their duty.
Indeed, applying the exclusionary rule to warrant searches may well
reduce incentives for police to utilize the preferred warrant
procedure when a warrantless search may be permissible under one of
the established exceptions to the warrant requirement. See
ante at 462 U. S. 236 ; Brown v. Illinois, 422 U.S. at 422 U. S. 611 ,
and n. 3 (POWELL, J., concurring in part); P. Johnson, New
Approaches to Enforcing the Fourth Amendment 11 (unpublished paper,
1978). See also United States v. United States District
Court, 407 U. S. 297 , 407 U. S.
316 -317 (1972); United States v. Ventresca, 380 U. S. 102 , 380 U. S.
106 -107 (1965).

															Opponents of the proposed "reasonable belief" exception suggest
that such a modification would allow magistrates and judges to
flout the probable cause requirements in issuing warrants. This is
a novel concept: the exclusionary rule was adopted to deter
unlawful searches by police, not to punish the errors of
magistrates and judges. Magistrates must be neutral and detached
from law enforcement operations, and I would not presume that a
modification of the exclusionary rule will lead magistrates to
abdicate their responsibility to apply the law. [ Footnote 2/17 ] In any event, I would apply the
exclusionary Page 462 U. S. 264 rule when it is plainly evident that a magistrate or judge had
no business issuing a warrant. See, e.g., Aguilar v.
Texas, 378 U. S. 108 (1964); Nathanson v. United States, 290 U. S.
41 (1933). Similarly, the good faith exception would not
apply if the material presented to the magistrate or judge is false
or misleading, Franks v. Delaware, 438 U.
S. 154 (1978), or so clearly lacking in probable cause
that no well-trained officer could reasonably have thought that a
warrant should issue.

															Another objection is that a reasonable belief exception will
encompass all searches and seizures on the frontier of the Fourth
Amendment and that such cases will escape review on the question of
whether the officer's action was permissible, denying needed
guidance from the courts and freezing Fourth Amendment law in its
present state. These fears are unjustified. The premise of the
argument is that a court must first decide the reasonable belief
issue before turning to the question of whether a Fourth Amendment
violation has occurred. I see no need for such an inflexible
practice. When a Fourth Amendment case presents a novel question of
law whose resolution is necessary to guide future action by law
enforcement officers and magistrates, there is sufficient reason
for the Court to decide the violation issue before turning to the
good faith question. Indeed, it may be difficult to Page 462 U. S. 265 determine whether the officers acted reasonably until the Fourth
Amendment issue is resolved. [ Footnote 2/18 ] In other circumstances, however, a
suppression motion poses no Fourth Amendment question of broad
import -- the issue is simply whether the facts in a given case
amounted to probable cause in these cases, it would be prudent for
a reviewing court to immediately turn to the question of whether
the officers acted in good faith. Upon finding that they had, there
would generally be no need to consider the probable cause question.
I doubt that our Fourth Amendment jurisprudence would suffer
thereby. It is not entirely clear to me that the law in this area
has benefited from the constant pressure of fully litigated
suppression motions. The result usually has been that initially
bright-line rules have disappeared in a sea of ever-finer
distinctions. Moreover, there is much to be said for having Fourth
Amendment jurisprudence Page 462 U. S. 266 evolve in part, albeit perhaps at a slower pace, in other
settings. [ Footnote 2/19 ]

															Finally, it is contended that a good faith exception will be
difficult to apply in practice. This concern appears grounded in
the assumption that courts would inquire into the subjective belief
of the law enforcement officers involved. I would eschew such
investigations.

															"[S]ending state and federal courts on an expedition into the
minds of police officers would produce a grave and fruitless
misallocation of judicial resources." Massachusetts v. Painten, 389 U.
S. 560 , 389 U. S. 565 (1968) (WHITE, J., dissenting). Moreover, "[s]ubjective intent
alone . . . does not make otherwise lawful conduct illegal or
unconstitutional." Scott v. United States, 436 U.
S. 128 , 436 U. S. 136 (1978). Just last Term, we modified the qualified immunity public
officials enjoy in suits seeking damages against federal officials
for alleged deprivations of constitutional rights, eliminating the
subjective component of the standard. See Harlow v.
Fitzgerald, 457 U. S. 800 (1982). Although Page 462 U. S. 267 searches pursuant to a warrant will rarely require any deep
inquiry into reasonableness, I would measure the reasonableness of
a particular search or seizure only by objective standards. Even
for warrantless searches, the requirement should be no more
difficult to apply than the closely related good faith test which
governs civil suits under 42 U.S.C. § 1983. In addition, the burden
will likely be offset by the reduction in the number of cases which
will require elongated considerations of the probable cause
question, and will be greatly outweighed by the advantages in
limiting the bite of the exclusionary rule to the field in which it
is most likely to have its intended effects. III Since a majority of the Court deems it inappropriate to address
the good faith issue, I briefly address the question that the Court
does reach -- whether the warrant authorizing the search and
seizure of respondents' car and home was constitutionally valid.
Abandoning the "two-pronged test" of Aguilar v. Texas, 378 U. S. 108 (1964), and Spinelli v. United States, 393 U.
S. 410 (1969), the Court upholds the validity of the
warrant under a new "totality of the circumstances" approach.
Although I agree that the warrant should be upheld, I reach this
conclusion in accordance with the Aguilar-Spinelli framework. A For present purposes, the Aguilar-Spinelli rules can be
summed up as follows. First, an affidavit based on an informant's
tip, standing alone, cannot provide probable cause for issuance of
a warrant unless the tip includes information that apprises the
magistrate of the informant's basis for concluding that the
contraband is where he claims it is (the "basis of knowledge"
prong), and the affiant informs the magistrate of his basis for
believing that the informant is credible (the "veracity" prong). Aguilar, supra, at 378 U. S.
114 ; Page 462 U. S. 268 Spinelli, supra, at 393 U. S.
412 -413, 416. [ Footnote
2/20 ] Second, if a tip fails under either or both of the two
prongs, probable cause may yet be established by independent police
investigatory work that corroborates the tip to such an extent that
it supports

															"both the inference that the informer was generally trustworthy
and that he made his charge . . . on the basis of information
obtained in a reliable way." Spinelli, supra, at 393 U. S. 417 .
In instances where the officers rely on corroboration, the ultimate
question is whether the corroborated tip "is as trustworthy as a
tip which would pass Aguilar's tests without independent
corroboration." 393 U.S. at 393 U. S.
415 .

															In the present case, it is undisputed that the anonymous tip, by
itself, did not furnish probable cause. The question is whether
those portions of the affidavit describing the results of the
police investigation of the respondents, when considered in light
of the tip,

															"would permit the suspicions engendered by the informant's
report to ripen into a judgment that a crime was probably being
committed." Spinelli, supra, at 393 U. S. 418 .
The Illinois Supreme Court concluded that the corroboration was
insufficient to permit such a ripening. 85 Ill. 2d
376 , 387, 423 N.E.2d
887 , 892 (1981). The court reasoned as follows:

															"[T]he nature of the corroborating evidence in this case would
satisfy neither the 'basis of knowledge' nor the Page 462 U. S. 269 'veracity' prong of Aguilar. Looking to the affidavit
submitted as support for Detective Mader's request that a search
warrant issue, we note that the corroborative evidence here was
only of clearly innocent activity. Mader's independent
investigation revealed only that Lance and Sue Gates lived on
Greenway Drive; that Lance Gates booked passage on a flight to
Florida; that upon arriving he entered a room registered to his
wife; and that he and his wife left the hotel together by car. The
corroboration of innocent activity is insufficient to support a
finding of probable cause." Id. at 390, 423 N.E.2d at 893.

															In my view, the lower court's characterization of the Gateses'
activity here as totally "innocent" is dubious. In fact, the
behavior was quite suspicious. I agree with the Court, ante at 462 U. S. 243 ,
that Lance Gates' flight to West Palm Beach, an area known to be a
source of narcotics, the brief overnight stay in a motel, and
apparent immediate return north, suggest a pattern that trained law
enforcement officers have recognized as indicative of illicit
drug-dealing activity. [ Footnote
2/21 ]

															Even, however, had the corroboration related only to completely
innocuous activities, this fact alone would not preclude the
issuance of a valid warrant. The critical issue is not whether the
activities observed by the police are innocent or suspicious.
Instead, the proper focus should be on whether the actions of the
suspects, whatever their nature, give rise to an inference that the
informant is credible and that he obtained his information in a
reliable manner.

															Thus, in Draper v. United States, 358 U.
S. 307 (1959), an informant stated on September 7 that
Draper would be carrying narcotics when he arrived by train in
Denver on the morning of September 8 or September 9. The informant
also provided the police with a detailed physical description Page 462 U. S. 270 of the clothes Draper would be wearing when he alighted from the
train. The police observed Draper leaving a train on the morning of
September 9, and he was wearing the precise clothing described by
the informant. The Court held that the police had probable cause to
arrest Draper at this point, even though the police had seen
nothing more than the totally innocent act of a man getting off a
train carrying a briefcase. As we later explained in Spinelli, the important point was that the corroboration
showed both that the informant was credible, i.e., that he
"had not been fabricating his report out of whole cloth," Spinelli, 393 U.S. at 393 U. S. 417 ,
and that he had an adequate basis of knowledge for his allegations,
"since the report was of the sort which, in common experience, may
be recognized as having been obtained in a reliable way." Id. at 393 U. S.
417 -418. The fact that the informant was able to
predict, two days in advance, the exact clothing Draper would be
wearing dispelled the possibility that his tip was just based on
rumor or "an offhand remark heard at a neighborhood bar." Id. at 393 U. S. 417 .
Probably Draper had planned in advance to wear these specific
clothes so that an accomplice could identify him. A clear inference
could therefore be drawn that the informant was either involved in
the criminal scheme himself or that he otherwise had access to
reliable, inside information. [ Footnote 2/22 ] Page 462 U. S. 271 As in Draper, the police investigation in the present
case satisfactorily demonstrated that the informant's tip was as
trustworthy as one that would, alone, satisfy the Aguilar tests. The tip predicted that Sue Gates would drive to Florida,
that Lance Gates would fly there a few days after May 3, and that
Lance would then drive the car back. After the police corroborated
these facts, [ Footnote 2/23 ] the
judge could reasonably have inferred, as he apparently did, that
the informant, who had specific knowledge of these unusual travel
plans, did not make up his story, and that he obtained his
information in a reliable way. It is theoretically possible, as
respondents insist, that the tip could have been supplied by a
"vindictive travel agent" and that the Gateses' activities,
although unusual, might not have been unlawful. [ Footnote 2/24 ] But Aguilar and Spinelli, like our other cases, do not require that
certain guilt be established before a warrant may properly be
issued. "[O]nly the probability, and not a prima facie showing, Page 462 U. S. 272 of criminal activity is the standard of probable cause." Spinelli, supra, at 393 U. S. 419 (citing Beck v. Ohio, 379 U. S. 89 , 379 U. S. 96 (1964)). I therefore conclude that the judgment of the Illinois
Supreme Court invalidating the warrant must be reversed. B The Court agrees that the warrant was valid, but, in the process
of reaching this conclusion, it overrules the Aguilar-Spinelli tests and replaces them with a "totality
of the circumstances" standard. As shown above, it is not at all
necessary to overrule Aguilar-Spinelli in order to reverse
the judgment below. Therefore, because I am inclined to believe
that, when applied properly, the Aguilar-Spinelli rules
play an appropriate role in probable cause determinations, and
because the Court's holding may foretell an evisceration of the
probable cause standard, I do not join the Court's holding.

															The Court reasons, ante at 462 U. S. 233 ,
that the "veracity" and "basis of knowledge" tests are not
independent, and that a deficiency as to one can be compensated for
by a strong showing as to the other. Thus, a finding of probable
cause may be based on a tip from an informant "known for the
unusual reliability of his predictions" or from "an unquestionably
honest citizen," even if the report fails thoroughly to set forth
the basis upon which the information was obtained. Ibid. If this is so, then it must follow a fortiori that "the
affidavit of an officer, known by the magistrate to be honest and
experienced, stating that [contraband] is located in a certain
building" must be acceptable. Spinelli, 393 U.S. at 393 U. S. 424 (WHITE, J., concurring). It would be "quixotic" if a similar
statement from an honest informant, but not one from an honest
officer, could furnish probable cause. Ibid. But we have
repeatedly held that the unsupported assertion or belief of an
officer does not satisfy the probable cause requirement. See,
e.g., Whiteley v. Warden, 401 U. S. 560 , 401 U. S.
564 -565 Page 462 U. S. 273 (1971); Jones v. United States, 362 U.
S. 257 , 362 U. S. 269 (1960); Nathanson v. United States, 290 U. S.
41 (1933). [ Footnote
2/25 ] Thus, this portion of today's holding can be read as
implicitly rejecting the teachings of these prior holdings.

															The Court may not intend so drastic a result. Indeed, the Court
expressly reaffirms, ante at 462 U. S. 239 ,
the validity of cases such as Nathanson that have held
that, no matter how reliable the affiant-officer may be, a warrant
should not be issued unless the affidavit discloses supporting
facts and circumstances. The Court limits these cases to situations
involving affidavits containing only "bare conclusions," and holds
that, if an affidavit contains anything more, it should be left to
the issuing magistrate to decide, based solely on "practical[ity]"
and "common sense," whether there is a fair probability that
contraband will be found in a particular place. Ante at 462 U. S.
238 -239.

															Thus, as I read the majority opinion, it appears that the
question whether the probable cause standard is to be diluted is
left to the common sense judgments of issuing magistrates. I am
reluctant to approve any standard that does not expressly require,
as a prerequisite to issuance of a warrant, some showing of facts
from which an inference may be drawn that the informant is credible
and that his information was obtained in a reliable way. The Court
is correctly concerned with the fact that some lower courts have
been applying Aguilar-Spinelli in an unduly rigid manner.
[ Footnote 2/26 ] I believe,
however, that with clarification of the rule of corroborating Page 462 U. S. 274 information, the lower courts are fully able to properly
interpret Aguilar-Spinelli and avoid such unduly rigid
applications. I may be wrong; it ultimately may prove to be the
case that the only profitable instruction we can provide to
magistrates is to rely on common sense. But the question whether a
particular anonymous tip provides the basis for issuance of a
warrant will often be a difficult one, and I would at least attempt
to provide more precise guidance by clarifying Aguilar-Spinelli and the relationship of those cases with Draper before totally abdicating our responsibility in
this area. Hence, I do not join the Court's opinion rejecting the Aguilar-Spinelli rules.

															[ Footnote 2/1 ] See, e.g., Eddings v. Oklahoma, 455 U.
S. 104 (1982); Wood v. Georgia, 450 U.
S. 261 (1981); Vachon v. New Hampshire, 414 U. S. 478 (1974) (per curiam). Of course, to the extent these cases were
correctly decided, they indicate a fortiori that the
exclusionary rule issue in this case is properly before us.

															[ Footnote 2/2 ]

															The Court has previously relied on issues and arguments not
raised in the state court below in order to dispose of a federal
question that was properly raised. In Stanley v. Illinois, 405 U. S. 645 , 405 U. S. 658 (1972), the Court held that unmarried fathers could not be denied a
hearing on parental fitness that was afforded other Illinois
parents. Although this issue was not presented in the Illinois
courts, the Court found that it could properly be considered:

															"we dispose of the case on the constitutional premise raised
below, reaching the result by a method of analysis readily
available to the state court. For the same reason, the strictures
of Cardinale v. Louisiana, 394 U. S.
437 (1969), and Hill v. California, 401 U. S.
797 (1971), have been fully observed." Id. at 405 U. S. 658 ,
n. 10. The dissent argued that the Court was deciding a due process
claim, instead of an equal protection one, but there was no
suggestion that it mattered at all that the Court had relied on a
different type of equal protection argument.

															[ Footnote 2/3 ]

															As the Court explains, ante at 462 U. S. 220 ,
n. 2, in Dewey, the plaintiff in error argued only that
the imposition of personal liability against him violated the Due
Process Clause of the Fourteenth Amendment, because he had not
received personal notice of the assessment proceedings. In this
Court, the plaintiff in error sought to raise a takings argument
for the first time. The Court declined to pass on the issue
because, although arising from a single factual occurrence, the two
claims "are not in anywise necessarily connected." 173 U.S. at 173 U. S.
198 .

															[ Footnote 2/4 ]

															The Court relies on these cases for the surprising assertion
that the Fourth Amendment and exclusionary rule questions are
"distinct." I had understood the very essence of Rakas v.
Illinois, 439 U. S. 128 (1978), to be that standing to seek exclusion of evidence could not
be divorced from substantive Fourth Amendment rights. Past
decisions finding that the remedy of exclusion is not always
appropriate upon the finding of a Fourth Amendment violation
acknowledge the close relationship of the issues. For example, in United States v. Ceccolini, it was said:

															"The constitutional question under the Fourth Amendment was
phrased in Wong Sun v. United States, 371 U. S.
471 (1963), as whether"

															"the connection between the lawless conduct of the police and
the discovery of the challenged evidence has 'become so attenuated
as to dissipate the taint.'"

															435 U.S. at 435 U. S.
273 -274. It is also surprising to learn that the issues
in Stone v. Powell are "distinct" from the Fourth
Amendment.

															[ Footnote 2/5 ]

															Consider the full context of the statement in McGoldrick v.
Compagnie Generale Transatlantique, 309 U.
S. 430 , 309 U. S. 434 (1940):

															"In cases coming here from state courts in which a state statute
is assailed as unconstitutional, there are reasons of peculiar
force which should lead us to refrain from deciding questions not
presented or decided in the highest court of the state whose
judicial action we are called upon to review. Apart from the
reluctance with which every court should proceed to set aside
legislation as unconstitutional on grounds not properly presented,
due regard for the appropriate relationship of this Court to state
courts requires us to decline to consider and decide questions
affecting the validity of state statutes not urged or considered
there. It is for these reasons that this Court, where the
constitutionality of a statute has been upheld in the state court,
consistently refuses to consider any grounds of attack not raised
or decided in that court."

															[ Footnote 2/6 ]

															The Court observes that, "although the Illinois courts applied
the federal exclusionary rule, there was never any real
contest' upon the point." Ante at 462 U. S. 223 .
But the proper forum for a "real contest" on the continued vitality
of the exclusionary rule that has developed from our decisions in Weeks v. United States, 232 U. S. 383 (1914), and Mapp v. Ohio, 367 U.
S. 643 (1961), is this Court. [ Footnote 2/7 ]

															Nor is there any reason for the Illinois courts to decide that
question in advance of this Court's decision on the federal
exclusionary rule. Until the federal rule is modified, the state
law question is entirely academic. The state courts should not be
expected to render such purely advisory decisions.

															[ Footnote 2/8 ]

															Respondents press this very argument. Brief for Respondents
24-27; Brief for Respondents on Reargument 6. Of course, under
traditional principles, the possibility that the state court might
reach a different conclusion in interpreting the State Constitution
does not make it improper for us to decide the federal issue. Delaware v. Prouse, 440 U. S. 648 , 440 U. S.
651 -653 (1979); Zacchini v. Scripps-Howard
Broadcasting Co., 433 U. S. 562 , 433 U. S. 568 (1977).

															[ Footnote 2/9 ]

															It also should be noted that the requirement that the good faith
issue be presented to the Illinois courts has little to do with
whether the record is complete. I doubt that the raising of the
good faith issue below would have been accompanied by any different
record. And this Court may dismiss a writ of certiorari as
improvidently granted when the record makes decision of a federal
question unwise. See, e.g., Minnick v. California Dept. of
Corrections, 452 U. S. 105 (1981).

															[ Footnote 2/10 ]

															In California v. Minjares, 443 U.
S. 916 , 928 (1979) (REHNQUIST, J., joined by BURGER,
C.J., dissenting from the denial of stay), the author of today's
opinion for the Court urged that the parties be directed to brief
whether the exclusionary rule should be retained. In Minjares, like this case, respondents had raised a Fourth
Amendment claim, but petitioners had not attacked the validity of
the exclusionary rule in the state court. See also Robbins v.
California, 453 U. S. 420 , 453 U. S. 437 (1981) (REHNQUIST, J., dissenting) (advocating overruling of Mapp v. Ohio, supra ).

															[ Footnote 2/11 ]

															Ironically, in Mapp v. Ohio, supra, petitioners did not
ask the Court to partially overrule Wolf v. Colorado, 338 U. S. 25 (1949). The sole argument to apply the exclusionary rule to the
States is found in a single paragraph in an amicus brief
filed by the American Civil Liberties Union.

															[ Footnote 2/12 ]

															To be sure, Peltier and DeFillippo did not
modify the exclusionary rule itself. Peltier held that Almeida-Sanchez v. United States, 413 U.
S. 266 (1973), was not to be given retroactive effect; DeFillippo upheld the validity of an arrest made in good
faith reliance on an ordinance subsequently declared
unconstitutional. The effect of these decisions, of course, was
that evidence was not excluded because of the officer's reasonable
belief that he was acting lawfully, and the Court's reasoning, as I
discuss infra, at 462 U. S. 260 -261, leads inexorably to the more general
modification of the exclusionary rule I favor. Indeed, JUSTICE
BRENNAN recognized this in his dissent in Peltier, 422
U.S. at 422 U. S.
551 -552.

															I recognize that we have held that the exclusionary rule
required suppression of evidence obtained in searches carried out
pursuant to statutes, not previously declared unconstitutional,
which purported to authorize the searches in question without
probable cause and without a valid warrant. See, e.g., Torres
v. Puerto Rico, 442 U. S. 465 (1979); Almeida-Sanchez v. United States, supra; Sibron v. New
York, 392 U. S. 40 (1968); Berger v. New York, 388 U. S.
41 (1967). The results in these cases may well be
different under a "good faith" exception to the exclusionary
rule.

															[ Footnote 2/13 ]

															The effects of the exclusionary rule are often felt before a
case reaches trial. A recent study by the National Institute of
Justice of felony arrests in California during the years 1976-1979
"found a major impact of the exclusionary rule on state
prosecutions." National Institute of Justice, The Effects of the
Exclusionary Rule: A Study in California 2 (1982). The study found
that 4.8% of the more than 4,000 felony cases declined for
prosecution were rejected because of search and seizure problems.
The exclusionary rule was found to have a particularly pronounced
effect in drug cases; prosecutors rejected approximately 30% of all
felony drug arrests because of search and seizure problems.

															[ Footnote 2/14 ]

															Our decisions applying the exclusionary rule have referred to
the "imperative of judicial integrity," Elkins v. United
States, 364 U. S. 206 , 364 U. S. 222 (1960), although recent opinions of the Court make clear that the
primary function of the exclusionary rule is to deter violations of
the Fourth Amendment, Stone v. Powell, 428 U.S. at 428 U. S. 486 ; United States v. Janis, 428 U. S. 433 , 428 U. S. 446 (1976); United States v. Calandra, 414 U.S. at 414 U. S. 348 .
I do not dismiss the idea that the integrity of the courts may be
compromised when illegally seized evidence is admitted, but I am
convinced that the force of the argument depends entirely on the
type of search or seizure involved. At one extreme, there are
lawless invasions of personal privacy that shock the conscience,
and the admission of evidence so obtained must be suppressed as a
matter of due process, entirely aside from the Fourth Amendment. See, e.g., Rochin v. California, 342 U.
S. 165 (1952). Also deserving of exclusionary treatment
are searches and seizures perpetrated in intentional and flagrant
disregard of Fourth Amendment principles. But the question of
exclusion must be viewed through a different lens when a Fourth
Amendment violation occurs because the police have reasonably erred
in assessing the facts, mistakenly conducted a search authorized
under a presumably valid statute, or relied in good faith upon a
warrant not supported by probable cause. In these circumstances,
the integrity of the courts is not implicated. The violation of the
Fourth Amendment is complete before the evidence is admitted.
Thus,

															"[t]he primary meaning of 'judicial integrity' in the context of
evidentiary rules is that the courts must not commit or encourage
violations of the Constitution." United States v. Janis, supra, at 428 U. S. 458 ,
n. 35. Cf. United States v. Peltier, 422 U.
S. 531 , 422 U. S. 537 (1975) ("The teaching of these retroactivity cases is that, if the
law enforcement officers reasonably believed in good faith that
evidence they had seized was admissible at trial, the imperative of judicial integrity' is not offended by the
introduction into evidence of that material even if decisions
subsequent to the search or seizure have broadened the exclusionary
rule to encompass evidence seized in that manner"). I am content
that the interests in judicial integrity run along with, rather
than counter to, the deterrence concept, and that to focus upon the
latter is to promote, not denigrate, the former. [ Footnote 2/15 ]

															It has been suggested that the deterrence function of the
exclusionary rule has been understated by viewing the rule as aimed
at special deterrence, when, in fact, the exclusionary rule is
directed at "affecting the wider audience of law enforcement
officials and society at large." 1 W. LaFave, Search and Seizure 6
(1983 Supp.). See also Mertens & Wasserstrom, The Good
Faith Exception to the Exclusionary Rule: Deregulating the Police
and Derailing the Law, 70 Geo.L.J. 365, 399-401 (1981). I agree
that the exclusionary rule's purpose is not only, or even
primarily, to deter the individual police officer involved in the
instant case. It appears that this objection assumes that the
proposed modification of the exclusionary rule will turn only on
the subjective "good faith" of the officer. Grounding the
modification in objective reasonableness, however, retains the
value of the exclusionary rule as an incentive for the law
enforcement profession as a whole to conduct themselves in accord
with the Fourth Amendment. Dunaway v. New York, 442 U. S. 200 , 442 U. S. 221 (1979) (STEVENS, J., concurring).

															Indeed, the present indiscriminate application of the
exclusionary rule may hinder the educative and deterrent function
of the suppression remedy.

															"Instead of disciplining their employees, police departments
generally have adopted the attitude that the courts cannot be
satisfied, that the rules are hopelessly complicated and subject to
change, and that the suppression of evidence is the court's
problem, and not the departments'."

															Kaplan, The Limits of the Exclusionary Rule, 26 Stan.L.Rev.
1027, 1050 (1974). If evidence is suppressed only when a law
enforcement officer should have known that he was violating the
Fourth Amendment, police departments may look more seriously at the
officer's misconduct when suppression is invoked. Moreover, by
providing that evidence gathered in good faith reliance on a
reasonable rule will not be excluded, a good faith exception
creates an incentive for police departments to formulate rules
governing activities of officers in the search and seizure area.
Many commentators, including proponents of the exclusionary
sanction, recognize that the formulation of such rules by police
departments, and the training necessary to implement these
guidelines in practice, are perhaps the most effective means of
protecting Fourth Amendment rights. See K. Davis,
Discretionary Justice (1969); McGowan, Rule-Making and the Police,
70 Mich.L.Rev. 659 (1972); Amsterdam, Perspectives on the Fourth
Amendment, 58 Minn.L.Rev. 349, 416-431 (1974).

															[ Footnote 2/16 ]

															The Attorney General's Task Force on Violent Crime concluded
that the situation in which an officer relies on a duly authorized
warrant

															"is a particularly compelling example of good faith. A warrant
is a judicial mandate to an officer to conduct a search or make an
arrest, and the officer has a sworn duty to carry out its
provisions. Accordingly, we believe that there should be a rule
which states that evidence obtained pursuant to and within the
scope of a warrant is prima facie the result of good faith
on the part of the officer seizing the evidence."

															U.S. Dept. of Justice, Attorney General's Task Force on Violent
Crime, Final Report 55 (1981).

															[ Footnote 2/17 ]

															Much is made of Shadwick v. City of Tampa, 407 U.
S. 345 (1972), where we held that magistrates need not
be legally trained. Shadwick's holding was quite narrow.
First, the Court insisted that

															"an issuing magistrate must meet two tests. He must be neutral
and detached, and he must be capable of determining whether
probable cause exists for the requested arrest or search." Id. at 407 U. S. 350 .
Second, in Shadwick, the Court Clerk's authority extended
only to the relatively straightforward task of issuing arrest
warrants for breach of municipal ordinances. To issue search
warrants, an individual must be capable of making the probable
cause judgments involved. In this regard, I reject the Court's
insinuation that it is too much to expect that persons who issue
warrants remain abreast of judicial refinements of probable cause. Ante at 462 U. S. 235 .
Finally, as indicated in text, I do not propose that a warrant
clearly lacking a basis in probable cause can support a "good
faith" defense to invocation of the exclusionary rule.

															[ Footnote 2/18 ]

															Respondents and some amici contend that this practice
would be inconsistent with the Art. III requirement of an actual
case or controversy. I have no doubt that a defendant who claims
that he has been subjected to an unlawful search or seizure and
seeks suppression of the evidentiary fruits thereof raises a live
controversy within the Art. III authority of federal courts to
adjudicate. It is fully appropriate for a court to decide whether
there has been a wrong before deciding what remedy to impose. When
questions of good faith immunity have arisen under 42 U.S.C. §
1983, we have not been constrained to reach invariably the immunity
question before the violation issue. Compare O'Connor v.
Donaldson, 422 U. S. 563 (1975) (finding constitutional violation and remanding for
consideration of good faith defense), with Procunier v.
Navarette, 434 U. S. 555 , 434 U. S. 566 ,
n. 14 (1978) (finding good faith defense first). Similarly, we have
exercised discretion at times in deciding the merits of a claim
even though the error was harmless, while on other occasions
resolving the case solely by reliance on the harmless error
doctrine. Compare Milton v. Wainwright, 407 U.
S. 371 , 407 U. S. 372 (1972) (declining to decide whether admission of confession was
constitutional violation because error, if any, was harmless beyond
a reasonable doubt), with Coleman v. Alabama, 399 U. S.
1 (1970) (upholding right to counsel at preliminary
hearing and remanding for harmless error determination).

															[ Footnote 2/19 ]

															For example, a pattern or practice of official conduct that is
alleged to violate Fourth Amendment rights may be challenged by an
aggrieved individual in a suit for declaratory or injunctive
relief. See, e.g., Zurcher v. Stanford Daily, 436 U.
S. 547 (1978). (Of course, there are limits on the
circumstances in which such actions will lie. Rizzo v.
Goode, 423 U. S. 362 (1976); Los Angeles v. Lyons, 461 U. S.
95 (1983).) Although a municipality is not liable under
42 U.S.C. § 1983 on a theory of respondeat superior, local
governing bodies are subject to suit for constitutional torts
resulting from implementation of local ordinances, regulations,
policies, or even customary practices. Monell v. New York City
Dept. of Social Services, 436 U. S. 658 (1978). Such entities enjoy no immunity defense that might impede
resolution of the substantive constitutional issue. Owen v.
City of Independence, 445 U. S. 622 (1980). In addition, certain state courts may continue to suppress,
as a matter of state law, evidence in state trials for any Fourth
Amendment violation. These cases would likely provide a sufficient
supply of state criminal cases in which to resolve unsettled
questions of Fourth Amendment law. As a final alternative, I would
entertain the possibility of according the benefits of a new Fourth
Amendment rule to the party in whose case the rule is first
announced. See Stovall v. Denno, 388 U.
S. 293 , 388 U. S. 301 (1967).

															[ Footnote 2/20 ]

															The "veracity" prong is satisfied by a recitation in the
affidavit that the informant previously supplied accurate
information to the police, see McCray v. Illinois, 386 U. S. 300 , 386 U. S.
303 -304 (1967), or by proof that the informant gave his
information against his penal interest, see United States v.
Harris, 403 U. S. 573 , 403 U. S.
583 -584 (1971) (plurality opinion). The "basis of
knowledge" prong is satisfied by a statement from the informant
that he personally observed the criminal activity, or, if he came
by the information indirectly, by a satisfactory explanation of why
his sources were reliable, or, in the absence of a statement
detailing the manner in which the information was gathered, by a
description of the accused's criminal activity in sufficient detail
that the magistrate may infer that the informant is relying on
something more substantial than casual rumor or an individual's
general reputation. Spinelli v. United States, 393 U.S. at 393 U. S.
416 .

															[ Footnote 2/21 ] See United States v. Mendenhall, 446 U.
S. 544 , 446 U. S. 562 (1980) (POWELL, J., concurring in part and concurring in
judgment).

															[ Footnote 2/22 ]

															Thus, as interpreted in Spinelli, the Court in Drape r held that there was probable cause because

															"the kind of information related by the informant [was] not
generally sent ahead of a person's arrival in a city except to
those who are intimately connected with making careful arrangements
for meeting him." Spinelli, supra, at 393 U. S. 426 (WHITE, J., concurring). As I said in Spinelli, the
conclusion that Drape r itself was based on this fact is
far from inescapable. Prior to Spinelli, Draper was
susceptible to the interpretation that it stood for the proposition
that

															"the existence of the tenth and critical fact is made
sufficiently probable to justify the issuance of a warrant by
verifying nine other facts coming from the same source." Spinelli, supra, at 393 U. S.
426 -427 (WHITE, J., concurring). But it now seems clear
that the Court in Spinelli rejected this reading of Draper .

															JUSTICE BRENNAN, post at 462 U. S. 280 ,
n. 3, 462 U. S.
281 -282, erroneously interprets my Spinelli concurrence as espousing the view that "corroboration of certain
details in a tip may be sufficient to satisfy the veracity, but not
the basis of knowledge, prong of Aguilar. " Others have
made the same mistake. See, e.g., Comment, 20
Am.Crim.L.Rev. 99, 105 (1982). I did not say that corroboration
could never satisfy the "basis of knowledge" prong. My concern was,
and still is, that the prong might be deemed satisfied on the basis
of corroboration of information that does not in any way suggest
that the informant had an adequate basis of knowledge for his
report. If, however, as in Draper, the police corroborate
information from which it can be inferred that the informant's tip
was grounded on inside information, this corroboration is
sufficient to satisfy the "basis of knowledge" prong. Spinelli, 393 U.S. at 393 U. S. 426 (WHITE, J., concurring). The rules would indeed be strange if, as
JUSTICE BRENNAN suggests, post at 462 U.S. 284 , the "basis of knowledge"
prong could be satisfied by detail in the tip alone, but not by
independent police work.

															[ Footnote 2/23 ]

															JUSTICE STEVENS is correct, post at 462 U. S. 291 ,
that one of the informant's predictions proved to be inaccurate.
However, I agree with the Court, ante at 462 U. S. 245 ,
n. 14, that an informant need not be infallible.

															[ Footnote 2/24 ]

															It is also true, as JUSTICE STEVENS points out, post at 462 U. S. 292 ,
n. 3, that the fact that respondents were last seen leaving West
Palm Beach on a north-bound interstate highway is far from
conclusive proof that they were heading directly to
Bloomingdale.

															[ Footnote 2/25 ]

															I have already indicated my view, supra at 462 U. S.
263 -264, that such a "barebones" affidavit could not be
the basis for a good faith issuance of a warrant.

															[ Footnote 2/26 ] Bridger v. State, 503
S.W.2d 801 (Tex.Crim.App.1974), and People v. Palanza, 55 Ill.App.3d 1028, 371 N.E.2d 687 (1978), which the Court
describes ante at 462 U. S. 234 , n. 9, appear to me to be excellent
examples of overly technical applications of the Aguilar-Spinelli standard. The holdings in these cases
could easily be disapproved without reliance on a "totality of the
circumstances" analysis.

															JUSTICE BRENNAN, with whom JUSTICE MARSHALL joins,
dissenting.

															Although I join JUSTICE STEVENS' dissenting opinion and agree
with him that the warrant is invalid even under the Court's newly
announced "totality of the circumstances" test, see post at 462 U. S.
294 -295, and n. 8, I write separately to dissent from
the Court's unjustified and ill-advised rejection of the two-prong
test for evaluating the validity of a warrant based on hearsay
announced in Aguilar v. Texas, 378 U.
S. 108 (1964), and refined in Spinelli v. United
States, 393 U. S. 410 (1969). I The Court's current Fourth Amendment jurisprudence, as reflected
by today's unfortunate decision, patently disregards Justice
Jackson's admonition in Brinegar v. United States, 338 U. S. 160 (1949):

															"[Fourth Amendment rights] are not mere second-class rights, but
belong in the catalog of indispensable freedoms. Among deprivations
of rights, none is so effective in cowing a population, crushing
the spirit of the individual and putting terror in every heart. Page 462 U. S. 275 Uncontrolled search and seizure is one of the first and most
effective weapons in the arsenal of every arbitrary government. . .
."

															"But the right to be secure against searches and seizures is one
of the most difficult to protect. Since the officers are themselves
the chief invaders, there is no enforcement outside of court." Id. at 338 U. S.
180 -181 (dissenting opinion).

															In recognition of the judiciary's role as the only effective
guardian of Fourth Amendment rights, this Court has developed over
the last half century a set of coherent rules governing a
magistrate's consideration of a warrant application and the
showings that are necessary to support a finding of probable cause.
We start with the proposition that a neutral and detached
magistrate, and not the police, should determine whether there is
probable cause to support the issuance of a warrant. In Johnson
v. United States, 333 U. S. 10 (1948), the Court stated:

															"The point of the Fourth Amendment, which often is not grasped
by zealous officers, is not that it denies law enforcement the
support of the usual inferences which reasonable men draw from
evidence. Its protection consists in requiring that those
inferences be drawn by a neutral and detached magistrate, instead
of being judged by the officer engaged in the often competitive
enterprise of ferreting out crime. . . . When the right of privacy
must reasonably yield to the right of search is, as a rule, to be
decided by a judicial officer, not by a policeman or government
enforcement agent." Id. at 333 U. S. 13 -14
(footnote omitted). See also Whiteley v. Warden, 401 U. S. 560 , 401 U. S. 564 (1971); Spinelli v. United States, supra, at 393 U. S. 415 ; United States v. Ventresca, 380 U.
S. 102 , 380 U. S. 109 (1965); Aguilar v. Texas, supra, at 378 U. S. 111 ; Jones v. United States, 362 U. S. 257 , 362 U. S.
270 -271 Page 462 U. S. 276 (1960); Giordenello v. United States, 357 U.
S. 480 , 357 U. S. 486 (1968); United States v. Lefkowitz, 285 U.
S. 452 , 285 U. S. 464 (1932).

															In order to emphasize the magistrate's role as an independent
arbiter of probable cause and to insure that searches or seizures
are not effected on less than probable cause, the Court has
insisted that police officers provide magistrates with the
underlying facts and circumstances that support the officers'
conclusions. In Nathanson v. United States, 290 U. S.
41 (1933), the Court held invalid a search warrant that
was based on a customs agent's "mere affirmation of suspicion and
belief without any statement of adequate supporting facts." Id. at 290 U. S. 46 .
The Court stated:

															"Under the Fourth Amendment, an officer may not properly issue a
warrant to search a private dwelling unless he can find probable
cause therefor from facts or circumstances presented to him under
oath or affirmation. Mere affirmance of belief or suspicion is not
enough." Id. at 290 U. S. 47 .

															In Giordenello v. United States, supra, the Court
reviewed an arrest warrant issued under the Federal Rules of
Criminal Procedure based on a complaint sworn to by a Federal
Bureau of Narcotics agent. Id. at 357 U. S. 481 .
[ Footnote 3/1 ] Based on the agent's
testimony at the suppression hearing, the Court noted that,

															"until the warrant was issued . . . , [the agent's] suspicions
of petitioner's guilt derived entirely from information given him
by law enforcement officers and other persons in Houston, none of
whom either appeared before the Commissioner or submitted
affidavits." Id. at 357 U. S. 485 .
The Court found it unnecessary to decide whether a warrant could be
based solely on hearsay information, for the complaint was
"defective in not providing a sufficient basis upon which a Page 462 U. S. 277 finding of probable cause could be made." Ibid. In
particular, the complaint contained no affirmative allegation that
the agent spoke with personal knowledge, nor did it indicate any
sources for the agent's conclusion. Id. at 357 U. S. 486 .
The Court expressly rejected the argument that these deficiencies
could be cured by "the Commissioner's reliance upon a presumption
that the complaint was made on the personal knowledge of the
complaining officer." Ibid. As noted, the Court did not decide the hearsay question lurking
in Giordenello. The use of hearsay to support the issuance
of a warrant presents special problems, because informants, unlike
police officers, are not regarded as presumptively reliable or
honest. Moreover, the basis for an informant's conclusions is not
always clear from an affidavit that merely reports those
conclusions. If the conclusory allegations of a police officer are
insufficient to support a finding of probable cause, surely the
conclusory allegations of an informant should a fortiori be insufficient.

															In Jones v. United States, supra, the Court
considered

															"whether an affidavit which sets out personal observations
relating to the existence of cause to search is to be deemed
insufficient by virtue of the fact that it sets out not the
affiant's observations but those of another." Id. at 362 U. S. 269 .
The Court held that hearsay information can support the issuance of
a warrant "so long as a substantial basis for crediting the hearsay
is presented." Ibid. The Court found that there was a
substantial basis for crediting the hearsay involved in Jones. The informant's report was based on the informant's
personal knowledge, and the informant previously had provided
accurate information. Moreover, the informant's story was
corroborated by other sources. Finally, the defendant was known to
the police to be a narcotics user. Id. at 362 U. S.
271 . Aguilar v. Texas, 378 U. S. 108 (1964), merely made explicit what was implicit in Jones. In considering a search warrant based on hearsay, the Court
reviewed Nathanson Page 462 U. S. 278 and Giordenello and noted the requirement established
by those cases that an officer provide the magistrate with the
underlying facts or circumstances that support the officer's
conclusion that there is probable cause to justify the issuance of
a warrant. The Court stated:

															"The vice in the present affidavit is at least as great as in Nathanson and Giordenello. Here, the 'mere
conclusion' that petitioner possessed narcotics was not even that
of the affiant himself; it was that of an unidentified informant.
The affidavit here not only 'contains no affirmative allegation
that the affiant spoke with personal knowledge of the matters
contained therein,' it does not even contain an 'affirmative
allegation' that the affiant's unidentified source 'spoke with
personal knowledge.' For all that appears, the source here merely
suspected, believed or concluded that there were narcotics in
petitioner's possession. The magistrate here certainly could not
'judge for himself the persuasiveness of the facts relied on . . .
to show probable cause.' He necessarily accepted 'without question'
the informant's 'suspicion,' 'belief' or 'mere conclusion.'"

															378 U.S. at 378 U. S.
113 -114 (footnote omitted). [ Footnote 3/2 ]

															While recognizing that a warrant may be based on hearsay, the
Court established the following standard:

															"[T]he magistrate must be informed of some of the underlying
circumstances from which the informant concluded Page 462 U. S. 279 that the narcotics were where he claimed they were, and some of
the underlying circumstances from which the officer concluded that
the informant, whose identity need not be disclosed . . . was
'credible' or his information 'reliable.' Otherwise, 'the
inferences from the facts which lead to the complaint' will be
drawn not 'by a neutral and detached magistrate,' as the
Constitution requires, but instead, by a police officer 'engaged in
the often competitive enterprise of ferreting out crime' . . . or,
as in this case, by an unidentified informant." Id. at 378 U. S.
114 -115 (footnote omitted).

															The Aguilar standard was refined in Spinelli v.
United States, 393 U. S. 410 (1969). In Spinelli, the Court reviewed a search warrant
based on an affidavit that was "more ample," id. at 393 U. S. 413 ,
than the one in Aguilar. The affidavit in Spinelli contained not only a tip from an informant, but
also a report of an independent police investigation that allegedly
corroborated the informant's tip. 393 U.S. at 393 U. S. 413 .
Under these circumstances, the Court stated that it was "required
to delineate the manner in which Aguilar's two-pronged
test should be applied. . . ." Ibid. The Court held that the Aguilar test should be applied
to the tip, and approved two additional ways of satisfying that
test. First, the Court suggested that, if the tip contained
sufficient detail describing the accused's criminal activity, it
might satisfy Aguilar's basis of knowledge prong. 393 U.S.
at 393 U. S. 416 .
Such detail might assure the magistrate that he is

															"relying on something more substantial than a casual rumor
circulating in the underworld or an accusation based merely on an
individual's general reputation." Ibid. Although the tip in the case before it did not
meet this standard, "[t]he detail provided by the informant in Draper v. United States, 358 U. S. 307 (1959), provide[d] a suitable benchmark," ibid., because
"[a] magistrate, when confronted with such detail, could reasonably
infer that the informant Page 462 U. S. 280 had gained his information in a reliable way." Id. at 393 U. S. 417 (footnote omitted). [ Footnote
3/3 ]

															Second, the Court stated that police corroboration of the
details of a tip could provide a basis for satisfying Aguilar. Page 462 U. S. 281 393 U.S. at 393 U. S. 417 .
The Court's opinion is not a model of clarity on this issue, since
it appears to suggest that corroboration can satisfy both the basis
of knowledge and veracity prongs of Aguilar. 393 U.S. at 393 U. S.
417 -418. [ Footnote 3/4 ]
JUSTICE WHITE's concurring opinion, however, points the way to a
proper reading of the Court's opinion. After reviewing the Court's
decision in Draper v. United States, 358 U.
S. 307 (1959), JUSTICE WHITE concluded that "[t]he
thrust of Draper is not that the verified facts have
independent significance with respect to proof of [another
unverified fact]." 393 U.S. at 393 U. S. 427 .
In his view,

															"[t]he argument instead relates to the reliability of the
source: because an informant is right about some things, he is more
probably right about other facts, usually the critical, unverified
facts." Ibid. JUSTICE WHITE then pointed out that prior cases
had rejected "the notion that the past Page 462 U. S. 282 reliability of an officer is sufficient reason for believing his
current assertions." Ibid. JUSTICE WHITE went on to
state:

															"Nor would it suffice, I suppose, if a reliable informant states
there is gambling equipment in Apartment 607 and then proceeds to
describe in detail Apartment 201, a description which is verified
before applying for the warrant. He was right about 201, but that
hardly makes him more believable about the equipment in 607. But
what if he states that there are narcotics locked in a safe in
Apartment 300, which is described in detail, and the apartment
manager verifies everything but the contents of the safe? I doubt
that the report about the narcotics is made appreciably more
believable by the verification. The informant could still have
gotten his information concerning the safe from others about whom
nothing is known or could have inferred the presence of narcotics
from circumstances which a magistrate would find unacceptable." Ibid. I find this reasoning persuasive. Properly understood,
therefore, Spinelli stands for the proposition that
corroboration of certain details in a tip may be sufficient to
satisfy the veracity, but not the basis of knowledge, prong of Aguilar. As noted, Spinelli also suggests that,
in some limited circumstances, considerable detail in an
informant's tip may be adequate to satisfy the basis of knowledge
prong of Aguilar. [ Footnote
3/5 ] Page 462 U. S. 283 Although the rules drawn from the cases discussed above are cast
in procedural terms, they advance an important underlying
substantive value: findings of probable cause, and attendant
intrusions, should not be authorized unless there is some assurance
that the information on which they are based has been obtained in a
reliable way by an honest or credible person. As applied to police
officers, the rules focus on the way in which the information was
acquired. As applied to informants, the rules focus both on the
honesty or credibility of the informant and on the reliability of
the way in which the information was acquired. Insofar as it is
more complicated, an evaluation of affidavits based on hearsay
involves a more difficult inquiry. This suggests a need to
structure the inquiry in an effort to insure greater accuracy. The
standards announced in Aguilar, as refined by Spinelli, fulfill that need. The standards inform the
police of what information they have to provide and magistrates of
what information they should demand. The standards also inform
magistrates of the subsidiary findings they must make in order to
arrive at an ultimate finding of probable cause. Spinelli, properly understood, directs the magistrate's attention to the
possibility that the presence of self-verifying detail might
satisfy Aguilar's basis of knowledge prong, and that
corroboration of the details of a tip might satisfy Aguilar's veracity prong. By requiring police to provide
certain crucial information to magistrates and by structuring
magistrates' probable cause inquiries, Aguilar and Spinelli assure the magistrate's role as an independent
arbiter of probable cause, insure greater accuracy in probable
cause determinations, and advance the substantive value identified
above.

															Until today, the Court has never squarely addressed the
application of the Aguilar and Spinelli standards
to tips from anonymous informants. Both Aguilar and Spinelli dealt with tips from informants known at least to
the police. See also e.g., Adams v. Williams, 407 U.
S. 143 , 407 U. S. 146 (1972); United States v. Harris, 403 U.
S. 573 , 403 U. S. 575 (1971); Whiteley v. Warden, 401 U.S. at 565; McCray v.
Illinois , 386 U.S. Page 462 U. S. 284 300, 386 U. S. 302 (1967); Jones v. United States, 362 U.S. at 362 U. S.
268 -269. And surely there is even more reason to subject
anonymous informants' tips to the tests established by Aguilar and Spinelli. By definition, nothing is
known about an anonymous informant's identity, honesty, or
reliability. One commentator has suggested that anonymous
informants should be treated as presumptively unreliable. See Comment, Anonymous Tips, Corroboration, and Probable
Cause: Reconciling the Spinelli/Draper Dichotomy in Illinois v. Gates, 20 Am.Crim.L.Rev. 99, 107 (1982). See also Adams v. Williams, supra, at 407 U. S. 146 (suggesting that an anonymous telephone tip provides a weaker case
for a Terry v. Ohio, 392 U. S. 1 (1968),
stop than a tip from an informant known to the police who had
provided information in the past); United States v. Harris,
supra, at 403 U. S. 599 (Harlan, J., dissenting) ("We cannot assume that the ordinary
law-abiding citizen has qualms about [appearing before a
magistrate]"). In any event, there certainly is no basis for
treating anonymous informants as presumptively reliable. Nor is
there any basis for assuming that the information provided by an
anonymous informant has been obtained in a reliable way. If we are
unwilling to accept conclusory allegations from the police, who are
presumptively reliable, or from informants who are known, at least
to the police, there cannot possibly be any rational basis for
accepting conclusory allegations from anonymous informants.

															To suggest that anonymous informants' tips are subject to the
tests established by Aguilar and Spinelli is not
to suggest that they can never provide a basis for a finding of
probable cause. It is conceivable that police corroboration of the
details of the tip might establish the reliability of the informant
under Aguilar's veracity prong, as refined in Spinelli, and that the details in the tip might be
sufficient to qualify under the "self-verifying detail" test
established by Spinelli as a means of satisfying Aguilar's basis of knowledge prong. The Aguilar and Spinelli tests must be applied to anonymous
informants' tips, however, if we are to continue to insure Page 462 U. S. 285 that findings of probable cause, and attendant intrusions, are
based on information provided by an honest or credible person who
has acquired the information in a reliable way. [ Footnote 3/6 ]

															In light of the important purposes served by Aguilar and Spinelli, I would not reject the standards they
establish. If anything, I simply would make more clear that Spinelli, properly understood, does not depart in any
fundamental way from the test established by Aguilar. For
reasons I shall next state, I do not find persuasive the Court's
justifications for rejecting the test established by Aguilar and refined by Spinelli. Page 462 U. S. 286 II In rejecting the Aguilar-Spinelli standards, the Court
suggests that a

															"totality-of-the-circumstances approach is far more consistent
with our prior treatment of probable cause than is any rigid demand
that specific 'tests' be satisfied by every informant's tip." Ante at 462 U. S.
230 -231 (footnote omitted). In support of this
proposition, the Court relies on several cases that purportedly
reflect this approach, ante at 462 U. S.
230 -231, n. 6, 462 U. S.
232 -233, n. 7, and on the "practical, nontechnical," ante at 462 U. S. 231 ,
nature of probable cause.

															Only one of the cases cited by the Court in support of its
"totality of the circumstances" approach, Jaben v. United
States, 381 U. S. 214 (1965), was decided subsequent to Aguilar. It is by no
means inconsistent with Aguilar. [ Footnote 3/7 ] The other three cases [ Footnote 3/8 ] cited by the Court as supporting
its Page 462 U. S. 287 totality-of-the-circumstances approach were decided before Aguilar. In any event, it is apparent from the Court's
discussion of them, see ante at 462 U. S.
232 -233, n. 7, that they are not inconsistent with Aguilar. In addition, one can concede that probable cause is a
"practical, nontechnical" concept without betraying the values that Aguilar and Spinelli reflect. As noted, see
supra at 462 U. S.
277 -282, Aguilar and Spinelli require
the police to provide magistrates with certain crucial information.
They also provide structure for magistrates' probable cause
inquiries. In so doing, Aguilar and Spinelli preserve the role of magistrates as independent arbiters of
probable cause, insure greater accuracy in probable cause
determinations, and advance the substantive value of precluding
findings of probable cause, and attendant intrusions, based on
anything less than information from an honest or credible person
who has acquired his information in a reliable way. Neither the
standards nor their effects are inconsistent with a "practical,
nontechnical" conception of probable cause. Once a magistrate has
determined that he has information before him that he can
reasonably say has been obtained in a reliable way by a credible
person, he has ample room to use his common sense and to apply a
practical, nontechnical conception of probable cause.

															It also should be emphasized that cases such as Nathanson v.
United States, 290 U. S. 41 (1933), and Giordenello v. United States, 357 U.
S. 480 (1958), discussed supra, at 462 U. S.
276 -277, directly contradict the Court's suggestion, ante at 462 U. S. 233 ,
that a strong showing on one prong of the Aguilar test
should compensate for a deficient showing on the other. If the
conclusory allegations of a presumptively reliable police officer
are insufficient to establish probable cause, there is no
conceivable reason why the conclusory allegations of an anonymous
informant should not be insufficient as well. Moreover, contrary to
the Court's implicit suggestion, Aguilar and Spinelli do not stand as an insuperable barrier to the
use Page 462 U. S. 288 of even anonymous informants' tips to establish probable cause. See supra at 462 U. S.
277 -282. It is no justification for rejecting them
outright that some courts may have employed an overly technical
version of the Aguilar-Spinelli standards, see
ante at 462 U. S.
234 -235, and n. 9.

															The Court also insists that the Aguilar-Spinelli standards must be abandoned because they are inconsistent with the
fact that nonlawyers frequently serve as magistrates. Ante at 462 U. S.
235 -236. To the contrary, the standards help to
structure probable cause inquiries and, properly interpreted, may
actually help a nonlawyer magistrate in making a probable cause
determination. Moreover, the Aguilar and Spinelli tests are not inconsistent with deference to magistrates'
determinations of probable cause. Aguilar expressly
acknowledged that reviewing courts "will pay substantial deference
to judicial determinations of probable cause. . . ." 378 U.S. at 378 U. S. 111 .
In Spinelli, the Court noted that it was not retreating
from the proposition that magistrates' determinations of probable
cause "should be paid great deference by reviewing courts. . . ."
393 U.S. at 393 U. S. 419 .
It is also noteworthy that the language from United States v.
Ventresca, 380 U.S. at 380 U. S.
108 -109, which the Court repeatedly quotes, see
ante at 462 U. S. 235 , 462 U. S. 236 ,
and 462 U. S. 237 ,
n. 10, brackets the following passage, which the Court does not
quote:

															"This is not to say that probable cause can be made out by
affidavits which are purely conclusory, stating only the affiant's
or an informer's belief that probable cause exists without
detailing any of the 'underlying circumstances' upon which that
belief is based. See Aguilar v. Texas, supra. Recital of
some of the underlying circumstances in the affidavit is essential
if the magistrate is to perform his detached function and not serve
merely as a rubber stamp for the police. However, where these
circumstances are detailed, where reason for crediting the source
of the information is given, and when a magistrate has found
probable cause, the courts should not Page 462 U. S. 289 invalidate the warrant by interpreting the affidavit in a
hypertechnical, rather than a common sense, manner."

															380 U.S. at 380 U. S.
108 -109. [ Footnote
3/9 ]

															At the heart of the Court's decision to abandon Aguilar and Spinelli appears to be its belief that

															"the direction taken by decisions following Spinelli poorly serves '[t]he most basic function of any government:' 'to
provide for the security of the individual and of his
property.'" Ante at 462 U. S. 237 .
This conclusion rests on the judgment that Aguilar and Spinelli "seriously imped[e] the task of law enforcement," ante at 462 U. S. 237 ,
and render anonymous tips valueless in police work. Ibid. Surely, the Court overstates its case. See supra at 462 U. S.
287 -288. But of particular concern to all Americans must
be that the Court gives virtually no consideration to the value of
insuring that findings of probable cause are based on information
that a magistrate can reasonably say has been obtained in a
reliable Page 462 U. S. 290 way by an honest or credible person. I share JUSTICE WHITE's
fear that the Court's rejection of Aguilar and Spinelli and its adoption of a new
totality-of-the-circumstances test, ante at 462 U. S. 238 ,
"may foretell an evisceration of the probable cause standard. . .
." Ante at 462 U. S. 272 (WHITE, J., concurring in judgment). III The Court's complete failure to provide any persuasive reason
for rejecting Aguilar and Spinelli doubtlessly
reflects impatience with what it perceives to be "overly technical"
rules governing searches and seizures under the Fourth Amendment.
Words such as "practical," "nontechnical," and "common sense," as
used in the Court's opinion, are but code words for an overly
permissive attitude towards police practices in derogation of the
rights secured by the Fourth Amendment. Everyone shares the Court's
concern over the horrors of drug trafficking, but under our
Constitution, only measures consistent with the Fourth Amendment
may be employed by government to cure this evil. We must be ever
mindful of Justice Stewart's admonition in Coolidge v. New
Hampshire, 403 U. S. 443 (1971):

															"In times of unrest, whether caused by crime or racial conflict
or fear of internal subversion, this basic law and the values that
it represents may appear unrealistic or 'extravagant' to some. But
the values were those of the authors of our fundamental
constitutional concepts." Id. at 403 U. S. 455 (plurality opinion). In the same vein, Glasser v. United
States, 315 U. S. 60 (1942), warned that "[s]teps innocently taken may, one by one, lead
to the irretrievable impairment of substantial liberties." Id. at 315 U. S.
86 .

															Rights secured by the Fourth Amendment are particularly
difficult to protect, because their "advocates are usually
criminals." Draper v. United States, 358 U.S. at 358 U. S. 314 (Douglas, J., dissenting). But the rules "we fashion [are] for the
innocent and guilty alike." Ibid. See also Kolender v.
Lawson, 461 U. S. 352 , 461 U. S. 362 ,
n. 1 (1983) (BRENNAN, J., concurring); Brinegar v. United
States, 338 U.S. at 338 U. S. 181 (Jackson, J., dissenting). Page 462 U. S. 291 By replacing Aguilar and Spinelli with a test
that provides no assurance that magistrates, rather than the
police, or informants, will make determinations of probable cause;
imposes no structure on magistrates' probable cause inquiries; and
invites the possibility that intrusions may be justified on less
than reliable information from an honest or credible person,
today's decision threatens to

															"obliterate one of the most fundamental distinctions between our
form of government, where officers are under the law, and the
police state, where they are the law." Johnson v. United States, 333 U.S. at 333 U. S.
17 .

															[ Footnote 3/1 ]

															Although the warrant was issued under the Federal Rules of
Criminal Procedure, the Court stated that "[t]he provisions of
these Rules must be read in light of the constitutional
requirements they implement." 357 U.S. at 357 U. S. 485 . See Aguilar v. Texas, 378 U. S. 108 , 378 U. S. 112 ,
n. 3 (1964) ("The principles announced in Giordenello derived . . . from the Fourth Amendment, and not from our
supervisory power").

															[ Footnote 3/2 ]

															The Court noted that approval of the affidavit before it "would
open the door to easy circumvention of the rule announced in Nathanson and Giordenello. " 378 U.S. at 378 U. S. 114 ,
n. 4. The Court stated:

															"A police officer who arrived at the 'suspicion,' 'belief' or
'mere conclusion' that narcotics were in someone's possession could
not obtain a warrant. But he could convey this conclusion to
another police officer, who could then secure the warrant by
swearing that he had 'received reliable information from a credible
person' that the narcotics were in someone's possession." Ibid. [ Footnote 3/3 ]

															There is some tension between Draper v. United States, 358 U. S. 307 (1959), and Aguilar. In Draper, the Court
considered the validity of a warrantless arrest based on an
informant's tip and police corroboration of certain details of the
tip. The informant, who in the past had always given accurate and
reliable information, told the police that Draper was peddling
narcotics. The informant later told the police that Draper had left
for Chicago by train to pick up some heroin and would return by
train on the morning of one of two days. The informant gave the
police a detailed physical description of Draper and of the
clothing he was wearing. The informant also said that Draper would
be carrying a tan zipper bag and that he walked very fast. 358 U.S.
at 358 U. S.
309 .

															On the second morning specified by the informant, the police saw
a man

															"having the exact physical attributes and wearing the precise
clothing described by [the informant], alight from an incoming
Chicago train and start walking 'fast' toward the exit." Id. at 358 U. S.
309 -310. The man was carrying a tan zipper bag. The
police arrested him and searched him incident to the arrest. Id. at 358 U. S.
310 .

															The Court found that the arrest had been based on probable
cause. Having verified every detail of the tip "except whether
[Draper] had accomplished his mission and had the three ounces of
heroin on his person or in his bag," id. at 358 U. S. 313 ,
the police "had reasonable grounds' to believe that the
remaining unverified bit of [the informant's] information . . . was
likewise true." Ibid. There is no doubt that the tip satisfied Aguilar's veracity prong. The informant had given accurate information in the
past. Moreover, under Spinelli, the police corroborated
most of the details of the informant's tip. See Spinelli v.
United States, 393 U.S. at 393 U. S. 417 ; id. at 393 U. S.
426 -427 (WHITE, J., concurring); infra at 462 U. S. 281 ,
and n. 4. There is some question, however, about whether the tip
satisfied Aguilar's basis of knowledge prong. The fact
that an informant is right about most things may suggest that he is
credible, but it does not establish that he has acquired his
information in a reliable way. See Spinelli v. United States,
supra, at 393 U. S.
426 -427 (WHITE, J., concurring). Spinelli's "self-verifying detail" element resolves this tension. As one
commentator has suggested, "under Spinelli, the Draper decision is sound as applied to its facts." Note,
The Informer's Tip As Probable Cause for Search or Arrest, 54
Cornell L.Rev. 958, 964, n. 34 (1969).

															[ Footnote 3/4 ]

															The Court stated that the Federal Bureau of Investigation's
independent investigative efforts could not

															"support both the inference that the informer was generally
trustworthy and that he had made his charge against Spinelli on the basis of information obtained in a
reliable way." Spinelli v. United States, supra, at 393 U. S. 417 .
The Court suggested that Draper again provided "a relevant
comparison." 393 U.S. at 393 U. S. 417 .
Once the police had corroborated most of the details of the tip in Draper, "[i]t was . . . apparent that the informant had not been
fabricating his report out of whole cloth; since the report was of
the sort which, in common experience, may be recognized as having
been obtained in a reliable way, it was perfectly clear that
probable cause had been established."

															393 U.S. at 393 U. S.
417 -418.

															It is the Court's citation of Draper which creates most
of the confusion. The informant's credibility was not at issue in Draper irrespective of the corroboration of the details of
his tip. See 462
U.S. 213 fn2/3|>n. 3, supra. The Court's opinion,
therefore, might be read as suggesting that corroboration also
could satisfy Aguilar's basis of knowledge test. I think
it is more likely, however, especially in view of the discussion infra, this page and 462 U. S. 282 ,
that the Court simply was discussing an alternative means of
satisfying Aguilar's veracity prong, using the facts of Draper as an example, and relying on its earlier
determination that the detail of the tip in Draper was
self-verifying. See 393 U.S. at 393 U. S.
416 -417. It is noteworthy that, although the affiant in Spinelli had sworn that the informer was reliable, "he
[had] offered the magistrate no reason in support of this
conclusion." Id. at 393 U. S. 416 . Aguilar's veracity prong, therefore, was not satisfied.
393 U.S. at 393 U. S.
416 .

															[ Footnote 3/5 ]

															After concluding that the tip was not sufficient to support a
finding of probable cause, the Court stated:

															"This is not to say that the tip was so insubstantial that it
could not properly have counted in the magistrate's determination.
Rather, it needed some further support. When we look to the other
parts of the application, however, we find nothing alleged which
would permit the suspicions engendered by the informant's report to
ripen into a judgment that a crime was probably being
committed." Spinelli v. United States, 393 U.S. at 393 U. S. 418 .
The Court went on to suggest that corroboration of incriminating
facts would be needed. See ibid. [ Footnote 3/6 ]

															As noted supra at 462 U. S.
277 -282, Aguilar and Spinelli inform
the police of what information they have to provide and magistrates
of what information they should demand. This advances the important
process value, which is intimately related to substantive Fourth
Amendment concerns, of having magistrates, rather than police or
informants, determine whether there is probable cause to support
the issuance of a warrant. We want the police to provide
magistrates with the information on which they base their
conclusions so that magistrates can perform their important
function. When the police rely on facts about which they have
personal knowledge, requiring them to disclose those facts to
magistrates imposes no significant burden on the police. When the
police rely on information obtained from confidential informants,
requiring the police to disclose the facts on which the informants
based their conclusions imposes a more substantial burden on the
police, but it is one that they can meet because they presumably
have access to their confidential informants.

															In cases in which the police rely on information obtained from
an anonymous informant, the police, by hypothesis, cannot obtain
further information from the informant regarding the facts and
circumstances on which the informant based his conclusion. When the
police seek a warrant based solely on an anonymous informant's tip,
therefore, they are providing the magistrate with all the
information on which they have based their conclusion. In this
respect, the command of Aguilar and Spinelli has
been met and the process value identified above has been served.
But Aguilar and Spinelli advance other values
which argue for their application even to anonymous informants'
tips. They structure the magistrate's probable cause inquiry and,
more importantly, they guard against findings of probable cause,
and attendant intrusions, based on anything other than information
which magistrates reasonably can conclude has been obtained in a
reliable way by an honest or credible person.

															[ Footnote 3/7 ]

															In Jaben v. United States, the Court considered whether
there was probable cause to support a complaint charging petitioner
with willfully filing a false tax return. 381 U.S. at 381 U. S. 221 .
After reviewing the extensive detail contained in the complaint, id. at 381 U. S. 223 ,
the Court expressly distinguished tax offenses from other types of
offenses:

															"Some offenses are subject to putative establishment by blunt
and concise factual allegations, e.g., 'A saw narcotics in
B's possession,' whereas 'A saw B file a false tax return' does not
mean very much in a tax evasion case. Establishment of grounds for
belief that the offense of tax evasion has been committed often
requires a reconstruction of the taxpayer's income from many
individually unrevealing facts which are not susceptible of a
concise statement in a complaint. Furthermore, unlike narcotics
informants, for example, whose credibility may often be suspect,
the sources in this tax evasion case are much less likely to
produce false or untrustworthy information. Thus, whereas some
supporting information concerning the credibility of informants in
narcotics cases or other common garden varieties of crime may be
required, such information is not so necessary in the context of
the case before us." Id. at 381 U. S.
223 -224. Obviously, Jaben is not inconsistent
with Aguilar, and involved no general rejection of the Aguilar standards.

															[ Footnote 3/8 ] Rugendorf v. United States, 376 U.
S. 528 (1964); Ker v. California, 374 U. S.
23 (1963); Jones v. United States, 362 U.
S. 257 (1960).

															[ Footnote 3/9 ]

															The Court also argues that,

															"[i]f the affidavits submitted by police officers are subjected
to the type of scrutiny some courts have deemed appropriate, police
might well resort to warrantless searches, with the hope of relying
on consent or some other exception to the Warrant Clause that might
develop at the time of the search." Ante at 462 U. S. 236 .
If the Court is suggesting, as it appears to be, that the police
will intentionally disregard the law, it need only be noted in
response that the courts are not helpless to deal with such
conduct. Moreover, as was noted in Coolidge v. New
Hampshire, 403 U. S. 443 (1971):

															"[T]he most basic constitutional rule in this area is that"

															"searches conducted outside the judicial process, without prior
approval by judge or magistrate, are per se unreasonable
under the Fourth Amendment -- subject only to a few specifically
established and well-delineted exceptions."

															"The exceptions are 'jealously and carefully drawn,' and there
must be 'a showing by those who seek exemption . . . that the
exigencies of the situation made that course imperative.' '[T]he
burden is on those seeking the exemption to show the need for
it.'" Id. at 403 U. S.
454 -455 (plurality opinion) (footnotes omitted). It
therefore would appear to be not only inadvisable, but also
unavailing, for the police to conduct warrantless searches in "the
hope of relying on consent or some other exception to the Warrant
Clause that might develop at the time of the search." Ante at 462 U. S.
236 .

															JUSTICE STEVENS, with whom JUSTICE BRENNAN joins,
dissenting.

															The fact that Lance and Sue Gates made a 22-hour nonstop drive
from West Palm Beach, Florida, to Bloomingdale, Illinois, only a
few hours after Lance had flown to Florida provided persuasive
evidence that they were engaged in illicit activity. That fact,
however, was not known to the judge when he issued the warrant to
search their home.

															What the judge did know at that time was that the anonymous
informant had not been completely accurate in his or her
predictions. The informant had indicated that " sue . . . drives
their car to Florida where she leaves it to be loaded up with
drugs. . . . Sue fl[ies] back after she drops the car off in
Florida. '" 85 Ill. 2d
376 , 379, 423 N.E.2d
887 , 888 (1981) (emphasis added). Yet Detective Mader's
affidavit reported that she "`left the West Palm Beach area driving
the Mercury north-bound.'" 82 Ill.App.3d 749, 757, 403 N.E.2d 77,
82 (1980). The discrepancy between the informant's predictions and the
facts known to Detective Mader is significant for three reasons.
First, it cast doubt on the informant's hypothesis that the Gates
already had " over [$100,000] worth of drugs in their
basement,'" 85 Ill. 2d at 379, 423 N.E.2d at 888. The informant had
predicted an itinerary that always kept one Page 462 U. S.
292 spouse in Bloomingdale, suggesting that the Gates did not
want to leave their home unguarded because something valuable was
hidden within. That inference obviously could not be drawn when it
was known that the pair was actually together over a thousand miles
from home. Second, the discrepancy made the Gates' conduct seem
substantially less unusual than the informant had predicted it
would be. It would have been odd if, as predicted, Sue had driven
down to Florida on Wednesday, left the car, and flown right back to
Illinois. But the mere facts that Sue was in West Palm Beach with
the car, [ Footnote 4/1 ] that she
was joined by her husband at the Holiday Inn on Friday, [ Footnote 4/2 ] and that the couple drove
north together the next morning [ Footnote 4/3 ] are neither unusual nor probative of
criminal activity. Page 462 U. S. 293 Third, the fact that the anonymous letter contained a material
mistake undermines the reasonableness of relying on it as a basis
for making a forcible entry into a private home. [ Footnote 4/4 ]

															Of course, the activities in this case did not stop when the
judge issued the warrant. The Gates drove all night to
Bloomingdale, the officers searched the car and found 400 pounds of
marihuana, and then they searched the house. [ Footnote 4/5 ] However, none of these subsequent events
may be considered in evaluating the warrant, [ Footnote 4/6 ] and the search of the house was legal only
if the warrant was valid. Vale v. Louisiana, 399 U. S.
30 , 399 U. S. 33 -35
(1970). I cannot accept the Court's casual conclusion that, before the Gates arrived in Bloomindale, there was
probable cause to justify a valid entry and search of a private
home. No one knows who the informant in this case was, or what
motivated him or her to write the note. Given that the note's
predictions were faulty in one Page 462 U. S. 294 significant respect, and were corroborated by nothing except
ordinary innocent activity, I must surmise that the Court's
evaluation of the warrant's validity has been colored by subsequent
events. [ Footnote 4/7 ]

															Although the foregoing analysis is determinative as to the house
search, the car search raises additional issues, because "there is
a constitutional difference between houses and cars." Chambers
v. Maroney, 399 U. S. 42 , 399 U. S. 52 (1970). Cf. Payton v. New York, 445 U.
S. 573 , 445 U. S.
589 -590 (1980). An officer who has probable cause to
suspect that a highly movable automobile contains contraband does
not need a valid warrant in order to search it. This point was
developed in our opinion in United States v. Ross, 456 U. S. 798 (1982), which was not decided until after the Illinois Supreme
Court rendered its decision in this case. Under Ross, the
car search may have been valid if the officers had probable cause after the Gates arrived.

															In apologizing for its belated realization that we should not
have ordered reargument in this case, the Court today shows high
regard for the appropriate relationship of this Court to state
courts. Ante at 462 U. S.
221 -222. When the Court discusses the merits, however,
it attaches no weight to the conclusions of the Circuit Judge of Du
Page County, Illinois, of the three judges of the Second District
of the Illinois Appellate Court, or of the five justices of the
Illinois Supreme Court, all of whom concluded that the warrant was
not based on probable cause. In a fact-bound inquiry of this sort,
the judgment of three levels of state courts, all of which are
better able to evaluate the probable reliability of anonymous
informants in Page 462 U. S. 295 Bloomingdale, Illinois, than we are, should be entitled to at
least a presumption of accuracy. [ Footnote 4/8 ] I would simply vacate the judgment of the
Illinois Supreme Court and remand the case for reconsideration in
the light of our intervening decision in United States v.
Ross. [ Footnote 4/1 ]

															The anonymous note suggested that she was going down on
Wednesday, 85 Ill. 2d at 379, 423 N.E.2d at 888, but for all the
officers knew, she had been in Florida for a month. 82 Ill.App.3d
at 755-757, 403 N.E.2d at 82-83.

															[ Footnote 4/2 ]

															Lance does not appear to have behaved suspiciously in flying
down to Florida. He made a reservation in his own name and gave an
accurate home phone number to the airlines. Cf. Florida v.
Royer, 460 U. S. 491 , 460 U. S. 493 ,
n. 2 (1983); United States v. Mendenhall, 446 U.
S. 544 , 446 U. S. 548 (1980) (Stewart, J., announcing the judgment). And Detective
Mader's affidavit does not report that he did any of the other
things drug couriers are notorious for doing, such as paying for
the ticket in cash, Royer, 460 U.S. at 460 U. S. 493 ,
n. 2, dressing casually, ibid., looking pale and nervous, ibid.; Mendenhall, supra, at 446 U. S. 548 ,
improperly filling out baggage tags, Royer, 460 U.S. at 460 U. S. 493 ,
n. 2, carrying American Tourister luggage, ibid., not
carrying any luggage, Mendenhall, 446 U.S. at 446 U. S.
564 -565 (POWELL, J., concurring in part and concurring
in judgment), or changing airlines en route, ibid. [ Footnote 4/3 ]

															Detective Mader's affidavit hinted darkly that the couple had
set out upon "that interstate highway commonly used by travelers to
the Chicago area." But the same highway is also commonly used by
travelers to Disney World, Sea World, and Ringling Brothers and
Barnum and Bailey Circus World. It is also the road to Cocoa Beach,
Cape Canaveral, and Washington, D.C. I would venture that, each
year, dozens of perfectly innocent people fly to Florida, meet a
waiting spouse, and drive off together in the family car.

															[ Footnote 4/4 ]

															The Court purports to rely on the proposition that,

															"if the [anonymous] informant could predict with considerable accuracy the somewhat unusual travel
plans of the Gateses, he probably also had a reliable basis
for his statements that the Gateses kept a large quantity of drugs
in their home." Ante at 462 U. S.
245 -246, n. 14 (emphasis added). Even if this syllogism
were sound, but see Spinelli v. United States, 393 U. S. 410 , 393 U. S. 427 (1969) (WHITE, J., concurring), its premises are not met in this
case.

															[ Footnote 4/5 ]

															The officers did not enter the unoccupied house as soon as the
warrant issued; instead, they waited until the Gates returned. It
is unclear whether they waited because they wanted to execute the
warrant without unnecessary property damage or because they had
doubts about whether the informant's tip was really valid. In
either event their judgment is to be commended.

															[ Footnote 4/6 ]

															It is a truism that

															"a search warrant is valid only if probable cause has been shown
to the magistrate, and that an inadequate showing may not be
rescued by post-search testimony on information known to the
searching officers at the time of the search." Rice v. Wolff, 513 F.2d 1280, 1287 (CA8 1975). See
Coolidge v. New Hampshire, 403 U. S. 443 , 403 U. S.
450 -451 (1971); Whiteley v. Warden, 401 U. S. 560 , 401 U. S. 565 ,
n. 8 (1971); Aguilar v. Texas, 378 U.
S. 108 , 378 U. S. 109 ,
n. 1 (1964); Jones v. United States, 357 U.
S. 493 , 357 U. S.
497 -498 (1958); Giordenello v. United States, 357 U. S. 480 , 357 U. S. 486 (1958); Taylor v. United States, 286 U. S.
1 , 286 U. S. 6 (1932); Agnello v. United States, 269 U. S.
20 , 269 U. S. 33 (1925).

															[ Footnote 4/7 ] Draper v. United States, 358 U.
S. 307 (1959), affords no support for today's holding.
That case did not involve an anonymous informant. On the contrary,
as the Court twice noted, Mr. Hereford was "employed for that
purpose, and [his] information had always been found accurate and
reliable." Id. at 358 U. S. 313 ; see id. at 358 U. S. 309 .
In this case, the police had no prior experience with the
informant, and some of his or her information in this case was
unreliable and inaccurate.

															[ Footnote 4/8 ]

															The Court holds that what were heretofore considered two
independent "prongs" -- "veracity" and "basis of knowledge" -- are
now to be considered together as circumstances whose totality must
be appraised. Ante at 462 U. S.
233 .

															"[A] deficiency in one may be compensated for, in determining
the overall reliability of a tip, by a strong showing as to the
other, or by some other indicia of reliability." Ibid. Yet in this case, the lower courts found neither
factor present. 85 Ill. 2d at 390, 423 N.E.2d at 893. And the
supposed "other indicia" in the affidavit take the form of activity
that is not particularly remarkable. I do not understand how the
Court can find that the "totality" so far exceeds the sum of its
"circumstances."

Summary: The Supreme Court ruled that a search warrant can be issued based on an anonymous tip if the information provided is detailed enough to indicate a reliable basis of knowledge and can be corroborated by the police. In this case, the anonymous letter provided specific details about the Gateses' travel plans and drug activities, which were verified by the police through their investigation and surveillance. However, Justice White, in his dissent, argued that the police's independent corroboration of innocent activity was not sufficient to establish probable cause.