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															SUPREME COURT OF THE UNITED STATES

															_________________

															No. 18–6135

															_________________

															JAMES K. KAHLER, PETITIONER v. KANSAS

															on writ of certiorari to the supreme court of
kansas

															[March 23, 2020]

															Justice Kagan delivered the opinion of the
Court.

															This case is about Kansas’s treatment of a
criminal defendant’s insanity claim. In Kansas, a defendant can
invoke mental illness to show that he lacked the requisite mens
rea (intent) for a crime. He can also raise mental illness
after conviction to justify either a reduced term of imprisonment
or commitment to a mental health facility. But Kansas, unlike many
States, will not wholly exonerate a defendant on the ground that
his illness prevented him from recognizing his criminal act as
morally wrong. The issue here is whether the Constitution’s Due
Process Clause forces Kansas to do so—otherwise said, whether that
Clause compels the acquittal of any defendant who, because of
mental illness, could not tell right from wrong when committing his
crime. We hold that the Clause imposes no such requirement.

															I

															A

															In Clark v. Arizona , 548 U.S.
735 , 749 (2006), this Court catalogued state insanity defenses,
counting four “strains variously combined to yield a diversity of
American standards” for when to absolve mentally ill defendants of
criminal culpability. The first strain asks about a defendant’s
“cognitive capacity”—whether a mental illness left him “unable to
understand what he [was] doing” when he committed a crime. Id. , at 747, 749. The second examines his “moral
capacity”—whether his illness rendered him “un- able to understand
that his action [was] wrong.” Ibid. Those two inquiries, Clark explained, appeared as alternative pathways to
acquittal in the landmark English ruling M’Naghten’s Case ,
10 Cl. & Fin. 200, 8 Eng. Rep. 718 (H. L. 1843), as well as in
many follow-on American decisions and statutes: If the defendant
lacks either cognitive or moral capacity, he is not criminally
responsible for his behavior. Yet a third “building block[ ]”
of state insanity tests, gaining popularity from the mid-19th
century on, focuses on “volitional incapacity”—whether a
defendant’s mental illness made him subject to
“irresistible[ ] impulse[s]” or otherwise unable to
“control[ ] his actions.” Clark , 548 U. S., at
749, 750, n. 11; see, e.g. , Parsons v. State , 81 Ala. 577, 597, 2 So. 854, 866–867 (1887). And
bringing up the rear, in Clark ’s narration, the
“product-of-mental-illness test” broadly considers whether the
defendant’s criminal act stemmed from a mental disease. 548
U. S., at 749–750.

															As Clark explained, even that taxonomy
fails to capture the field’s complexity. See id. , at 750,
n. 11. Most notable here, M’Naghten ’s “moral capacity”
prong later produced a spinoff, adopted in many States, that does
not refer to morality at all. Instead of examining whether a
mentally ill defendant could grasp that his act was immoral ,
some jurisdictions took to asking whether the defendant could
understand that his act was illegal . Compare, e.g. , People v. Schmidt , 216 N.Y. 324, 333–334, 110 N.E.
945, 947 (1915) (Cardozo, J.) (asking about moral right and wrong),
with, e.g. , State v. Hamann , 285 N.W.2d 180 , 183 (Iowa 1979) (substituting ideas of legal
right and wrong). That change in legal standard matters when a
mentally ill defendant knew that his act violated the law yet
believed it morally justified. See, e.g. , Schmidt ,
216 N. Y., at 339, 110 N. E., at 949; People v. Serravo , 823 P.2d 128 , 135 (Colo. 1992).[ 1 ]

															Kansas law provides that “[i]t shall be a
defense to a prosecution under any statute that the defendant, as a
result of mental disease or defect, lacked the culpable mental
state required as an element of the offense charged.” Kan. Stat.
Ann. §21–5209 (2018 Cum. Supp.).[ 2 ] Under that statute, a defendant may introduce any
evidence of any mental illness to show that he did not have the
intent needed to commit the charged crime. Suppose, for example,
that the defendant shot someone dead and goes on trial for murder.
He may then offer psychiatric testimony that he did not understand
the function of a gun or the consequences of its use—more generally
stated, “the nature and quality” of his actions. M’Naghten ,
10 Cl. & Fin., at 210, 8 Eng. Rep., at 722. And a jury
crediting that testimony must acquit him. As everyone here agrees,
Kansas law thus uses M’Naghten ’s “cognitive capacity”
prong—the inquiry into whether a mentally ill defendant could
comprehend what he was doing when he committed a crime. See Brief
for Petitioner 41; Brief for Respondent 31; Brief for United States
as Amicus Curiae 18. If the defendant had no such capacity,
he could not form the requisite intent—and thus is not criminally
responsible.

															At the same time, the Kansas statute provides
that “[m]ental disease or defect is not otherwise a defense.”
§21–5209. In other words, Kansas does not recognize any additional
way that mental illness can produce an acquittal.[ 3 ] Most important for this case, a
defendant’s moral incapacity cannot exonerate him, as it would if
Kansas had adopted both original prongs of M’Naghten .
Assume, for example, that a defendant killed someone because of an
“insane delusion that God ha[d] ordained the sacrifice.” Schmidt , 216 N. Y., at 339, 110 N. E., at 949. The
defendant knew what he was doing (killing another person), but he
could not tell moral right from wrong; indeed, he thought the
murder morally justified. In many States, that fact would preclude
a criminal conviction, although it would almost always lead to
commitment in a mental health facility. In Kansas, by contrast,
evidence of a mentally ill defendant’s moral incapacity—or indeed,
of anything except his cognitive inability to form the needed mens rea —can play no role in determining guilt.

															That partly closed-door policy changes once a
verdict is in. At the sentencing phase, a Kansas defendant has wide
latitude to raise his mental illness as a reason to judge him not
fully culpable and so to lessen his punishment. See
§§21–6815(c)(1)(C), 21–6625(a). He may present evidence (of the
kind M’Naghten deemed relevant) that his disease made him
unable to understand his act’s moral wrongness—as in the example
just given of religious delusion. See §21–6625(a) . Or he may
try to show (in line with M’Naghten ’s spinoff ) that
the illness prevented him from “appreciat[ing] the [conduct’s]
criminality.” §21–6625(a)(6). Or again, he may offer testimony
(here invoking volitional incapacity) that he simply could not
“conform [his] conduct” to legal restraints. Ibid. Kansas
sentencing law thus provides for an individualized determination of
how mental illness, in any or all of its aspects, affects
culpability. And the same kind of evidence can persuade a court to
place a defendant who needs psychiatric care in a mental health
facility rather than a prison. See §22–3430. In that way, a
defendant in Kansas lacking, say, moral capacity may wind up in the
same kind of institution as a like defendant in a State that would
bar his conviction.

															B

															This case arises from a terrible crime. In
early 2009, Karen Kahler filed for divorce from James Kahler and
moved out of their home with their two teenage daughters and
9-year-old son. Over the following months, James Kahler became more
and more distraught. On Thanksgiving weekend, he drove to the home
of Karen’s grandmother, where he knew his family was staying.
Kahler entered through the back door and saw Karen and his son. He
shot Karen twice, while allowing his son to flee the house. He then
moved through the residence, shooting Karen’s grandmother and each
of his daughters in turn. All four of his victims died. Kahler
surrendered to the police the next day and was charged with capital
murder.

															Before trial, Kahler filed a motion arguing that
Kansas’s treatment of insanity claims violates the Fourteenth
Amendment’s Due Process Clause. Kansas, he asserted, had
“unconstitutionally abolished the insanity defense” by allowing the
conviction of a mentally ill person “who cannot tell the difference
between right and wrong.” App. 11–12. The trial court denied the
motion, leaving Kahler to attempt to show through psychiatric and
other testimony that severe depression had prevented him from
forming the intent to kill. See id. , at 16; §21–5209. The
jury convicted Kahler of capital murder. At the penalty phase, the
court permitted Kahler to offer additional evidence of his mental
illness and to argue in whatever way he liked that it should
mitigate his sentence. The jury still decided to impose the death
penalty.

															Kahler appealed, again challenging the
constitutionality of Kansas’s approach to insanity claims. The
Kansas Supreme Court rejected his argument, relying on an earlier
precedential decision. See 307 Kan. 374, 400–401, 410 P.3d 105,
124–125 (2018) (discussing State v. Bethel , 275 Kan.
456, 66 P.3d 840 (2003)). There, the court denied that any single
version of the insanity defense is so “ingrained in our legal
system” as to count as “fundamental.” Id. , at 473, 66
P. 3d, at 851. The court thus found that “[d]ue process does
not mandate that a State adopt a particular insanity test.” Ibid. Kahler then asked this Court to decide whether
the Due Process Clause requires States to provide an insanity
defense that acquits a defendant who could not “distinguish right
from wrong” when committing his crime—or, otherwise put, whether
that Clause requires States to adopt the moral-incapacity test from M’Naghten . Pet. for Cert. 18. We granted certiorari, 586
U. S. ___ (2019), and now hold it does not.[ 4 ]

															II

															A

															A challenge like Kahler’s must surmount a high
bar. Under well-settled precedent, a state rule about criminal
liability—laying out either the elements of or the defenses to a
crime—violates due process only if it “offends some principle of
justice so rooted in the traditions and conscience of our people as
to be ranked as fundamental.” Leland v. Oregon , 343 U.S.
790 , 798 (1952) (internal quotation marks omitted). Our primary
guide in applying that standard is “historical practice.” Montana v. Egelhoff , 518 U.S.
37 , 43 (1996) (plurality opinion). And in assessing that
practice, we look primarily to eminent common-law authorities
(Blackstone, Coke, Hale, and the like), as well as to early English
and American judicial decisions. See, e.g. , id. , at
44–45; Patterson v. New York , 432
U.S. 197 , 202 (1977). The question is whether a rule of
criminal responsibility is so old and venerable—so entrenched in
the central values of our legal system—as to prevent a State from
ever choosing another. An affirmative answer, though not unheard
of, is rare. See, e.g. , Clark , 548 U. S., at 752
(“[T]he conceptualization of criminal offenses” is mostly left to
the States).

															In Powell v. Texas , 392 U.S.
514 (1968), this Court explained why. There, Texas declined to
recognize “chronic alcoholism” as a defense to the crime of public
drunkenness. Id. , at 517 (plurality opinion). The Court
upheld that decision, emphasizing the paramount role of the States
in setting “standards of criminal responsibility.” Id. , at
533. In refusing to impose “a constitutional doctrine” defining
those standards, the Court invoked the many “interlocking and
overlapping concepts” that the law uses to assess when a person
should be held criminally accountable for “his antisocial deeds.” Id. , at 535–536. “The doctrines of actus reus , mens rea , insanity, mistake, justification, and duress”—the
Court counted them off—reflect both the “evolving aims of the
criminal law” and the “changing religious, moral, philosophical,
and medical views of the nature of man.” Id. , at 536. Or
said a bit differently, crafting those doctrines involves balancing
and rebalancing over time complex and oft-competing ideas about
“social policy” and “moral culpability”—about the criminal law’s
“practical effectiveness” and its “ethical foundations.” Id. , at 538, 545, 548 (Black, J., concurring). That
“constantly shifting adjustment” could not proceed in the face of
rigid “[c]onstitution[al] formulas.” Id. , at 536–537
(plurality opinion). Within broad limits, Powell thus
concluded, “doctrine[s] of criminal responsibility” must remain
“the province of the States.” Id. , at 534, 536.

															Nowhere has the Court hewed more closely to that
view than in addressing the contours of the insanity defense. Here,
uncertainties about the human mind loom large. See, e.g. , Ake v. Oklahoma , 470 U.S.
68 , 81 (1985) (“[P]sychiatrists disagree widely and frequently
on what constitutes mental illness, on [proper] diagnos[es, and] on
cure and treatment”). Even as some puzzles get resolved, others
emerge. And those perennial gaps in knowledge intersect with
differing opinions about how far, and in what ways, mental illness
should excuse criminal conduct. See Clark , 548 U. S.,
at 749–752 (canvassing how those competing views produced a wealth
of insanity tests); supra , at 1–2. “This whole problem,” we
have noted, “has evoked wide disagreement.” Leland , 343
U. S., at 801. On such unsettled ground, we have hesitated to
reduce “experimentation, and freeze [the] dialogue between law and
psychiatry into a rigid constitutional mold.” Powell , 392
U. S., at 536–537. Indeed, while addressing the demand for an
alcoholism defense in Powell , the Court pronounced—as
something close to self-evident—that “[n]othing could be less
fruitful” than to define a specific “insanity test in
constitutional terms.” Id. , at 536.

															And twice before we have declined to do so. In Leland v. Oregon , a criminal defendant challenged as
a violation of due process the State’s use of the moral-incapacity
test of insanity—the very test Kahler now asks us to require. See
343 U. S., at 800–801. According to the defendant, Oregon
instead had to adopt the volitional-incapacity (or
irresistible-impulse) test to comply with the Constitution. See ibid. ; supra , at 2. We rejected that argument.
“[P]sychiatry,” we first noted, “has made tremendous strides since
[the moral-incapacity] test was laid down in M’Naghten’s
Case ,” implying that the test seemed a tad outdated. 343
U. S., at 800–801. But still, we reasoned, “the progress of
science has not reached a point where its learning” would demand
“eliminat[ing] the right and wrong test from [the] criminal law.” Id. , at 801. And anyway, we continued, the “choice of a test
of legal sanity involves not only scientific knowledge but
questions of basic policy” about when mental illness should absolve
someone of “criminal responsibility.” Ibid. The matter was
thus best left to each State to decide on its own. The dissent
agreed (while parting from the majority on another ground): “[I]t
would be indefensible to impose upon the States[ ] one test
rather than another for determining criminal culpability” for the
mentally ill, “and thereby to displace a State’s own choice.” Id. , at 803 (opinion of Frankfurter, J.).

															A half-century later, we reasoned similarly in Clark . There, the defendant objected to Arizona’s decision
to discard the cognitive-incapacity prong of M’Naghten and
leave in place only the moral-incapacity one—essentially the
flipside of what Kansas has done. Again, we saw no due process
problem. Many States, we acknowledged, allowed a defendant to show
insanity through either prong of M’Naghten . See 548
U. S., at 750. But we denied that this approach “represents
the minimum that a government must provide.” Id. , at 748. In
so doing, we invoked the States’ traditional “capacity to define
crimes and defenses,” and noted how views of mental illness had
been particularly “subject to flux and disagreement.” Id. ,
at 749, 752. And then we surveyed the disparate ways that state
laws had historically excused criminal conduct because of mental
disease—those “strains variously combined to yield a diversity of
American standards.” See id. , at 749–752; supra , at
1–2. The takeaway was “clear”: A State’s “insanity rule[ ] is
substantially open to state choice.” Clark , 548 U. S.,
at 752. Reiterating Powell ’s statement, Clark held
that “no particular” insanity test serves as “a baseline for due
process.” 548 U. S., at 752. Or said just a bit differently,
that “due process imposes no single canonical formulation of legal
insanity.” Id. , at 753.

															B

															Yet Kahler maintains that Kansas’s treatment
of insanity fails to satisfy due process. He sometimes makes his
argument in the broadest of strokes, as he did before trial. See supra , at 5. Kansas, he then contends, has altogether
“abolished the insanity defense,” in disregard of hundreds of years
of historical practice. Brief for Petitioner 39. His central claim,
though, is more confined. It is that Kansas has impermissibly
jettisoned the moral-incapacity test for insanity. See id. ,
at 12, 23. As earlier noted, both Clark and Leland described that test as coming from M’Naghten . See 548
U. S., at 749; 343 U. S., at 801; supra , at 2, 8.
But according to Kahler (and the dissent), the moral-incapacity
inquiry emerged centuries before that decision, thus forming part
of the English common-law heritage this country inherited. See
Brief for Petitioner 21, 42; post , at 4–14 (opinion of
Breyer, J.). And the test, he claims, served for all that time—and
continuing into the present—as the touchstone of legal insanity: If
a defendant could not understand that his act was morally wrong,
then he could not be found criminally liable. See Brief for
Petitioner 20–23; see also post , at 15. So Kahler concludes
that the moral-incapacity standard is a “principle of justice so
rooted in the traditions and conscience of our people as to be
ranked as fundamental.” Leland , 343 U. S., at 798; see supra , at 6. In essence—and contra Clark —that test is the “single canonical formulation of legal insanity” and
thus the irreducible “baseline for due process.” 548 U. S., at
752–753; see supra , at 9.[ 5 ]

															One point, first, of agreement: Kahler is right
that for hundreds of years jurists and judges have recognized
insanity (however defined) as relieving responsibility for a crime.
“In criminal cases therefore,” Sir William Blackstone wrote,
“lunatics are not chargeable for their own acts, if committed when
under these incapacities.” 4 Commentaries on the Laws of England 24
(1769). Sir Edward Coke even earlier explained that in criminal
cases, “the act and wrong of a mad man shall not be imputed to
him.” 2 Institutes of the Laws of England §405, p. 247b (1628)
(Coke). And so too Henry de Bracton thought that a “madman” could
no sooner be found criminally liable than a child. 2 Bracton on
Laws and Customs of England 384 (S. Thorne transl. 1968) (Bracton).
That principle of non-culpability appeared in case after case
involving allegedly insane defendants, on both sides of the
Atlantic. “The defense of insanity[ ] is a defense for all
crimes[,] from the highest to the lowest,” said the Court in Old
Bailey. Trial of Samuel Burt (July 19, 1786), in 6
Proceedings in the Old Bailey 874 (E. Hodgson ed. 1788) (Old Bailey
Proceedings). Repeated Justice Story, when riding circuit: “In
general, insanity is an excuse for the commission of every crime,
because the party has not the possession of that reason, which
includes responsibility.” United States v. Drew , 25
F. Cas. 913 (No. 14,993) (CC Mass. 1828); see also, e.g. , State v. Marler , 2 Ala. 43, 49 (1841) (“If the
prisoner was insane, he was not an accountable being”); Cornwell v. State , 8 Tenn. 147, 156 (1827)
(“[P]erfect madness” will “free a man from punishment for crime”).
We have not found a single case to the contrary.

															But neither do we think Kansas departs from that
broad principle. First, Kansas has an insanity defense negating
criminal liability—even though not the type Kahler demands. As
noted earlier, Kansas law provides that it is “a defense to a
prosecution” that “the defendant, as a result of mental disease or
defect, lacked the culpable mental state required” for a crime.
§21–5209; see supra , at 3. That provision enables a
defendant to present psychiatric and other evidence of mental
illness to defend himself against a criminal charge. More
specifically, the defendant can use that evidence to show that his
illness left him without the cognitive capacity to form the
requisite intent. See supra , at 3. Recall that such a
defense was exactly what the defendant in Clark wanted, in
preference to Arizona’s moral-incapacity defense: His
(unsuccessful) appeal rested on the trial court’s exclusion of
psychiatric testimony to show that he lacked the relevant mens
rea . See 548 U. S., at 745–747; supra , at 9. Here,
Kahler could do what Clark could not—try to show through such
testimony that he had no intent to kill. Of course, Kahler would
have preferred Arizona’s kind of insanity defense (just as Clark
would have liked Kansas’s). But that does not mean that Kansas (any
more than Arizona) failed to offer any insanity defense at all.

															Second, and significantly, Kansas permits a
defendant to offer whatever mental health evidence he deems
relevant at sentencing. See §§21–6815(c)(1)(C), 21–6625(a); supra , at 4. A mentally ill defendant may argue there that
he is not blameworthy because he could not tell the difference
between right and wrong. Or, because he did not know his conduct
broke the law. Or, because he could not control his behavior. Or,
because of anything else. In other words, any manifestation of
mental illness that Kansas’s guilt-phase insanity defense
disregards—including the moral incapacity Kahler highlights—can
come in later to mitigate culpability and lessen punishment. And
that same kind of evidence can persuade a judge to replace any
prison term with commitment to a mental health facility. See
§22–3430; supra , at 4–5. So as noted above, a defendant
arguing moral incapacity may well receive the same treatment in
Kansas as in States that would acquit—and, almost certainly,
commit—him for that reason. See supra , at 4–5. In sum,
Kansas does not bar, but only channels to sentencing, the mental
health evidence that falls outside its intent-based insanity
defense. When combined with Kansas’s allowance of mental health
evidence to show a defendant’s inability to form criminal intent,
that sentencing regime defeats Kahler’s charge that the State has
“abolish[ed] the insanity defense entirely.”[ 6 ] Brief for Petitioner 39.

															So Kahler can prevail here only if he can show
(again, contra Clark ) that due process demands a specific
test of legal insanity—namely, whether mental illness prevented a
defendant from understanding his act as immoral. Kansas, as we have
explained, does not use that type of insanity rule. See supra , at 3–4. If a mentally ill defendant had enough
cognitive function to form the intent to kill, Kansas law directs a
conviction even if he believed the murder morally justified. In
Kansas’s judgment, that delusion does not make an intentional
killer entirely blameless. See Brief for Respondent 40. Rather than
eliminate, it only lessens the defendant’s moral culpability. See ibid. And sentencing is the appropriate place to consider
mitigation: The decisionmaker there can make a nuanced evaluation
of blame, rather than choose, as a trial jury must, between all and
nothing. See ibid. In any event, so Kansas thinks.[ 7 ] Those views are contested and
contestable; other States—many others—have made a different choice.
But Kahler must show more than that. He must show that adopting the
moral-incapacity version of the insanity rule is not a choice at
all—because, again, that version is “so rooted in the traditions
and conscience of our people as to be ranked as fundamental.” Leland , 343 U. S., at 798. And he cannot. The
historical record is, on any fair reading, complex—even messy. As
we will detail, it reveals early versions of not only Kahler’s
proposed standard but also Kansas’s alternative.

															Early commentators on the common law proposed
various formulations of the insanity defense, with some favoring a
morality inquiry and others a mens rea approach. Kahler
cites William Lambard’s 16th-century treatise defining a “mad man”
as one who “hath no knowledge of good nor evil” (the right and
wrong of the day). Eirenarcha, ch. 21, p. 218 (1581). He
likewise points to William Hawkins’s statement, over a hundred
years later, that a “lunatick[ ]” is not punishable because
“under a natural disability of distinguishing between good and
evil.” 1 Pleas of the Crown §1, p. 2 (1716) (capitalization
omitted). Both true enough. But other early versions of the
insanity test—and from a more famous trio of jurists—demanded the
kind of cognitive impairment that prevented a defendant from
understanding the nature of his acts, and thus intending his crime.
Henry de Bracton’s 13th-century treatise gave rise to what became
known as the “wild beast” test. See J. Biggs, The Guilty Mind 82
(1955). Used for hundreds of years, it likened a “madman” to an
“animal[ ] which lack[s] reason” and so could not have “the
intention to injure.” Bracton 384; see ibid. (A “madman”
cannot commit a crime because “[i]t is will and purpose which mark”
misdeeds). Sir Edward Coke similarly linked the definition of
insanity to a defendant’s inability to form criminal intent. He
described a legally insane person in 1628 as so utterly “without
his mind or discretion” that he could not have the needed mens
rea . 2 Coke §405, at 247b. So too Lord Matthew Hale a century
later. He explained that insanity involves “a total alienation of
the mind or perfect madness,” such that a defendant could not act
“ animo felonico ,” meaning with felonious intent. 1 Pleas of
the Crown, ch. 4, pp. 30, 37 (1736); see id. , at 37
(“[F]or being under a full alienation of mind, he acts not per electionem or intentionem [by choice or
intent]”).[ 8 ]

															Quite a few of the old common-law cases
similarly stressed the issue of cognitive capacity. To be sure,
even these cases included some references to the ability to tell
right from wrong (and the dissent eagerly cherry-picks every one of
them). But the decisions’ overall focus was less on whether a
defendant thought his act moral than on whether he had the ability
to do much thinking at all. In the canonical case of Rex v. Arnold , 16 How. St. Tr. 695 (1724), for example, the jury
charge descended straight from Bracton:

															“[I]t is not every kind of frantic humour
or something unaccountable in a man’s actions, that points him out
to be such a madman as is to be exempted from punishment: it must
be a man that is totally deprived of his understanding and memory,
and doth not know what he is doing, no more than an infant, than a
brute, or a wild beast.” Id. , at 764–765.

															And the court offered an accompanying test
linking that lack of reason to mens rea : If a man is
“deprived of his reason, and consequently of his intention, he
cannot be guilty.” Id. , at 764; see ibid. (defining a
“madman” as a “person that hath no design”); see also Trial of
William Walker (Apr. 21, 1784), in 4 Old Bailey Proceedings
544, 547 (asking whether the defendant had a “distemper of mind
which had deprived him of the use of his reason” or instead whether
“he knew what he was doing [and] meant to do it”); Beverley’s
Case , 4 Co. Rep. 123b, 124b, 76 Eng. Rep. 1118, 1121 (K. B.
1603) (asking whether a man “is deprived of reason and
understanding” and so “cannot have a felonious intent”). The House
of Lords used much the same standard in Rex v. Lord
Ferrers , 19 How. St. Tr. 886 (1760), when sitting in judgment
on one of its members. There, the Solicitor General told the Lords
to address “the capacity and intention of the noble prisoner.” Id. , at 948. Relying heavily on Hale’s treatise, he defined
the legally insane as suffering from an “alienation of mind” and a
“total[ ] want of reason.” Id. , at 947. And in
recapping the evidence on that issue, he asked about the
defendant’s intention: “Did [Ferrers] proceed with deliberation?
Did he know the consequences” of his act? Id. , at
948.[ 9 ]

															In such cases, even the language of morality
mostly worked in service of the emphasis on cognition and mens
rea . The idea was that if a defendant had such a “total[ ]
want of reason” as to preclude moral thinking, he could not
possibly have formed the needed criminal intent. Id. , at
947. Lord Chief Justice Mansfield put the point neatly in Bellingham’s Case , 1 G. Collinson, Treatise on the Law
Concerning Idiots, Lunatics, and Other Persons Non Compotes Mentis
636 (1812) (Collinson). He instructed the jury:

															“If a man were deprived of all power of
reasoning, so as not to be able to distinguish whether it was right
or wrong to commit the most wicked transaction, he could not
certainly do an act against the law. Such a man, so destitute of
all power of judgment, could have no intention at all.” Id. ,
at 671.

															On that account, moral incapacity was a
byproduct of the kind of cognitive breakdown that precluded finding mens rea , rather than a self-sufficient test of insanity.
See also Rex v. Offord , 5 Car. & P. 168, 169, 172
Eng. Rep. 924, 925 (N. P. 1831) (“express[ing] complete accordance
in the observations of th[e] learned Judge” in Bellingham ).
Or said another way, a mentally ill defendant’s inability to
distinguish right from wrong, rather than independently producing
an insanity acquittal, served as a sign—almost a kind of
evidence—that the defendant lacked the needed criminal intent.

															Other early common-law cases do not adopt the mens rea approach—but neither can they sustain Kahler’s
position. Kahler relies mainly on Hadfield’s Case , 27 How.
St. Tr. 1281 (1800), to show that common-law courts would acquit a
mentally ill defendant who understood the nature of his act, but
believed it moral. See Reply Brief 4. There, the defendant had
deliberately set out to assassinate King George III on the view
that doing so would bring about the Second Coming. See 27 How. St.
Tr., at 1322. The judge instructed the jury that the defendant was
so “deranged” as to make acquittal appropriate. Id. , at
1353. Maybe, as Kahler argues, that directive stemmed from the
defendant’s inability to tell right from wrong. But the judge never
used that language, or stated any particular legal standard, so it
is hard to know. Still other judges explained insanity to juries by
throwing everything against the wall—mixing notions of cognitive
incapacity, moral incapacity, and more, without trying to order,
prioritize, or even distinguish among them. See, e.g. , Regina v. Oxford , 9 Car. & P. 525, 545–548, 173
Eng. Rep. 941, 950 (N. P. 1840); Trial of Francis Parr (Jan.
15, 1787), in 2 Old Bailey Proceedings 228–229; Bowler’s
Case , 1 Collinson 674. Those decisions treat the inability to
make moral judgments more as part of an all-things-considered
assessment of legal insanity, and less as its very definition. But
even if some of them belong in Kahler’s corner, that would be far
from enough. Taken as a whole, the common-law cases reveal no
settled consensus favoring Kahler’s preferred insanity rule. And
without that, they cannot support his proposed constitutional
baseline.

															Only with M’Naghten , in 1843, did a court
articulate, and momentum grow toward accepting, an insanity defense
based independently on moral incapacity. See Clark , 548
U. S., at 749; Leland , 343 U. S., at 801; supra , at 2, 8. The M’Naghten test, as already
described, found insanity in either of two circumstances. See supra , at 1–2. A defendant was acquitted if he “labour[ed]
under such a defect of reason, from disease of the mind, [1] as not
to know the nature and quality of the act he was doing; or ,
[2] if he did know it, that he did not know he was doing what was
wrong.” 10 Cl. & Fin., at 210, 8 Eng. Rep., at 722 (emphasis
added). That test disaggregated the concepts of cognitive and moral
incapacity, so that each served as a stand-alone defense. And its
crisp two-part formulation proved influential, not only in Great
Britain but in the United States too. Over the course of the 19th
century, many States adopted the test, making it the most popular
one in the country.

															Still, Clark unhesitatingly declared:
“History shows no deference to M’Naghten that could elevate
its formula to the level of fundamental principle.” 548 U. S.,
at 749. As Clark elaborated, even M’Naghten failed to
unify state insanity defenses. See 548 U. S., at 749–752.
States continued to experiment with insanity rules, reflecting what
one court called “the infinite variety of forms [of] insanity” and
the “difficult and perplexing” nature of the defense. Roberts v. State , 3 Ga. 310, 328, 332 (1847). Some
States in the 1800s gravitated to the newly emergent “volitional
incapacity” standard, focusing on whether the defendant could at
all control his actions. Clark , 548 U. S., at 749; see, e.g. , Roberts , 3 Ga., at 331. One court viewed that
inquiry as “much more practical” than the “right and wrong test,”
which it thought often “speculative and difficult of
determination.” State v. Felter , 25 Iowa 67, 82, 84
(1868); see Leland , 343 U. S., at 801 (recognizing such
skepticism about the moral-incapacity test); supra , at 8–9.
Another prophesied that the volitional test was the one “towards
which all the modern authorities in this country[ ] are
gradually but surely tending.” Parsons , 81 Ala., at 586, 2
So., at 859. But that test, too, failed to sweep all before it:
State innovation proceeded apace. See, e.g. , State v. Pike , 49 N. H. 399, 442 (1870) (applying the “product”
test, which excuses a defendant whose crime “was the offspring or
product of mental disease”); N. D. Cent. Code Ann.
§12.1–04.1–01(1)(a) (2012) (replacing the right-from-wrong test
with an inquiry into whether the defendant’s act arose from “[a]
serious distortion of [his] capacity to recognize reality”). Much
as medical views of mental illness changed as time passed, so too
did legal views of how to account for that illness when assigning
blame.

															As earlier noted, even the States that adopted M’Naghten soon divided on what its second prong should mean.
See supra , at 2–3. Most began by asking, as Kahler does,
about a defendant’s ability to grasp that his act was immoral . See, e.g. , Wright v. State , 4
Neb. 407, 409 (1876); State v. Spencer , 21
N. J. L. 196, 201 (1846). Thus, Clark labeled M’Naghten ’s second prong a test of “moral capacity,” and
invoked the oft-used phrase “telling right from wrong” (or in older
language, good from evil) to describe its central inquiry. 548
U. S., at 747, 753; see supra , at 2. But over the
years, 16 States have reoriented the test to focus on the
defendant’s understanding that his act was illegal —that is,
legally rather than morally “wrong.”[ 10 ] They thereby excluded from the ranks of the insane
those who knew an act was criminal but still thought it right.

															Contrary to Kahler’s (and the dissent’s)
contention, that difference matters. See Reply Brief 7 (claiming
that “there is little daylight between these inquiries”); post , at 17, 21 (same). The two tests will treat some, even
though not all, defendants in opposite ways. And the defendants
they will treat differently are exactly those Kahler (and the
dissent) focus on: those who know exactly what they are doing
(including that it is against the law) but believe it morally
justified—because, say, it is commanded by God (or in the dissent’s
case, a dog). See Brief for Petitioner 15; post , at 20; Schmidt , 216 N. Y., at 339, 110 N. E., at
949.[ 11 ] A famed theorist of
criminal law put the point this way:

															“A kills B knowing that he is killing B,
and knowing that it is illegal to kill B, but under an insane
delusion that the salvation of the human race will be obtained by
. . . the murder of B[.] A’s act is a crime if the word
‘wrong’ [in M’Naghten ] means illegal. It is not a crime if
the word wrong means morally wrong.” 2 J. Stephen, History of the
Criminal Law of England, ch. 19, p. 149 (1883).

															So constitutionalizing the moral-incapacity
standard, as Kahler requests, would require striking down not only
the five state laws like Kansas’s (as the dissent at times
suggests, see post , at 16), but 16 others as well (as the
dissent eventually concedes is at least possible, see post ,
at 21). And with what justification? The emergence of M’Naghten ’s legal variant, far from raising a due process
problem, merely confirms what Clark already recognized. Even
after its articulation in M’Naghten (much less before), the
moral-incapacity test has never commanded the day. Clark ,
548 U. S., at 749.[ 12 ]

															Indeed, just decades ago Congress gave serious
consideration to adopting a mens rea approach like Kansas’s
as the federal insanity rule. See United States v. Pohlot , 827 F.2d 889, 899, and n. 9 (CA3 1987)
(describing bipartisan support for that proposal). The Department
of Justice at the time favored that version of the insanity test.
Perhaps more surprisingly, the American Medical Association did
too. And the American Psychiatric Association took no position one
way or the other. Although Congress chose in the end to adhere to
the M’Naghten rule, the debate over the bill itself reveals
continuing division over the proper scope of the insanity
defense.

															Nor is that surprising, given the nature of the
inquiry. As the American Psychiatric Association once noted,
“insanity is a matter of some uncertainty.” Insanity Defense Work
Group, Statement on the Insanity Defense, 140 Am. J. Psych. 681,
685 (1983). Across both time and place, doctors and scientists have
held many competing ideas about mental illness. And that is only
the half of it. Formulating an insanity defense also involves
choosing among theories of moral and legal culpability, themselves
the subject of recurrent controversy. At the juncture between those
two spheres of conflict and change, small wonder there has not been
the stasis Kahler sees—with one version of the insanity defense
entrenched for hundreds of years.

															And it is not for the courts to insist on any
single criterion going forward. We have made the point before, in Leland , Powell , and Clark . See supra ,
at 7–9. Just a brief reminder: “[F]ormulating a constitutional rule
would reduce, if not eliminate, [the States’] fruitful
experimentation, and freeze the developing productive dialogue
between law and psychiatry into a rigid constitutional mold.” Powell , 392 U. S., at 536–537. Or again: In a sphere of
“flux and disagreement,” with “fodder for reasonable debate about
what the cognate legal and medical tests should be,” due process
imposes no one view of legal insanity. Clark , 548
U. S., at 752–753. Defining the precise relationship between
criminal culpability and mental illness involves examining the
workings of the brain, the purposes of the criminal law, the ideas
of free will and responsibility. It is a project demanding hard
choices among values, in a context replete with uncertainty, even
at a single moment in time. And it is a project, if any is, that
should be open to revision over time, as new medical knowledge
emerges and as legal and moral norms evolve. Which is all to say
that it is a project for state governance, not constitutional
law.

															We therefore decline to require that Kansas
adopt an insanity test turning on a defendant’s ability to
recognize that his crime was morally wrong. Contrary to Kahler’s
view, Kansas takes account of mental health at both trial and
sentencing. It has just not adopted the particular insanity defense
Kahler would like. That choice is for Kansas to make—and, if it
wishes, to remake and remake again as the future unfolds. No
insanity rule in this country’s heritage or history was ever so
settled as to tie a State’s hands centuries later. For that reason,
we affirm the judgment below.

															It is so ordered. Notes 1 Another complicating
factor in Clark ’s classification scheme is that States
“limit, in varying degrees, which sorts of mental illness” can
support an insanity claim. Clark v. Arizona , 548 U.S.
735 , 750, n. 11 (2006). So even two States using the same
test for judging culpability may apply it to differently sized sets
of offenders. See infra , at 21, n. 11. 2 At the time of the crime
in this case, a materially identical provision was codified at
§22–3220 (2007). 3 Four other States
similarly exonerate a mentally ill defendant only when he cannot
understand the nature of his actions and so cannot form the
requisite mens rea . See Alaska Stat. §§12.47.010(a),
12.47.020 (2018); Idaho Code Ann. §§18–207(1), (3) (2016); Mont.
Code Ann. §46–14–102 (2019); Utah Code §76–2–305
(2017). 4 Kahler also asked us to
decide whether the Eighth Amendment requires that States make
available the moral-incapacity defense. See Pet. for Cert. 18. But
that claim is not properly before us. Kahler did not raise the
argument below, and the Kansas courts therefore did not address
it. 5 Although the dissent at
times claims to the contrary, its argument is the same. Given the
clear direction of our precedent, the dissent must purport to grant
the States “leeway” in defining legal insanity. Post , at 1.
But the entirety of the dissent’s historical analysis focuses on
the moral-incapacity standard—attempting to show, just as Kahler
does, that it both preceded and succeeded M’Naghten . See post , at 4–17. And in line with that narration, the dissent
insists on moral understanding as the indispensable criterion of
legal sanity—the sine qua non of criminal responsibility.
See, e.g. , post , at 1, 3–4, 8–9, 18–21. Indeed, the
dissent offers only one way the States have actual “leeway” to
change their insanity rules: They can “ expand upon M’Naghten ’s principles” by finding that even some who have moral capacity are insane. Post , at 22. But that
is just to say that moral capacity is the constitutional
floor—again, exactly what Kahler argues. 6 We here conclude only
that Kansas’s scheme does not abolish the insanity defense. We say
nothing, one way or the other, about whether any other scheme might
do so. 7 The dissent is therefore
wrong to suggest that Kansas’s law has become untethered from moral
judgments about culpability. See post , at 1, 3, 16–22. No
doubt, Kansas’s moral judgments differ from the dissent’s. Again,
Kansas believes that an intentional killer is not wholly blameless,
even if, for example, he thought his actions commanded by God. The
dissent, in contrast, considers Kansas’s view benighted (as maybe
some in the majority do too). But that is not a dispute, as the
dissent suggests, about whether morality should play a role
in assigning legal responsibility. It is instead a disagreement
about what morality entails—that is, about when a defendant
is morally culpable for an act like murder. See State v. Bethel , 275 Kan. 456, 465–471, 66 P.3d 840, 847–850 (2003)
(accepting Kansas’s view that “moral blameworthiness” is linked to
a defendant’s intent to kill, rather than to his ability to tell
right from wrong). And we have made clear, from Leland to Powell to Clark , that courts do not get to make such
judgments. See supra , at 7–9. Instead, the States have broad
discretion to decide who counts as blameworthy, and to weigh that
along with other factors in defining the elements of, and defenses
to, crimes. 8 The dissent tries to
recruit these three jurists to the side of the moral-incapacity
test, see post , at 5–7, but cannot succeed. Even the
carefully curated passages the dissent quotes focus on cognitive
capability rather than moral judgment. See, e.g. , post , at 5–6 (asking whether a defendant had “sense and
reason” or “understanding and liberty of will”). In so doing, they
refer to the defendant’s ability to form the requisite mens
rea , or felonious intent. See Clark , 548 U. S., at
747; supra , at 1–3. The dissent still insists all is not
lost because (it says) mens rea itself hinged at common law
on a defendant’s “moral understanding.” Post , at 8–9. Here,
the dissent infers from the use of “good-from-evil” language in
various common-law treatises and cases that moral blameworthiness
must have defined the mens rea inquiry. See ibid. But
to begin with—and to repeat the point made in the text—the most
influential treatises used little of that language, emphasizing
instead the need for a defendant to intend his act in the ordinary
sense of the term. And as we will explain, the joint presence of
references to mens rea and moral understanding in other
common-law sources involving insanity does not show that most
jurists saw the two concepts as one and the same. See infra ,
at 16–19. Some may well have viewed mens rea through a moral
prism; but others emphasized cognitive understanding in using that
term; and still others combined the moral and cognitive in diverse
ways. Which is to say that the record is far more complicated than
the dissent lets on, with jurists invoking, both within particular
sources and across all of them, a variety of ways to resolve
insanity claims. And under our long-established precedent, that
motley sort of history cannot provide the basis for a successful
due process claim. 9 Even in the face of these
instructions, the dissent claims that Arnold and Ferrers actually used the moral-incapacity test. See post , at 9–11. The assertion is based on some “good and
evil” language (in Ferrers , mostly from witnesses) appearing
in the case reports. But scholars generally agree, in line with our
view, that Arnold and Ferrers “demonstrate how
strictly” courts viewed “the criteria of insanity.” 1 N. Walker,
Crime and Insanity in England 53 (1968) (noting that the two
decisions “have often been cited” for that proposition). Kahler
himself does not dispute the point; indeed, he essentially concedes
our reading. Rather than try to make the decisions say something
they do not, he argues only that they were “outlier[s]” and “could
hardly have been less typical.” Brief for Petitioner 22, n. 5;
Reply Brief 4 (internal quotation marks omitted). But that
contrasting response fares no better. As even the dissent agrees,
these were the “seminal” common-law decisions relating to
insanity—indeed, two of only a small number in that period to make
it into official reports. Post , at 9. 10 See State v. Skaggs , 120 Ariz. 467, 472, 586 P.2d 1279 , 1284 (1978); Wallace v. State , 766
So. 2d 364, 367 (Fla. App. 2000); State v. Hamann , 285 N.W.2d 180 , 184 (Iowa 1979); Commonwealth v. Lawson , 475 Mass. 806, 811, 62 N. E. 3d 22, 28 (2016); State v. Worlock , 117 N. J. 596, 610–611, 569 A.2d 1314 , 1322 (1990); People v. Wood , 12
N.Y.2d 69, 76, 187 N.E.2d 116, 121–122 (1962); State v. Carreiro , 2013–Ohio–1103, 988 N.E.2d 21, 27 (App.); McElroy v. State , 242 S.W. 883, 884 (Tenn. 1922); McAfee v. State , 467 S.W.3d 622, 636 (Tex. Crim. App.
2015); State v. Crenshaw , 98 Wash. 2d 789 , 794–795, 659 P.2d 488 , 492–493 (1983); Ark. Code Ann. §5–2–301(6)
(2017); Ill. Comp. Stat., ch. 720, §5/6–2(a) (West 2016); Ky. Rev.
Stat. Ann. §504.020(1) (West 2016); Md. Crim. Proc. Code Ann.
§3–109(a) (2018); Ore. Rev. Stat. §161.295(1) (2019); Vt. Stat.
Ann., Tit. 13, §4801(a)(1) (2019). 11 The
great judge (later Justice) whom the dissent cites to suggest there
is no real difference between the legal wrong and moral wrong tests
wrote a lengthy opinion whose point was the opposite. Consider a
case, Judge Cardozo said: “A mother kills her infant child to whom
she has been devotedly attached. She knows the nature and quality
of the act; she knows that the law condemns it; but she is inspired
by an insane delusion that God has appeared to her and ordained the
sacrifice.” People v. Schmidt , 216 N.Y. 324, 339, 110
N.E. 945, 949 (1915). If the legal wrong test were used, Judge
Cardozo continued, “it would be the duty of a jury to hold her
responsible for the crime.” Ibid. But not if the focus was,
as in the original M’Naghten test, on moral wrong. And that
difference led the New York Court of Appeals to hold that the trial
court’s jury instruction was in error. See 216 N. Y., at 340,
110 N. E., at 950. The additional cases the dissent cites to
downplay the distinction between moral and legal wrong in fact
follow Schmidt in recognizing when they diverge. See Worlock , 117 N. J., at 611, 569 A. 2d, at 1322
(explaining that “the distinction between moral and legal wrong may
be critical” when, for example, a defendant “knowingly kill[s]
another in obedience to a command from God”); Crenshaw , 98
Wash. 2d, at 798, 659 P. 2d, at 494 (acknowledging Schmidt ’s view that even when a defendant “knows that the
law and society condemn [her] act,” she should not be held
responsible if “her free will has been subsumed by her belief in
[a] deific decree”). 12 The
diversity of American approaches to insanity is also evident in the
States’ decisions about which kinds of mental illness can support
the defense. See Clark , 548 U. S., at 750, n. 11; supra , at 3, n. 1. Some States limit the defense to
those with a “severe” mental disease. See, e.g. , Ala. Code
§13A–3–1 (2015). Others prohibit its assertion by defendants with
specific mental disorders. See, e.g. , Ariz. Rev. Stat. Ann.
§13–502 (2010) (“psychosexual” or “impulse control disorders”);
Ore. Rev. Stat. §161.295(2) (“personality disorders”). In
particular, many States follow the Model Penal Code in prohibiting
psychopaths from raising the defense. See ALI, Model Penal Code
§4.01(2), p. 163 (1985); e.g. , Ind. Code §35–41–3–6(b)
(2019) (“abnormality manifested only by repeated unlawful or
otherwise antisocial conduct”). All those limitations apply even
when the defendant’s mental illness prevented him from recognizing
that his crime was immoral. In that way too, many States have
departed from the principle that Kahler (along with the dissent)
claims the Constitution commands. SUPREME COURT OF THE UNITED STATES

															_________________

															No. 18–6135

															_________________

															JAMES K. KAHLER, PETITIONER v. KANSAS

															on writ of certiorari to the supreme court of
kansas

															[March 23, 2020]

															Justice Breyer, with whom Justice Ginsburg and
Justice Sotomayor join, dissenting.

															Like the Court, I believe that the Constitution
gives the States broad leeway to define state crimes and criminal
procedures, including leeway to provide different definitions and
standards related to the defense of insanity. But here, Kansas has
not simply redefined the insanity defense. Rather, it has
eliminated the core of a defense that has existed for centuries:
that the defendant, due to mental illness , lacked the mental
capacity necessary for his conduct to be considered morally
blameworthy. Seven hundred years of Anglo-American legal history,
together with basic principles long inherent in the nature of the
criminal law itself, convince me that Kansas’ law “ ‘offends
. . . principle[s] of justice so rooted in the traditions
and conscience of our people as to be ranked as
fundamental.’ ” Leland v. Oregon , 343 U.S.
790 , 798 (1952) (quoting Snyder v. Massachusetts , 291 U.S.
97 , 105 (1934)).

															I

															A much-simplified example will help the reader
understand the conceptual distinction that is central to this case.
Consider two similar prosecutions for murder. In Prosecution One,
the accused person has shot and killed another person. The evidence
at trial proves that, as a result of severe mental illness, he
thought the victim was a dog. Prosecution Two is similar but for
one thing: The evidence at trial proves that, as a result of severe
mental illness, the defendant thought that a dog ordered him to
kill the victim. Under the insanity defense as traditionally
understood, the government cannot convict either defendant. Under
Kansas’ rule, it can convict the second but not the first.

															To put the matter in more explicitly legal
terms, consider the most famous statement of the traditional
insanity defense, that contained in M’Naghten’s Case , 10 Cl.
& Fin. 200, 8 Eng. Rep. 718 (H. L. 1843). Lord Chief Justice
Tindal, speaking for a majority of the judges of the common-law
courts, described the insanity defense as follows:

															“[T]o establish a defence on the ground of
insanity, it must be clearly proved that, at the time of the
committing of the act, the party accused was labouring under such a
defect of reason, from disease of the mind, [1] as not to know the
nature and quality of the act he was doing; or, [2] if he did know
it, that he did not know he was doing what was wrong.” Id. ,
at 210, 8 Eng. Rep., at 722.

															The first prong (sometimes referred to as
“cognitive incapacity”) asks whether the defendant knew what he was
doing. This prong corresponds roughly to the modern concept of mens rea for many offenses. The second (sometimes referred
to as “moral incapacity”) goes further. It asks, even if the
defendant knew what he was doing, did he have the capacity to know
that it was wrong? Applying this test to my example, a court would
find that both defendants successfully established an insanity
defense. Prosecution One (he thought the victim was a dog) falls
within M’Naghten ’s first prong, while Prosecution Two (he
thought the dog ordered him to do it) falls within its second
prong.

															In Kansas’ early years of statehood, its courts
recognized the M’Naghten test as the “cardinal rule of
responsibility in the criminal law.” State v. Nixon ,
32 Kan. 205, 206, 4 P. 159, 160 (1884). Kansas “steadfastly adhered
to that test” for more than a century. State v. Baker , 249 Kan. 431, 449–450, 819 P.2d 1173 , 1187 (1991). But in 1995, Kansas
“ ‘legislatively abolish[ed] the insanity defense.’ ” State v. Jorrick , 269 Kan. 72, 82, 4 P.3d 610, 617
(2000) (quoting Rosen, Insanity Denied: Abolition of the Insanity
Defense in Kansas, 8 Kan. J. L. & Pub. Pol’y 253, 254–255
(1997)). Under the new provision, a criminal defendant’s mental
disease or defect is relevant to his guilt or innocence only
insofar as it shows that he lacked the intent defined as an element
of the offense, or mens rea . If the defendant acted with the
required level of intent, then he has no defense based on mental
illness. Kan. Stat. Ann. §21–5209 (2018 Cum. Supp.).

															Under Kansas’ changed law, the defendant in
Prosecution One could defend against the charge by arguing that his
mental illness prevented him from forming the mental state required
for murder (intentional killing of a human being)—just as any
defendant may attempt to rebut the State’s prima facie case for
guilt. The defendant in Prosecution Two has no defense. Because he
acted with the requisite level of intent, he must be convicted
regardless of any role his mental illness played in his conduct.
See 307 Kan. 374, 401, 410 P.3d 105, 125 (2018) (acknowledging that
Kansas’ mens rea approach “allows conviction of an
individual who had no capacity to know that what he or she was
doing was wrong”).

															I do not mean to suggest that M’Naghten ’s
particular approach to insanity is constitutionally required. As we
have said, “[h]istory shows no deference to M’Naghten .” Clark v. Arizona , 548
U.S. 735 , 749 (2006). M’Naghten ’s second prong is merely
one way of describing something more fundamental. Its basic insight
is that mental illness may so impair a person’s mental capacities
as to render him no more responsible for his actions than a young
child or a wild animal. Such a person is not properly the subject
of the criminal law. As I shall explain in the following section,
throughout history, the law has attempted to embody this principle
in a variety of ways. As a historical matter, M’Naghten is
by far its most prominent expression, but not its exclusive one.
Other ways of capturing it may well emerge in the future. The
problem with Kansas’ law is that it excises this fundamental
principle from its law entirely.

															II

															The Due Process Clause protects those
“ ‘principle[s] of justice so rooted in the traditions and
conscience of our people as to be ranked as fundamental.’ ” Leland , 343 U. S., at 798. Our “primary guide” in
determining whether a principle of justice ranks as fundamental is
“historical practice.” Montana v. Egelhoff , 518 U.S.
37 , 43 (1996) (plurality opinion). The Court contends that the
historical formulations of the insanity defense were so diverse, so
contested, as to make it impossible to discern a unified principle
that Kansas’ approach offends. I disagree.

															Few doctrines are as deeply rooted in our
common-law heritage as the insanity defense. Although English and
early American sources differ in their linguistic formulations of
the legal test for insanity, with striking consistency, they all
express the same underlying idea: A defendant who, due to mental
illness, lacks sufficient mental capacity to be held morally
responsible for his actions cannot be found guilty of a crime. This
principle remained embedded in the law even as social mores shifted
and medical understandings of mental illness evolved. Early
American courts incorporated it into their jurisprudence. The
States eventually codified it in their criminal laws. And to this
day, the overwhelming majority of U. S. jurisdictions
recognize insanity as an affirmative defense that excuses a
defendant from criminal liability even where he was capable of
forming the mens rea required for the offense. See Appendix, infra .

															A

															Consider the established common-law background
of the insanity defense at and around the time the Framers wrote
the Constitution. The four preeminent common-law jurists, Bracton,
Coke, Hale, and Blackstone, each linked criminality to the presence
of reason, free will, and moral understanding. It is “will and
purpose,” wrote Henry de Bracton in his 13th-century treatise, that
“mark maleficia [misdeeds].” 2 Bracton On Laws and Customs
of England 384 (S. Thorne transl. 1968) (Bracton); Oxford Latin
Dictionary 1067 (P. Glare ed. 1982). A “madman,” he explained, “can
no more commit an injuria [unlawful conduct] or a felony
than a brute animal, since they are not far removed from brutes.” 2
Bracton 424; Oxford Latin Dictionary, at 914. Seizing on Bracton’s
reference to “brute animals” (sometimes translated “wild beasts”),
the Court concludes that Bracton’s approach, like Kansas’, would
excuse only those who lack capacity to form any intention at all.
See ante , at 15. But what does it mean to be like a “brute
animal”? A brute animal may well and readily intend to commit a
violent act without being able to judge its moral nature. For
example, when a lion stalks and kills its prey, though it acts
intentionally, it does not offend against the criminal laws. See 2
Bracton 379 (noting that “murder” is defined as “by the hand of
man” to “distinguish it from the case of those slain or devoured by
beasts and animals which lack reason”).

															Bracton’s other references to “madmen” shed
further light on the meaning he attached to that term. Bracton
described such persons as “without sense and reason” and “lack[ing] animus .” Id. , at 324, 424. And he likened a “lunatic”
to an “infant,” who cannot be held liable in damages unless he “is
capable of perceiving the wrongful character of his act.” Id. , at 324; see also 4 id ., at 356 (“in many ways a
minor and a madman are considered equals or not very different,
because they lack reason” (footnote omitted)). Thus, Bracton’s
“brute animal” included those who lacked the qualities of reason
and judgment that make human beings responsible moral agents. See
Platt, The Origins and Development of the “Wild Beast” Concept of
Mental Illness and Its Relation to Theories of Criminal
Responsibility, 1 Issues in Crim. 1, 6 (1965).

															Leaving Bracton, let us turn to Sir Edward Coke,
writing in the early 17th century. Coke wrote that “the act and
wrong of a mad man shall not be imputed to him,” not because he
could not engage in intentional conduct (the equivalent of the
modern concept of mens rea ), but because he lacked something
more—“mind or discretion.” 2 Institutes of the Laws of England
§405, p. 247b (1628). Coke, like Bracton before him, likened a
“mad man” to an “[i]nfant,” who could not be punished as a criminal
“untill he be of the age of fourteene, which in Law is accounted
the age of discretion.” Ibid . What is it that the “[i]nfant”
lacks? Since long before Coke’s time, English jurists and scholars
believed that it was the moral nature, not the physical nature, of
an act that a young child is unlikely to understand. See Platt
& Diamond, The Origins of the “Right and Wrong” Test of
Criminal Responsibility and Its Subsequent Development in the
United States: An Historical Survey, 54 Cal. L. Rev. 1227,
1233–1234 (1966) (Platt & Diamond).

															Sir Matthew Hale also premised criminal
liability on the presence of “understanding and liberty of will,”
without which “there can be no transgression, or just reason to
incur the penalty or sanction that law instituted for the
punishment of the crimes or offenses.” 1 Pleas of the Crown, ch. 2,
pp. 14–15 (1736). Hale, too, likened insane persons to
“infants” under the age of 14, who were subject to the criminal
laws only if they “had discretion to judge between good and evil.” Id. , ch. 3, at 26–27; id. , ch. 4, at 30 (a person who
is “labouring under melancholy distempers hath yet ordinarily as
great understanding, as ordinarily a child of fourteen years hath,
is such a person as may be guilty of treason or felony”). Those
suffering from “total insanity” could not be guilty of capital
offenses, “for they have not the use of understanding, and act not
as reasonable creatures, but their actions are in effect in the
condition of brutes.” Id. , at 30–32.

															Sir William Blackstone, whose influence on the
founding generation was the most profound, was yet more explicit. A
criminal offense, he explained, requires both a “vitious will” and
a “vitious act.” 4 Commentaries on the Laws of England 21 (1769).
Persons suffering from a “deficiency in will” arising from a
“defective or vitiated understanding” were “not [criminally]
chargeable for their own acts.” Id. , at 24. Citing Coke, he
explained that murder must be “committed by a person of sound
memory and discretion” because a “lunatic or infant” is “incapable
of committing any crime, unless in such cases where they shew a
consciousness of doing wrong, and of course a discretion, or
discernment, between good and evil.” Id. , at 195–196. And he
opined that deprivation of “the capacity of discerning right from
wrong” is necessary “to form a legal excuse.” Id. , at
189.

															These four eminent jurists were not alone.
Numerous other commentators expressly linked criminal liability
with the accused’s capacity for moral agency. William Lambard’s
1581 treatise ranked a “mad man” as akin to a “childe” who had “no
knowledge of good nor evil.” Eirenarcha, ch. 21, p. 218. If
such a person killed a man, that is “no felonious acte” because
“they can[n]ot be said to have any understanding wil[l].” Ibid. But if “upon examination” it appeared that “they knew
what they did, [and] it was ill , the[n] seemeth it to be
otherwise.” Ibid. (emphasis added). Michael Dalton’s 1618
manual for justices of the peace instructed that “[i]f one that is Non compos mentis . . . kill a man, this is no
felonie; for they have no knowledge of good and evill, nor can have
a felonious intent, nor a will or mind to do harme.” The Countrey
Justice 215. William Hawkins, in 1716, wrote that “those who,” like
“[l]unaticks,” are “under a natural Disability of distinguishing
between Good and Evil . . . are not punishable by any
criminal Prosecution whatsoever.” 1 Pleas of the Crown §1,
p. 2; see also id. , at 1 (“The Guilt of offending
against any Law whatsoever . . . can never justly be
imputed to those who are either uncapable of understanding it, or
of conforming themselves to it”).

															English treatises on the law of mental
disability adopted the same view. George Collinson explained that
“[t]o excuse a man in the commission of a crime, he must at the
period when he committed the offense, have been wholly incapable of
distinguishing between good and evil, or of comprehending the
nature of what he is doing.” Treatise on the Law Concerning Idiots,
Lunatics, and Other Persons Non Compotes Mentis §7, p. 474
(1812) (Collinson); see also id. , §2, at 471 (“[A]n evil
intention is implied in every offence, and constitutes the charge
of every indictment: but a non compos, not having a will of his
own, cannot have an intention morally good or bad; so that the
overt act by which alone the motives of other men are discerned,
with respect to him proves nothing”). Similarly, Leonard Shelford,
summarizing English case law, wrote that “[t]he essence of a crime
consists in the animus or intention of the person who commits it,
considered as a free agent, and in a capacity of distinguishing
between moral good and evil.” Practical Treatise on the Law
Concerning Lunatics, Idiots, and Persons of Unsound Mind 458 (1833)
(emphasis deleted).

															The majority believes that I am
“cherry-pick[ing]” references to moral understanding while ignoring
references to intent and mens rea . See ante , at
15–17, nn. 8, 9. With respect, I disagree. The Court points
out, correctly, that many of the common-law sources state that the
insane lack mens rea or felonious intent. But what did they
mean by that? At common law, the term mens rea ordinarily
incorporated the notion of “general moral blameworthiness” required
for criminal punishment. Sayre, Mens Rea, 45 Harv. L. Rev. 974, 988
(1932); 3 Encyclopedia of Crime and Justice 995 (2d ed. 2002) (as
used at common law, the term mens rea “is synonymous with a
person’s blameworthiness”). The modern meaning of mens rea is narrower and more technical. Ibid. It refers to the
“state of mind or inattention that, together with its accompanying
conduct, the criminal law defines as an offense.” Ibid. When
common-law writers speak of intent or mens rea , we cannot
simply assume that they use those terms in the modern sense. That
is an anachronism. Instead, we must examine the context to
understand what meaning they ascribed to those terms. And when we
do so, we see that, over and over again, they link criminal intent
to the presence of free will and moral understanding. The Court
dismisses those passages as just “some ‘good and evil’ language.” Ante , at 17, n. 9. But it fails to explain why, if mens rea in the modern sense were sufficient, these
common-law writers discuss the role of moral agency at all, much
less why such language appears in virtually every treatise and
virtually every case. In the Court’s view, all that is just spilled
ink.

															The English case law illustrates this point. In
the seminal case of Rex v. Arnold , 16 How. St. Tr.
695 (1724), the defendant stood accused of shooting Lord Onslow
while laboring under the insane delusion that Onslow had bewitched
him. Id. , at 699, 721. The Court emphasizes Justice Tracy’s
statement to the jury that if a man is “ ‘deprived of his
reason, and consequently of his intention, he cannot be
guilty,’ ” concluding that the court adopted a modern mens
rea test. Ante , at 16. But in the passage immediately
preceding that statement, Justice Tracy explained that the
defendant’s intent to shoot was clearly proved, and that the only
remaining question was whether his mental illness excused him from
blame:

															“That he shot, and that wilfully [is
proved]: but whether maliciously, that is the thing: that is the
question; whether this man hath the use of his reason and sense? If
he was under the visitation of God, and could not distinguish
between good and evil, and did not know what he did, though he
committed the greatest offence, yet he could not be guilty of any
offence against any law whatsoever; for guilt arises from the mind,
and the wicked will and intention of the man. If a man be deprived of his reason, and consequently of his intention, he
cannot be guilty ; and if that be the case, though he had
actually killed my lord Onslow, he is exempted from punishment.” 16
How. St. Tr., at 764 (emphasis added; brackets in original).

															See also ibid. (summarizing the testimony
of one Mr. Coe, who testified that he went to the defendant three
days after the shooting “and asked him, If he intended to kill my
lord Onslow? and he said, Yes, to be sure”). On the next page,
Justice Tracy concluded that the jury must determine whether the
evidence “doth shew a man, who knew what he was doing, and was able
to distinguish whether he was doing good or evil, and understood
what he did.” Id. , at 765.

															Likewise, in the case of Rex v. Lord
Ferrers , 19 How. St. Tr. 886 (1760), the solicitor general
instructed the members of the House of Lords to consider the
“ ‘capacity and intention’ ” of the accused, to be sure, ante , at 17, but what did he mean by those terms? The
ultimate question of insanity, he explained, depended on the
defendant’s capacity at the time of the offense to distinguish
right from wrong:

															“My lords, the question therefore must be
asked; is the noble prisoner at the bar to be acquitted from the
guilt of murder, on account of insanity? It is not pretended to be
a constant general insanity. Was he under the power of it, at the
time of the offence committed? Could he, did he, at that time,
distinguish between good and evil?” 19 How. St. Tr., at 948.

															In summation, the solicitor general argued that
Lord Ferrers’ own witnesses failed to provide any testimony “which
proves his lunacy or insanity at any time.” Id. , at 952.
Reviewing the pertinent evidence, he noted that one witness
testified that he “had observed great oddities in my lord,” but
acknowledged that he “never saw him in such a situation, as not to
be capable of distinguishing between good and evil, and not to
know, that murder was a great crime.” Ibid. Another admitted
under questioning by the Lords that “he thought lord Ferrers
capable of distinguishing between moral and immoral actions.” Ibid. The defendant’s brother was the only witness to
testify that “at particular times, the noble lord might not be able
to distinguish between moral good and evil,” but even he, the
solicitor general argued, had been unable to testify to “any
instance within his own recollection.” Id. , at 953. If Lord
Ferrers’ bare intention to kill were sufficient to convict, why the
extensive discussion of the evidence concerning his capacity for
moral understanding?

															These examples reflect the prevailing view of
the law around the time of the founding. Judges regularly
instructed juries that the defendant’s criminal liability depended
on his capacity for moral responsibility. See, e.g. , Trial of Samuel Burt (July 19, 1786), in 6 Old Bailey
Proceedings 875 (E. Hodgson ed. 1788) (to acquit based on insanity,
it must be shown that the mental disorder “takes away from the
party all moral agency and accountability,” and “destroys in them,
for the time at least, all power of judging between right and
wrong”); Trial of Francis Parr (Jan. 15, 1787), 2 id. , at 228 (jury must “judge whether at the moment of
committing [the offense] he was not a moral agent, capable of
discerning between good and evil, and of knowing the consequences
of what he did”); Bowler’s Case , 1 Collinson 673–674, n.
(judge “concluded by observing to the jury, that it was for them to
determine whether the Prisoner, when he committed the offence with
which he stood charged, was or was not incapable of distinguishing
right from wrong”). The government’s attorneys agreed that this was
the proper inquiry. See, e.g. , Parker’s Case , 1 id. , at 479–480 (the Attorney General argued that “the jury
must be perfectly satisfied, that at the time when the crime was
committed, the prisoner did not really know right from wrong”).

															In none of the common-law cases was the judge’s
reference to the defendant’s capacity for moral agency simply a
proxy for the narrow modern notion of mens rea . See ante , at 17. Something more was required. Consider Bellingham’s Case , 1 Collinson 636. The defendant stood
accused of the murder of Spencer Perceval, the Chancellor of the
Exchequer, in the lobby of the House of Commons. Ibid. The
Court emphasizes Chief Justice Mansfield’s statement that one who
could not distinguish right from wrong “ ‘could have no
intention at all,’ ” concluding that Chief Justice Mansfield
viewed moral incapacity as a symptom of cognitive breakdown rather
than a test of insanity. Ante , at 18. But, as in Rex v. Arnold , see supra, at 9–10, the defendant’s
intention to shoot Perceval was not seriously in dispute. 1
Collinson 670. Instead, his guilt or innocence turned on his
capacity for moral blame. The “single question” for the jury,
charged the Chief Justice, “was whether, when [the defendant]
committed the offence charged upon him, he had sufficient
understanding to distinguish good from evil, right from wrong, and
that murder was a crime not only against the law of God, but
against the law of his Country.” Id ., at 673. Lord
Lyndhurst, presiding over the case of Rex v. Offord ,
5 Car. & P. 168, 172 Eng. Rep. 924 (N. P. 1831), certainly
understood that inquiry to be the crux of Chief Justice Mansfield’s
charge. Citing Bellingham’s Case , he instructed the jury
that “[t]he question was, did [the accused] know that he was
committing an offence against the laws of God and nature?” 5 Car.
& P., at 168, 172 Eng. Rep., at 925.

															The Court dismisses other common-law cases as
failing to articulate a clear legal standard. See ante , at
18–19. But these cases, too, required more than bare intent. In Hadfield’s Case , 27 How. St. Tr. 1281 (1800), the defendant
was acquitted after the prosecution conceded that he was “in a
deranged state of mind” when he shot at King George III. Id ., at 1353. And in Regina v. Oxford , 9 Car.
& P. 525, 173 Eng. Rep. 941 (N. P. 1840), the court observed
that a “person may commit a criminal act, and yet not be
responsible.” Id. , at 546, 173 Eng. Rep., at 950. Although
it acknowledged the difficulty of “lay[ing] down the rule of the
English law on the subject,” it summed up the inquiry as “whether
the prisoner was labouring under that species of insanity which
satisfies you that he was quite unaware of the nature, character,
and consequences of the act he was committing, or, in other words,
whether he was under the influence of a diseased mind, and was
really unconscious at the time he was committing the act, that it
was a crime.” Id. , at 546–547, 173 Eng. Rep., at 950.
Although these and other English cases discuss insanity in terms
that are less precise than our modern taxonomy of mental states,
their lesson is clear. To be guilty of a crime, the accused must
have something more than bare ability to form intentions and carry
them out.

															B

															These fundamental principles of criminal
responsibility were incorporated into American law from the early
days of the Republic. Early American commentaries on the criminal
law generally consisted of abridgments of the works of prominent
English jurists. As early as 1792, one such abridgment instructed
that “lunaticks, who are under a natural disability of
distinguishing between good and evil are not punishable by any
criminal prosecution.” R. Burn, Abridgment, or the American Justice
300; see also W. Stubbs, Crown Circuit Companion 288 (1 Am. ed.
1816) (“If one that is non compos mentis . . .
kill a man, this is no felony; for they have not knowledge of good
and evil, nor can have a felonious intent, nor a will or mind to do
harm”). And an influential founding-era legal dictionary described
the “general rule” that lunatics, “being by reason of their natural
disabilities incapable of judging between good and evil, are
punishable by no criminal prosecution whatsoever.” 2 T. Cunningham,
New and Complete Law Dictionary (2d corr. ed. 1771). Similarly, the
first comprehensive American text on forensic medicine, published
in 1823, cited Chief Justice Mansfield’s charge to the jury in Bellingham’s Case for the proposition that “[s]o long as
they could distinguish good from evil, so long would they be
answerable for their conduct.” 1 T. Beck, Elements of Medical
Jurisprudence 369. These principles, it concluded, “are doubtless
correct, and conducive to the ends of justice.” Id. , at
370.

															Early American jurists closely hewed to these
principles. In case after case, judges instructed juries that they
must inquire into the defendant’s capacity for moral understanding.
See, e.g. , Meriam’s Case , 7 Mass. 168 (1810), 6
N. Y. City-Hall Recorder 162 (1822) (whether the defendant was
“at the time, capable of distinguishing good from evil”); Clark’s Case , 1 N. Y. City-Hall Recorder 176, 177
(1816) (same); Ball’s Case , 2 N. Y. City-Hall Recorder
85, 86 (1817) (same); United States v. Clarke , 25 F.
Cas. 454 (No. 14,811) (CC DC 1818) (whether defendant was “in such
a state of mental insanity . . . as not to have been
conscious of the moral turpitude of the act”); Cornwell v. State , 8 Tenn. 147, 155 (1827) (whether the prisoner “had
not sufficient understanding to know right from wrong”).

															C

															As the foregoing demonstrates, by the time the
House of Lords articulated the M’Naghten test in 1843, its
“essential concept and phraseology” were “already ancient and
thoroughly embedded in the law.” Platt & Diamond 1258; see also
1 W. Russell, Crimes and Misdemeanors 8–14 (3d ed. 1843)
(summarizing the pre- M’Naghten English case law and
concluding that the key questions were whether “there be thought
and design, a faculty to distinguish the nature of actions, [and]
to discern the difference between moral good and evil”). Variations
on the M’Naghten rules soon became the predominant standard
in the existing states of the United States. Platt & Diamond
1257. That tradition has continued, almost without exception, to
the present day.

															It is true that, even following M’Naghten , States continued to experiment with different
formulations of the insanity defense. See ante , at 19–20.
Some adopted the volitional incapacity, or “irresistible-impulse,”
test. But those States understood that innovation to expand, not
contract, the scope of the insanity defense, excusing not only
defendants who met some variant of the traditional M’Naghten test but also those who understood that their conduct was wrong but
were incapable of restraint. See, e.g. , Parsons v. State , 81 Ala. 577, 584–585, 2 So. 854, 858–859 (1887); Bradley v. State , 31 Ind. 492, 507–508 (1869); State v. Felter , 25 Iowa 67, 82–83 (1868); Hopps v. People , 31 Ill. 385, 391–392 (1863).

															So too, the “offspring” or “product” test, which
asks whether the defendant’s conduct was attributable to mental
disease or defect. The States that adopted this test did so out of
the conviction that the M’Naghten test was too restrictive
in its approach to assessing the accused’s capacity for criminal
responsibility. See Durham v. United States , 214 F.2d
862, 874 (CADC 1954) (“We conclude that a broader test should be
adopted”); State v. Pike , 49 N. H. 399, 441–442
(1870); see also Reid, Understanding the New Hampshire Doctrine of
Criminal Insanity, 69 Yale L. J. 367, 386 (1960) (“[T]he New
Hampshire doctrine . . . is more liberal and has a wider
range than M’Naghten rules”). Even as States experimented
with broader insanity rules, they retained the core of the
traditional common-law defense.

															In the early 20th century, several States
attempted to break with that tradition. The high courts of those
States quickly struck down their restrictive laws. As one justice
of the Mississippi Supreme Court wrote in 1931: The “common law
proceeds upon an idea that before there can be a crime there must
be an intelligence capable of comprehending the act prohibited, and
the probable consequence of the act, and that the act is wrong.” Sinclair v. State , 161 Miss. 142, 158, 132 So. 581,
583 (Ethridge, J., concurring). Accordingly, Justice Ethridge said,
insanity “has always been a complete defense to all crimes from the
earliest ages of the common law.” Ibid. ; State v. Strasburg , 60 Wash. 106, 116, 110 P. 1020, 1022–1023 (1910);
cf. State v. Lange , 168 La. 958, 965, 123 So. 639,
642 (1929).

															Today, 45 States, the Federal Government, and
the District of Columbia continue to recognize an insanity defense
that retains some inquiry into the blameworthiness of the accused.
Seventeen States and the Federal Government use variants of the M’Naghten test, with its alternative cognitive and moral
incapacity prongs. Three States have adopted M’Naghten plus
the volitional test. Ten States recognize a defense based on moral
incapacity alone. Thirteen States and the District of Columbia have
adopted variants of the Model Penal Code test, which combines
volitional incapacity with an expanded version of moral incapacity.
See Appendix, infra . New Hampshire alone continues to use
the “product” test, asking whether “a mental disease or defect
caused the charged conduct.” State v. Fichera , 153
N. H. 588, 593, 903 A.2d 1030, 1035 (2006). This broad test
encompasses “ ‘whether the defendant knew the difference
between right and wrong and whether the defendant acted
impulsively,’ ” as well as “ ‘whether the defendant was
suffering from delusions or hallucinations.’ ” State v. Cegelis , 138 N. H. 249, 255, 638 A.2d 783, 786 (1994).
And North Dakota uses a unique formulation that asks whether the
defendant “lacks substantial capacity to comprehend the harmful
nature or consequences of the conduct, or the conduct is the result
of a loss or serious distortion of the individual’s capacity to
recognize reality.” N. D. Cent. Code Ann. §12.1–04.1–01(1)
(2012).

															Of the States that have adopted the M’Naghten or Model Penal Code tests, some interpret
knowledge of wrongfulness to refer to moral wrong, whereas others
hold that it means legal wrong. See ante , at 2–3,
20–22 . While there is, of course, a logical distinction
between those interpretations, there is no indication that it makes
a meaningful difference in practice. The two inquiries are closely
related and excuse roughly the same universe of defendants. See State v. Worlock , 117 N. J. 596, 609–611, 569 A.2d 1314 , 1321–1322 (1990) (“In most instances, legal
wrong is coextensive with moral wrong”); State v. Crenshaw , 98 Wash. 2d 789 , 799, 659 P.2d 488 , 494 (1983) (“ ‘[S]ince by far the vast majority
of cases in which insanity is pleaded as a defense to criminal
prosecutions involves acts which are universally recognized as
morally wicked as well as illegal, the hair-splitting distinction
between legal and moral wrong need not be given much attention’ ”); People v. Schmidt , 216 N.Y. 324, 340, 110 N.E. 945,
949 (1915) (Cardozo, J.) (“Knowledge that an act is forbidden by
law will in most cases permit the inference of knowledge that,
according to the accepted standards of mankind, it is also
condemned as an offense against good morals”); see also ALI, Model
Penal Code §4.01, Explanatory Note, p. 164 (1985) (explaining that
“few cases are likely to arise in which the variation will be
determinative”).

															III

															A

															Consider the basic reason that underlies and
explains this long legal tradition. That reason reveals that more
is at stake than its duration alone. The tradition reflects the
fact that a community’s moral code informs its criminal law. As
Henry Hart stated it, the very definition of crime is conduct that
merits “a formal and solemn pronouncement of the moral condemnation
of the community.” The Aims of the Criminal Law, 23 Law &
Contemp. Prob. 401, 405 (1958).

															The criminal law does not adopt, nor does it
perfectly track, moral law. It is no defense simply to claim that
one’s criminal conduct was morally right. But the criminal law
nonetheless tries in various ways to prevent the distance between
criminal law and morality from becoming too great. In the words of
Justice Holmes, a law that “punished conduct [that] would not be
blameworthy in the average member of the community would be too
severe for that community to bear.” O. Holmes, The Common Law 50
(1881); see also ibid. (“[T]o deny that criminal liability
. . . is founded on blameworthiness . . . would
shock the moral sense of any civilized community”).

															Sometimes the criminal law seeks to keep its
strictures roughly in line with the demands of morality through
grants of discretion that will help it to reach appropriate results
in individual cases, including special instances where the law
points one way and morality the other. Thus, prosecutors need not
prosecute. Jurors (however instructed) may decide to acquit. Judges
may exercise the discretion the law allows them to impose a lenient
sentence. Executives may grant clemency.

															And sometimes the law attempts to maintain this
balance by developing and retaining a “collection of interlocking
and overlapping concepts,” including defenses, that will help
“assess the moral accountability of an individual for his
antisocial deeds.” Powell v. Texas , 392 U.S.
514 , 535–536 (1968) (plurality opinion). These concepts and
defenses include “ actus reus , mens rea , insanity,
mistake, justification, and duress.” Id. , at 536.

															As we have recognized, the “process of
adjustment” within and among these overlapping legal concepts “has
always been thought to be the province of the States.” Ibid. Matters of degree, specific content, and aptness of application all
may be, and have always been, the subject of legal dispute. But the
general purpose—to ensure a rough congruence between the criminal
law and widely accepted moral sentiments—persists. To gravely
undermine the insanity defense is to pose a significant obstacle to
this basic objective.

															The majority responds that Kansas has not
removed the element of blameworthiness from its treatment of
insanity; it has simply made a different judgment about what
conduct is blameworthy. See ante , at 13,
n. 7 . That is not how the Kansas Supreme Court has
characterized its law. See State v. Bethel , 275 Kan.
456, 472, 66 P.3d 840, 850 (2003) (holding that Kansas law provides
for “no consideration,” at the guilt phase, “of whether
wrongfulness was inherent in the defendant’s intent”). In any
event, as the Court acknowledges, the States’ discretion in this
area must be constrained within “broad limits,” ante , at 7,
which are derived from history and tradition. The question is
whether Kansas’ approach transgresses those limits. I doubt that
the Court would declare, for example, that a State may do away with
the defenses of duress or self-defense on the ground that, in its
idiosyncratic judgment, they are not required. With respect to the
defense of insanity, I believe that our history shows clearly that
the criminal law has always required a higher degree of individual
culpability than the modern concept of mens rea . See Part
II, supra . And in my view, Kansas’ departure from this long
uniform tradition poses a serious problem.

															B

															To see why Kansas’ departure is so serious, go
back to our two simplified prosecutions: the first of the defendant
who, because of serious mental illness, believes the victim is a
dog; the second of a defendant who, because of serious mental
illness, believes the dog commanded him to kill the victim. Now
ask, what moral difference exists between the defendants in the two
examples? Assuming equivalently convincing evidence of mental
illness, I can find none at all. In both cases, the defendants
differ from ordinary persons in ways that would lead most of us to
say that they should not be held morally responsible for their
acts. I cannot find one defendant more responsible than the other.
And for centuries, neither has the law.

															More than that, scholars who have studied this
subject tell us that examples of the first kind are rare. See Brief
for 290 Criminal Law and Mental Health Law Professors as Amici
Curiae 12. Others repeat this claim. See Slobogin, An End to
Insanity: Recasting the Role of Mental Disability in Criminal
Cases, 86 Va. L. Rev. 1199, 1205 (2000); Morse, Mental Disorder and
Criminal Law, 101 J. Crim. L. & C. 885, 933 (2011). That is
because mental illness typically does not deprive individuals of
the ability to form intent. Rather, it affects their motivations for forming such intent. Brief for 290 Criminal
Law and Mental Health Law Professors as Amici Curiae 12. For
example, the American Psychiatric Association tells us that
individuals suffering from mental illness may experience
delusions—erroneous perceptions of the outside world held with
strong conviction. They may believe, incorrectly, that others are
threatening them harm (persecutory delusions), that God has
commanded them to engage in certain conduct (religious delusions),
or that they or others are condemned to a life of suffering
(depressive delusions). Brief for American Psychiatric Association
et al. as Amici Curiae 25–26. Such delusions may, in
some cases, lead the patient to behave violently. Id. , at
28. But they likely would not interfere with his or her perception
in such a way as to negate mens rea . See H. R. Rep. No.
98–577, p. 15 n. 23 (1984) (“Mental illness rarely, if ever,
renders a person incapable of understanding what he or she is
doing. Mental illness does not, for example, alter the perception
of shooting a person to that of shooting a tree.”).

															Kansas’ abolition of the second part of the M’Naghten test requires conviction of a broad swath of
defendants who are obviously insane and would be adjudged not
guilty under any traditional form of the defense. This result
offends deeply entrenched and widely recognized moral principles
underpinning our criminal laws. See, e.g. , National Comm’n
on Reform of Fed. Crim. Laws, Final Report, Proposed New Fed. Crim.
Code §503, pp. 40–41 (1971) (to attribute guilt to a
“manifestly psychotic person” would “be immoral and inconsistent
with the aim of a criminal code”); H. R. Rep. No. 98–577,
at 7–8 (“[T]he abolition of the affirmative insanity defense
would alter that fundamental basis of Anglo-American criminal law:
the existence of moral culpability as a prerequisite for
punishment”); ABA Criminal Justice Mental Health Standards §7–6.1,
pp. 336–338 (1989) (rejecting the mens rea approach
“out of hand” as “a jarring reversal of hundreds of years of moral
and legal history” that “inhibits if not prevents the exercise of
humane judgment that has distinguished our criminal law
heritage”).

															By contrast, the rule adopted by some States
that a defendant must be acquitted if he was unable to appreciate
the legal wrongfulness of his acts, see ante ,
at 20–22, would likely lead to acquittal in the mine run of
such cases. See supra, at 17. If that is so, then that rule
would not pose the same due process problem as Kansas’ approach.
That issue is not before us, as Kansas’ law does not provide even
that protection to mentally ill defendants.

															C

															Kansas and the Solicitor General, in their
efforts to justify Kansas’ change, make four important arguments.
First, they point to cases in this Court in which we have said that
the States have broad leeway in shaping the insanity defense. See Leland , 343 U.S.
790 ; Clark , 548 U.S.
735 . In Leland , we rejected the defendant’s argument
that the Constitution required the adoption of the
“ ‘irresistible impulse’ ” test. 343 U. S., at
800–801. Similarly, in Clark , we upheld Arizona’s effort to
eliminate the first part of the M’Naghten rule, applicable
to defendants whose mental illness deprived them of the ability to
know the “ ‘nature and quality of the act,’ ” 548
U. S., at 747–748. If Arizona can eliminate the first prong of M’Naghten , Kansas asks, why can Kansas not eliminate the
second part?

															The answer to this question lies in the fact
that Arizona, while amending the insanity provisions of its
criminal code, did not in practice eliminate the traditional
insanity defense in any significant part. See 548 U. S., at
752, n. 20 (reserving the question whether “the Constitution
mandates an insanity defense”). As we pointed out, “cognitive
incapacity is itself enough to demonstrate moral incapacity.” Id. , at 753. Evidence that the defendant did not know what
he was doing would also tend to establish that he did not know that
it was wrong. Id. , at 753–754. And Prosecution One (he
thought the victim was a dog) would still fail. The ability of the
States to refuse to adopt other insanity tests, such as the
“irresistible impulse” test or the “product of mental illness” test
are also beside the point. See Leland , 343 U. S., at
800–801. Those tests both expand upon M’Naghten ’s
principles. Their elimination would cut the defense back to what it
traditionally has been, not, as here, eliminate its very
essence.

															Second, the United States as amicus
curiae suggests that the insanity defense is simply too
difficult for juries to administer. Brief for United States as Amicus Curiae 12–13. Without doubt, assessing the
defendant’s claim of insanity is difficult. That is one reason I
believe that States must remain free to refine and redefine their
insanity rules within broad bounds. But juries have been making
that determination for centuries and continue to do so in 45
States. And I do not see how an administrative difficulty can
justify abolishing the heart of the defense.

															Third, Kansas argues that it has not abolished
the insanity defense or any significant part of it. It has simply
moved the stage at which a defendant can present the full range of
mental-capacity evidence to sentencing. See Brief for Respondent 8; ante , at 4–5. But our tradition demands that an insane
defendant should not be found guilty in the first place. Moreover,
the relief that Kansas offers, in the form of sentencing discretion
and the possibility of commitment in lieu of incarceration, is a
matter of judicial discretion, not of right. See State v. Maestas , 298 Kan. 765, 316 P.3d 724 (2014). The insane
defendant is, under Kansas law, exposed to harsh criminal sanctions
up to and including death. And Kansas’ sentencing provisions do
nothing to alleviate the stigma and the collateral consequences of
a criminal conviction.

															Finally, Kansas argues that the insane, provided
they are capable of intentional action, are culpable and should be
held liable for their antisocial conduct. Brief for Respondent 40.
To say this, however, is simply to restate the conclusion for which
Kansas argues in this case. It is a conclusion that in my view runs
contrary to a legal tradition that embodies a fundamental precept
of our criminal law and that stretches back, at least, to the
origins of our Nation.

															For these reasons, with respect, I dissent.

															APPENDIX

															M’Naghten M’Naghten plus volitional incapacity

															Moral incapacity

															Model Penal Code

															Unique formulation

Summary:
The Supreme Court case of Kahler v. Kansas (2020) concerned the constitutionality of Kansas's treatment of a criminal defendant's insanity claim. The defendant, James Kahler, argued that his mental illness prevented him from understanding the wrongfulness of his actions when he committed murder.

Kansas, unlike many other states, does not recognize the "moral incapacity" test for insanity, which would exonerate a defendant who, due to mental illness, could not distinguish between right and wrong at the time of the crime. Instead, Kansas allows defendants to present evidence of mental illness during sentencing to seek a reduced sentence or commitment to a mental health facility.

The Court, in an opinion delivered by Justice Kagan, held that the Due Process Clause of the Constitution does not require states to adopt the moral incapacity test for insanity. The Court found that while the insanity defense has a long history in common law, it is not a fundamental principle that applies to the states via the Due Process Clause.

Justice Breyer dissented, arguing that the moral incapacity test is a fundamental aspect of the insanity defense and that its elimination in Kansas violates due process. He highlighted the role of the insanity defense in ensuring that only morally culpable individuals are subject to criminal punishment.

The Court's decision affirmed Kansas's approach to insanity defenses, allowing states flexibility in defining the standards for criminal culpability in cases involving mental illness.