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															SUPREME COURT OF THE UNITED STATES

															_________________

															No. 20–440

															_________________

															MINERVA SURGICAL, INC., PETITIONER v. HOLOGIC, INC., et al.

															on writ of certiorari to the united states
court of appeals for the federal circuit

															[June 29, 2021]

															Justice Kagan delivered the opinion of the
Court.

															In Westinghouse Elec. & Mfg. Co. v. Formica Insulation Co. , 266 U.S.
342 , 349 (1924), this Court approved the “well settled”
patent-law doctrine of “assignor estoppel.” That doctrine, rooted
in an idea of fair dealing, limits an inventor’s ability to assign
a patent to another for value and later contend in litigation that
the patent is invalid. The question presented here is whether to
discard this century-old form of estoppel. Continuing to see value
in the doctrine, we decline to do so. But in upholding assignor
estoppel, we clarify that it reaches only so far as the equitable
principle long understood to lie at its core. The doctrine applies
when, but only when, the assignor’s claim of invalidity contradicts
explicit or implicit representations he made in assigning the
patent.

															I

															Inventors look to the patent system to obtain
valuable rights. A typical patent application, filed with the U. S.
Patent and Trademark Office (PTO), includes a written description
and drawing of the invention and one or more claims particularly
setting out the invention’s scope. See 35 U. S. C.
§§111–113. The application also usually contains an inventor’s
oath—a statement attesting that the applicant is “the original
inventor” of the “claimed invention,” so that he is entitled to the
patent sought. §115. If the PTO decides that the invention meets
the “conditions for patentability”—mainly, that the invention is
useful, novel, and non-obvious—it will issue a patent to the
inventor. See §§101–103. That award gives the inventor the right to
exclude others from making, using, or selling the invention until
the patent expires (currently, 20 years after the application
date). See §154.

															The invention sparking this lawsuit is a device
to treat abnormal uterine bleeding, a medical condition affecting
many millions of women. Csaba Truckai, a founder of the company
Novacept, Inc., invented the device—called the NovaSure System—in
the late 1990s. He soon afterward filed a patent application, and
assigned his interest in the application—as well as in any future
“continuation applications”—to Novacept.[ 1 ] The NovaSure System, as described in Truckai’s
patent application, uses an applicator head to destroy targeted
cells in the uterine lining. To avoid unintended burning or
ablation (tissue removal), the head is “moisture permeable,”
meaning that it conducts fluid out of the uterine cavity during
treatment. The PTO issued a patent, and in 2001 the Food and Drug
Administration (FDA) approved the device for commercial
distribution. But neither Truckai nor Novacept currently benefits
from the NovaSure System patent. In 2004, Novacept sold its assets,
including its portfolio of patents and patent applications, to
another company (netting Truckai individually about $8 million).
And in another sale, in 2007, respondent Hologic, Inc. acquired all
patent rights in the NovaSure System. Today, Hologic sells that
device throughout the United States.

															Not through with inventing, Truckai founded in
2008 petitioner Minerva Surgical, Inc. There, he developed a
supposedly improved device to treat abnormal uterine bleeding.
Called the Minerva Endometrial Ablation System, the device (like
the NovaSure System) uses an applicator head to remove cells in the
uterine lining. But the new device, relying on a different way to
avoid unwanted ablation, is “moisture impermeable”: It does not
remove any fluid during treatment. The PTO issued a patent for the
device, and in 2015 the FDA approved it for commercial sale.

															Meanwhile, in 2013, Hologic filed a continuation
application requesting to add claims to its patent for the NovaSure
System. Aware of Truckai’s activities, Hologic drafted one of those
claims to encompass applicator heads generally, without regard to
whether they are moisture permeable. The PTO in 2015 issued the
altered patent as requested.

															A few months later, Hologic sued Minerva for
patent infringement. Minerva rejoined that its device does not
infringe. But more relevant here, it also asserted that Hologic’s
amended patent is invalid. The essential problem, according to
Minerva, is that the new, broad claim about applicator heads does
not match the invention’s description, which addresses their
water-permeability. See Defendant Minerva’s Opening Brief in
Support of Its Motion for Partial Summary Judgment in No.
15–cv–1031 (Del.), Doc. 300, pp. 8–9, 13–15; see also Festo
Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. , 535 U.S.
722 , 736 (2002) (“What is claimed by the patent application
must be the same” as what is described). In response, Hologic
invoked the doctrine of assignor estoppel. Because Truckai assigned
the original patent application, Hologic argued, he and Minerva
(essentially, his alter-ego) could not impeach the patent’s
validity. The District Court agreed that assignor estoppel barred
Minerva’s invalidity defense, and also ruled that Minerva had
infringed Hologic’s patent. See 325 F. Supp. 3d 507, 524–525,
532 (Del. 2018). At a trial on damages, a jury awarded Hologic
about $5 million.

															The Court of Appeals for the Federal Circuit
mainly upheld the judgment, focusing on assignor estoppel. The
court first “decline[d] Minerva’s invitation to ‘abandon [that]
doctrine.’ ” 957 F.3d 1256, 1267 (2020). Citing both this
Court’s precedents and equitable principles, the court affirmed the
doctrine’s “continued vitality.” Id., at 1268. An assignor,
the court stated, “should not be permitted to sell something and
later to assert that what was sold is worthless, all to the
detriment of the assignee.” Id. , at 1265. The assignor makes
an “implicit representation” that the rights “he is assigning
(presumably for value) are not worthless.” Ibid. It would
“work an injustice,” the court reasoned, to “allow the assignor to
make that representation at the time of assignment (to his
advantage) and later to repudiate it (again to his advantage).” Ibid. (quoting Diamond Scientific Co. v. Ambico,
Inc. , 848 F.2d 1220, 1224 (CA Fed. 1988)). The court then
applied assignor estoppel to bar Truckai and Minerva from raising
an invalidity defense. Here, the court rejected Minerva’s argument
that because “Hologic broadened the claims” after “Truckai’s
assignment,” it would “be unfair to block Truckai (or Minerva) from
challenging the breadth of those claims.” 957 F. 3d, at 1268.
Relying on circuit precedent, the court deemed it “irrelevant that,
at the time of the assignment, the inventor’s patent
application[ ] w[as] still pending” and that the assignee “may
have later amended the claims” without the inventor’s input. Ibid. (quoting Diamond Scientific , 848 F. 2d, at
1226).

															We granted certiorari, 592 U. S. ___
(2021), to consider the important issues raised in the Federal
Circuit’s judgment. Assignor estoppel, we now hold, is well
grounded in centuries-old fairness principles, and the Federal
Circuit was right to uphold it. But the court failed to recognize
the doctrine’s proper limits. The equitable basis of assignor
estoppel defines its scope: The doctrine applies only when an
inventor says one thing (explicitly or implicitly) in assigning a
patent and the opposite in litigating against the patent’s
owner.

															II

															Courts have long applied the doctrine of
assignor estoppel to deal with inconsistent representations about a
patent’s validity. The classic case (different in certain respects
from the one here) begins with an inventor who both applies for and
obtains a patent, then assigns it to a company for value. Later,
the inventor/assignor joins a competitor business, where he
develops a similar—and possibly infringing—product. When the
assignee company sues for infringement, the assignor tries to
argue—contrary to the (explicit or implicit) assurance given in
assigning the patent—that the invention was never patentable, so
the patent was never valid. That kind of about-face is what
assignor estoppel operates to prevent—or, in legalese, estop. As
one of the early American courts to use the doctrine held: The
assignor is not “at liberty to urge [invalidity] in a suit upon his
own patent against a party who derives title to that patent through
him.” Woodward v. Boston Lasting Mach. Co. , 60 F.
283, 284 (CA1 1894). Or as the Federal Circuit held in modern
times: The assignor’s explicit or “implicit representation” that
the patent he is assigning is “not worth- less . . .
deprive[s] him of the ability to challenge later the [patent’s]
validity.” Diamond Scientific , 848 F. 2d, at 1224.

															Assignor estoppel got its start in late
18th-century England and crossed the Atlantic about a hundred years
later. In the first recorded case, Lord Kenyon found that a patent
assignor “was by his own oath and deed estopped” in an infringement
suit from “attempt[ing] to deny his having had any title to
convey.” Oldham v. Langmead (1789), as described in
J. Davies, Collection of the Most Important Cases Respecting
Patents of Invention and the Rights of Patentees 442 (1816); see Hayne v. Maltby , 3 T. R. 439, 441, 100 Eng. Rep. 665,
666 (K. B. 1789) (recognizing the Oldham holding). That rule
took inspiration from an earlier doctrine—estoppel by deed—applied
in real property law to prevent a conveyor of land from later
asserting that he had lacked good title at the time of sale. See 2
E. Coke, The First Part of the Institutes of Laws of England 352a
(Hargrave & Butler eds., 19th ed. 1832) (1628). Lord Kenyon’s
new patent formulation of the doctrine grew in favor throughout the
1800s as an aspect of fair dealing: When “the Defendant sold and
assigned th[e] patent to the Plaintiffs as a valid one,” it “does
not lie in his mouth to say that the patent is not good.” Chambers v. Crichley , 33 Beav. 374, 376, 55 Eng. Rep.
412 (1864); see Walton v. Lavater , 8 C. B. N. S.
162, 187, 141 Eng. Rep. 1127, 1137 (C. P. 1860) (“The defendant,
who has received a large sum for the sale of this patent, ought not
to be allowed to raise any question as to its validity”). The
earliest American decision applying the doctrine dates from 1880.
See Faulks v. Kamp , 3 F. 898 (CC SDNY). Within a
decade or two, the doctrine was “so well established and generally
accepted that citation of authority is useless.” Griffith v. Shaw , 89 F. 313, 315 (CC SD Iowa 1893); see 2 W. Robinson,
Law of Patents for Useful Inventions §787 (1890) (collecting
cases).

															This Court first considered—and unanimously
approved—assignor estoppel in 1924, in Westinghouse v. Formica . Speaking through Chief Justice Taft, the Court
initially invoked the doctrine’s uniform acceptance in the lower
courts. The first decision applying assignor estoppel, the Court
recounted, was soon “followed by a myriad.” 266 U. S., at 349.
“[L]ater cases in nearly all the Circuit Courts of Appeal” were “to
the same point” as the first, adding up to a full “forty-five years
of judicial consideration and conclusion.” Ibid. Such a
“well settled” rule, in the Court’s view, should “not [be] lightly
disturb[ed].” Ibid. And so it was not disturbed, lightly or
otherwise. Rather, the Court added its own voice to that
pre-existing “myriad.” We announced that an assignor “is estopped
to attack” the “validity of a patented invention which he has
assigned.” Ibid. “As to the rest of the world,” the Court
explained, “the patent may have no efficacy”; but “the assignor can
not be heard to question” the assignee’s rights in what was
conveyed. Ibid. Westinghouse , like its precursor
decisions, grounded assignor estoppel in a principle of fairness.
“If one lawfully conveys to another a patented right,” the Court
reasoned, “fair dealing should prevent him from derogating from the
title he has assigned.” Id., at 350. After all, the “grantor
purports to convey the right to exclude others”; how can he later
say, given that representation, that the grantee in fact possesses
no such right? Ibid. The Court supported that view of equity
by referring to estoppel by deed. See supra, at 6. Under
that doctrine, the Court explained, “a grantor of a deed of land”
cannot “impeach[ ] the effect of his solemn act” by later
claiming that the grantee’s title is no good. Westinghouse ,
266 U. S., at 350. “The analogy” was “clear”: There was “no
reason why the principles of estoppel by deed should not apply to
[the] assignment of a patent right.” Id., at 348, 350. In
the latter context too, the Court held, the assignor could not
fairly “attack” the validity of a right he had formerly sold. Id., at 349.

															After thus endorsing assignor estoppel, the
Court made clear that the doctrine has limits. Although the
assignor cannot assert in an infringement suit that the patent is
invalid, the Court held that he can argue about how to construe the
patent’s claims. Here, the Court addressed the role in patent suits
of prior art—the set of earlier inventions (and other information)
used to decide whether the specified invention is novel and
non-obvious enough to merit a patent. Id., at 350. “Of
course,” the Court said, the assignor cannot use prior art in an
infringement suit “to destroy the patent,” because he “is estopped
to do this.” Id., at 351. But he can use prior art to
support a narrow claim construction—to “construe and narrow the
claims of the patent, conceding their validity.” Id., at
350–351. “Otherwise,” the Court explained, a judge “would be
denied” the “most satisfactory means” of “reaching a just
conclusion” about the patent’s scope—a conclusion needed to resolve
the infringement charge. Id., at 350–351. “The distinction”
thus established, the Court thought, “may be a nice one, but seems
to be workable.” Id., at 351. And, indeed, the Court applied
it to decide the case at hand for the assignor, finding that he had
not infringed the properly narrowed claim.[ 2 ]

															Finally, the Court left for another day several
other questions about the contours of assignor estoppel. One
concerned privity: When was an assignor so closely affiliated with
another party that the latter would also be estopped? See id., at 355. Another related to consideration: What if an
assignor had received only a nominal amount of money for
transferring the patent? See ibid. But the question that
most interested the Court was whether estoppel should operate
differently if the assignment was not of a granted patent but of a
patent application—as in fact was true in that case. The Court saw
a possible distinction between the two. In a patent application,
the Court began, the inventor “swor[e] to” a particular
“specification.” Id., at 352. But the exact rights at issue
were at that point “inchoate”—not “certainly defined.” Ibid. And afterward, the Court (presciently) observed, the claims might
be “enlarge[d]” at “the instance of the assignee” beyond what the
inventor had put forward. Id., at 353. That might weaken the
case for estoppel. But the Court decided not to decide the issue,
given its holding that the assignor had not infringed the
(narrowed) patent claim anyway.

															III

															Minerva’s main argument here, as in the
Federal Circuit, is that “assignor estoppel should be
eliminated”—and indeed has been already. Brief for Petitioner 17.
We reject that view. The doctrine has lasted for many years, and we
continue to accept the fairness principle at its core. Minerva’s
back-up contention is that assignor estoppel “should be
constrained.” Id., at 41. On that score, we find that the
Federal Circuit has applied the doctrine too expansively. Today, we
clarify the scope of assignor estoppel, including in the way Westinghouse suggested.

															A

															In its quest to abolish assignor estoppel,
Minerva lodges three main arguments. The first two offer different
reasons for why the doctrine is already defunct: because Congress
repudiated it in the Patent Act of 1952 and because, even if not,
this Court’s post- Westinghouse cases “leave no room for the
doctrine to continue.” Brief for Petitioner 20. The third, by
contrast, is a present-day policy claim: that assignor estoppel
“imposes” too high a “barrier to invalidity challenges” and so
keeps bad patents alive. Id., at 38. (The principal dissent
essentially endorses the first two arguments, but not the third.
See post, at 1, 4–6, 11 (opinion of Barrett, J.).)

															On the first point, we do not agree that the
Patent Act of 1952 abrogated assignor estoppel. The statutory
language Minerva relies on provides that “[i]nvalidity” of the
patent “shall be [a] defense[ ] in any action involving”
infringement. 35 U. S. C. §282(b). According to Minerva,
that language “instructs that invalidity must be available
as a defense in every [infringement] action,” thus
“leav[ing] no room for assignor estoppel.” Brief for Petitioner
17–18 (emphasis in original). But to begin with, similar language,
entitling a defendant to plead invalidity in any infringement
action, was in the patent statute when Westinghouse was
decided. See Patent Act of 1897, ch. 391, §2, 29Stat. 692 (“In any
action for infringement the defendant may plead” invalidity). And
anyway, Minerva’s view is untenable because it would foreclose
applying in patent cases a whole host of common-law preclusion
doctrines—not just assignor estoppel, but equitable estoppel,
collateral estoppel, res judicata, and law of the case. That broad
result would conflict with this Court’s precedents. See, e.g. , SCA Hygiene Products Aktiebolag v. First
Quality Baby Products, LLC , 580 U. S. ___, ___ (2017)
(slip op., at 16) (recognizing equitable estoppel in a patent
suit). And it would subvert congressional design. For Congress
“legislate[s] against a background of common-law adjudicatory
principles,” and it “expect[s]” those principles to “apply except
when a statutory purpose to the contrary is evident.” Astoria
Fed. Sav. & Loan Assn. v. Solimino , 501 U.S.
104 , 108 (1991) (internal quotation marks omitted). Assignor
estoppel was by 1952 just such a background principle of patent
adjudication, and Congress gave no indication of wanting to
terminate it or disturb its development. Nor has Congress done so
since that time.

															We likewise do not accept Minerva’s view that
two of our post- Westinghouse decisions have already interred
assignor estoppel. According to Minerva (quoting the case’s
dissent), Scott Paper Co. v. Marcalus Mfg. Co. “eliminated any justification for assignor estoppel and
‘repudiated’ the doctrine.” Reply Brief 13 (quoting 326 U.S.
249 , 264 (1945) (Frankfurter, J., dissenting)). And if that
were not enough, Minerva continues, our decision in Lear,
Inc. v. Adkins , 395 U.S.
653 (1969), also “eviscerated any basis for assignor estoppel.”
Reply Brief 13. But we think the words “eliminated,” “repudiated,”
and “eviscerated” are far off. Scott Paper and Lear in fact retained assignor estoppel; all they did was police the
doctrine’s boundaries (just as Westinghouse did and we do
today).

															Whatever a worked-up dissent charged, Scott
Paper did nothing more than decline to apply assignor estoppel
in a novel and extreme circumstance. The petitioner in Scott
Paper made the same ask Minerva does here: to abolish the Westinghouse rule. The Court expressly declined that
request. See 326 U. S., at 254. And it restated the “basic
principle” animating assignor estoppel, describing it as “one of
good faith, that one who has sold his invention may not, to the
detriment of the purchaser, deny the existence of that which he has
sold.” Id., at 251. The Court, to be sure, declined to apply
the doctrine in the case before it. There, estoppel would have
prevented the assignor from making a device on which the patent had
expired—a device, in other words, that had already entered the
public domain. The Court could not find any precedent for applying
estoppel in that situation. See id., at 254. And the Court
thought that doing so would carry the doctrine too far, reasoning
that the public’s interest in using an already-public invention
outweighs the “interest in private good faith.” Id., at
256–257. But the Court did not question—again, it reaffirmed—the
principle of fairness on which assignor estoppel rests in more
common cases, where the assignee is not claiming to control a
device unequivocally part of the public domain. See id., at
251. In those cases, the doctrine remained intact. Lear gives Minerva still less to work
with. In that case, the Court considered and toppled a different
patent estoppel doctrine. Called licensee estoppel, it barred (as
its name suggests) a patent licensee from contesting the validity
of the patent on a device he was paying to use. Minerva’s basic
claim is that as goes one patent estoppel rule, so goes another.
Brief for Petitioner 23–25. But Lear did not purport to
decide the fate of the separate assignor estoppel doctrine. To the
contrary, the Court stated that the patent holder’s “equities” in
the assignment context “were far more compelling than those
presented in the typical licensing arrangement.” 395 U. S., at
664. And so they are. As explained earlier, assignor estoppel rests
on the idea that the assignor has made an explicit or implicit
representation about the patent’s validity, and received some kind
of payment in return. See supra, at 5–6. No rationale of
that kind supports licensee estoppel. The licensee is a buyer of
patent rights, not a seller. He has given no assurances of the
patent’s worth. All he has done is purchase the right to use a
patented device—which, if the patent is invalid, he need not have
done. Lear ’s refusal to bar a licensee’s claim of invalidity
showed that the Court was alert to “the important public interest
in permitting full and free competition in the use of ideas”—and so
would not always apply patent estoppel doctrines. 395 U. S.,
at 670. But that does not mean, at the other extreme, always
rejecting those doctrines. Lear counseled careful attention
to the equities at stake in discrete patent contexts—and expressly
distinguished assignor from licensee estoppel.

															In sum, Scott Paper and Lear left Westinghouse right about where they found it—as a bounded
doctrine designed to prevent an inventor from first selling a
patent and then contending that the thing sold is worthless. Westinghouse saw that about-face as unfair; Scott
Paper and Lear never questioned that view. At the same
time, Westinghouse realized that assignor estoppel has
limits: Even in approving the doctrine, the Court made clear that
not every assignor defense in every case would fall within its
scope. See supra, at 7–8. Scott Paper and Lear adopted a similar stance. They maintained assignor estoppel, but
suggested (if in different ways) that the doctrine needed to stay
attached to its equitable moorings. The three decisions together
thus show not the doctrinal “eviscerat[ion]” Minerva claims, Reply
Brief 13, but only the kind of doctrinal evolution typical of
common-law rules.

															Finally, we do not think, as Minerva claims,
that contemporary patent policy—specifically, the need to weed out
bad patents—supports overthrowing assignor estoppel. In rejecting
that argument, we need not rely on stare decisis : “[C]orrect
judgments have no need for that principle to prop them up.” Kimble v. Marvel Entertainment, LLC , 576 U.S. 446,
455 (2015). And we continue to think the core of assignor estoppel
justified on the fairness grounds that courts applying the doctrine
have always given. Assignor estoppel, like many estoppel rules,
reflects a demand for consistency in dealing with others. See H.
Herman, The Law of Estoppel §3 (1871) (“An estoppel is an
obstruction or bar to one’s alleging or denying a fact contrary to
his own previous action, allegation or denial”). When a person
sells his patent rights, he makes an (at least) implicit
representation to the buyer that the patent at issue is valid—that
it will actually give the buyer his sought-for monopoly.[ 3 ] In later raising an invalidity
defense, the assignor disavows that implied warranty. And he does
so in service of regaining access to the invention he has just
sold. As the Federal Circuit put the point, the assignor wants to
make a “representation at the time of assignment (to his advantage)
and later to repudiate it (again to his advantage).” Diamond
Scientific , 848 F. 2d, at 1224; see supra, at 4. By
saying one thing and then saying another, the assignor wants to
profit doubly—by gaining both the price of assigning the patent and
the continued right to use the invention it covers. That course of
conduct by the assignor strikes us, as it has struck courts for
many a year, as unfair dealing—enough to outweigh any loss to the
public from leaving an invalidity defense to someone other than the
assignor.[ 4 ]

															B

															Still, our endorsement of assignor estoppel
comes with limits—true to the doctrine’s reason for being. Just as
we guarded the doctrine’s boundaries in the past, see supra, at 7–8, 11–13, so too we do so today. Assignor estoppel should
apply only when its underlying principle of fair dealing comes into
play. That principle, as explained above, demands consistency in
representations about a patent’s validity: What creates the
unfairness is contradiction. When an assignor warrants that a
patent is valid, his later denial of validity breaches norms of
equitable dealing. And the original warranty need not be express;
as we have explained, the assignment of specific patent claims
carries with it an implied assurance. See supra, at 13. But
when the assignor has made neither explicit nor implicit
representations in conflict with an invalidity defense, then there
is no unfairness in its assertion. And so there is no ground for
applying assignor estoppel.

															One example of non-contradiction is when the
assignment occurs before an inventor can possibly make a warranty
of validity as to specific patent claims. Consider a common
employment arrangement. An employee assigns to his employer patent
rights in any future inventions he develops during his employment;
the employer then decides which, if any, of those inventions to
patent. In that scenario, the assignment contains no representation
that a patent is valid. How could it? The invention itself has not
come into being. See Lemley, Rethinking Assignor Estoppel, 54
Houston L. Rev. 513, 525–527 (2016). And so the employee’s
transfer of rights cannot estop him from alleging a patent’s
invalidity in later litigation.

															A second example is when a later legal
development renders irrelevant the warranty given at the time of
assignment. Suppose an inventor conveys a patent for value, with
the warranty of validity that act implies. But the governing law
then changes, so that previously valid patents become invalid. The
inventor may claim that the patent is invalid in light of that
change in law without contradicting his earlier representation.
What was valid before is invalid today, and no principle of
consistency prevents the assignor from saying so.

															Most relevant here, another post-assignment
development—a change in patent claims—can remove the rationale for
applying assignor estoppel. Westinghouse itself anticipated
this point, which arises most often when an inventor assigns a
patent application, rather than an issued patent. As Westinghouse noted, “the scope of the right conveyed in such
an assignment” is “inchoate”—“less certainly defined than that of a
granted patent.” 266 U. S., at 352–353; see supra, at
9. That is because the assignee, once he is the owner of the
application, may return to the PTO to “enlarge[ ]” the
patent’s claims. 266 U. S., at 353; see 35 U. S. C.
§120; 37 CFR §1.53(b). And the new claims resulting from that
process may go beyond what “the assignor intended” to claim as
patentable. 266 U. S., at 353. Westinghouse did not
need to resolve the effects of such a change, but its liberally
dropped hints—and the equitable basis for assignor estoppel—point
all in one direction. Assuming that the new claims are materially
broader than the old claims, the assignor did not warrant to the
new claims’ validity. And if he made no such representation, then
he can challenge the new claims in litigation: Because there is no
inconsistency in his positions, there is no estoppel. The limits of
the assignor’s estoppel go only so far as, and not beyond, what he
represented in assigning the patent application.

															The Federal Circuit, in both its opinion below
and prior decisions, has failed to recognize those boundaries.
Minerva (recall, Truckai’s alter-ego) argued to the court that
estoppel should not apply because it was challenging a claim that
was materially broader than the ones Truckai had assigned. But the
court declined to consider that alleged disparity. Citing circuit
precedent, the court held it “irrelevant” whether Hologic had
expanded the assigned claims: Even if so, Minerva could not contest
the new claim’s validity. 957 F. 3d, at 1268 (quoting Diamond Scientific , 848 F. 2d, at 1226); see supra , at 4. For the reasons given above, that conclusion is
wrong. If Hologic’s new claim is materially broader than the ones
Truckai assigned, then Truckai could not have warranted its
validity in making the assignment. And without such a prior
inconsistent representation, there is no basis for estoppel.

															We remand this case to the Federal Circuit to
now address what it thought irrelevant: whether Hologic’s new claim
is materially broader than the ones Truckai assigned. The parties
vigorously disagree about that issue. In Truckai’s view, the new
claim expanded on the old by covering non-moisture-permeable
applicator heads. In Hologic’s view, the claim matched a prior one
that Truckai had assigned. Resolution of that issue in light of all
relevant evidence will determine whether Truckai’s representations
in making the assignment conflict with his later invalidity
defense—and so will determine whether assignor estoppel
applies.

															IV

															This Court recognized assignor estoppel a
century ago, and we reaffirm that judgment today. But as the Court
recognized from the beginning, the doctrine is not limitless. Its
boundaries reflect its equitable basis: to prevent an assignor from
warranting one thing and later alleging another. Assignor estoppel
applies when an invalidity defense in an infringement suit
conflicts with an explicit or implicit representation made in
assigning patent rights. But absent that kind of inconsistency, an
invalidity defense raises no concern of fair dealing—so assignor
estoppel has no place.

															For these reasons, we vacate the judgment of the
Federal Circuit and remand the case for further proceedings
consistent with this opinion.

															It is so ordered. Notes 1 A continuation
application enables an inventor to add to or modify the claims set
out in his original application. See 35 U. S. C. §120;
Manual of Patent Examining Procedure §201.07 (9th ed., June 2020).
But the continuation application may not materially change the
written description of the invention. See Manual of Patent
Examining Procedure §211.05. So the new or altered claims must
align with the original description. Ibid. ; see 35
U. S. C. §112. 2 The limit set out in Westinghouse is not often invoked today, because modern
courts construe patent claims (as they construe statutes) mainly by
reference to their text. See Lemley, Rethinking Assignor Estoppel,
54 Houston L. Rev. 513, 523 (2016). Only when the claims are
“still ambiguous,” after consideration of text and canons, will a
court think about narrowing a claim by reference to prior art. Phillips v. AWH Corp. , 415 F.3d 1303 , 1327 (CA Fed. 2005) (internal quotation marks
omitted). The critical point for our purpose is that even while
affirming the assignor estoppel doctrine, the Court made clear that
it did not always bar assignors from effectively defending against
infringement suits. 3 Recognizing this implicit
representation is particularly appropriate given the patent law’s
demand for honesty from patent applicants. In applying for a
patent, the inventor must ordinarily submit an oath—a statement
attesting that he is “the original inventor” of the “claimed
invention.” §115(b)(2); see supra , at 2. And the inventor
must comply with “a duty of candor and good faith” in the patent
process, including “a duty to disclose” to the PTO all information
he knows “to be material to patentability.” 37 CFR §1.56(a) (2020);
see §1.63(c). An inventor presenting an application to the PTO thus
states his good-faith belief that his claims are patentable—that
they will result in a valid patent. When the inventor then assigns
those claims to another, he effectively incorporates that
assurance. 4 Even beyond promoting
fairness, assignor estoppel furthers some patent policy goals.
Assignors are especially likely infringers because of their
knowledge of the relevant technology. By preventing them from
raising an invalidity defense in an infringement suit, the doctrine
gives assignees confidence in the value of what they have
purchased. That raises the price of patent assignments, and in turn
may encourage invention. SUPREME COURT OF THE UNITED STATES

															_________________

															No. 20–440

															_________________

															MINERVA SURGICAL, INC., PETITIONER v. HOLOGIC, INC., et al.

															on writ of certiorari to the united states
court of appeals for the federal circuit

															[June 29, 2021]

															Justice Alito, dissenting.

															We granted review in this case to decide whether
the doctrine of assignor estoppel bars petitioner from challenging
the validity of a patent indirectly assigned to respondents, and I
do not see how we can answer that question without deciding whether Westinghouse Elec. & Mfg. Co. v. Formica Insulation
Co. , 266 U.S.
342 (1924), which recognized assignor estoppel, should be
overruled. Both the majority and the principal dissent go to great
lengths to avoid that question, but in my judgment, their efforts
are unsuccessful.

															The majority says it has no need to invoke
precedent, see ante , at 13, but without that support, the
majority’s holding cannot stand. Not one word in the patent
statutes supports assignor estoppel, and the majority does not
claim otherwise. “[T]his Court [doesn’t] usually read into statutes
words that aren’t there,” Romag Fasteners, Inc. v. Fossil
Group, Inc. , 590 U. S. ___, ___ (2020) (slip op., at 3),
but that is just what the majority has done in this case.

															With so little support for its reasoning, it is
more than a little surprising that the majority forswears reliance
on precedent. See ante, at 13. Not too long ago, in Kimble v. Marvel Entertainment, LLC , 576 U.S. 446
(2015), another case involving a judicially created rule of patent
law, the Court applied a “superpowered form of stare
decisis .” Id ., at 458. Yet the majority refuses to wield
the nearly impregnable Kimble shield. Instead, it adopts a
text-blind method of statutory interpretation with which I cannot
possibly agree.

															The Court’s evasion of stare decisis is
fully matched by the principal dissent. That opinion sees no need
to address stare decisis because, in its view, Westinghouse has not been a precedent for the past 69 years.
According to the principal dissent, Westinghouse was
abrogated by the Patent Act of 1952. It reasons as follows: Westinghouse interpreted the Patent Act of 1870, post , at 1 (opinion of Barrett, J.); because that Act was
superseded by the Patent Act of 1952, we must decide whether the
new Act “ratified” Westinghouse, post , at 1; and in order to
show that Westinghouse was ratified, the defenders of
assignor estoppel must persuade us that “(1) the interpretation
[adopted in Westinghouse was] so well settled that we can
‘presume Congress knew of and endorsed it’ at the time of the
reenactment, and (2) the statute [was] reenacted without material
change,” post , at 2–3 (quoting Jama v. Immigration
and Customs Enforcement , 543 U.S.
335 , 349 (2005)).

															This reasoning is unprecedented and troubling.
To start, it is quite misleading to suggest that Westinghouse was based on an interpretation of the 1870
Patent Act. Neither of the two statutory provisions Westinghouse mentioned said anything that supported the
Court’s decision, and the Court did not claim otherwise.[ 1 ] Instead, the decision rested on
different grounds. It relied on the principle of “fair dealing,” an
analogy to the doctrine of estoppel by deed (a feature of the law
of real property), and perhaps most importantly, a body of lower
court case law. 266 U. S., at 348–352. If Westinghouse had been based on an interpretation of language in the 1870 Act and
if the 1952 Act had changed that language, there might be a basis
for finding abrogation.[ 2 ] But
that is not the situation here.

															After starting with this flawed premise, the
principal dissent adopts an ill-suited standard for determining
whether one of our precedents has been abrogated by
Congress. It applies a rule of interpretation that is patently
designed for a different purpose, i.e. , determining whether
congressional reenactment of a statute should be understood as a ratification of a preexisting body of lower court case
law .[ 3 ] That was the issue
in Jama , 543 U. S., at 349–352, the case the principal
dissent quotes, and that is why the rule asks whether the
interpretation in question is “well settled.” That question makes
sense as applied to a body of lower court cases, but what does that
mean with respect to one of our precedents? I would think that
endorsement by a majority of this Court is consensus enough.
Suggesting that a rule announced in a decision of this Court can
cease to be a precedent if it is not “well settled” is very
strange.

															Equally strange is the question whether we can
presume that Congress “knew of ” a decision of this Court
interpreting a statutory provision that it reenacts. Perhaps it is
hubris, but we have often presumed that Congress is aware of our
decisions. See, e.g., Ryan v. Valencia
Gonzales , 568 U.S.
57 , 66 (2013) (“We normally assume that, when Congress enacts
statutes, it is aware of relevant judicial precedent” (internal
quotation marks omitted)).

															When we reach the final part of the principal
dissent’s test for abrogating one of our precedents—whether the
statute in question was “reenacted without material change”—we
encounter further problems. The adjective “material” can mean
“[h]aving some logical connection with the consequential facts.”
Black’s Law Dictionary 1170 (11th ed. 2019). Thus, the principal
dissent can be read to say that a decision of this Court
interpreting a statutory provision is abrogated whenever a change
in the language of the statute provides some degree of support for
a different interpretation. The principal dissent cites no case in
which we have set the abrogation standard so low. And this new
“material change” standard for abrogating one of our precedents is
a marked departure from the standard advocated in one of the
principal dissent’s chosen treatises. See Reading Law 331
(“Legislative revision of law clearly established by judicial
opinion ought to be by express language or by unavoidably implied
contradiction”).[ 4 ]

															The principal dissent is forced to adopt this
new, low standard because it could not otherwise muster any sort of
argument for abrogation. The principal dissent cannot identify
anything in the 1952 Act that does away with the judge-made
doctrine of assignor estoppel “by express language or by
unavoidably implied contradiction.” Ibid . It cites 35
U. S. C. §282(b), which states that the invalidity of a
patent is a defense “in any action involving the validity or
infringement of a patent.” See post , at 1. But as the
majority notes, the patent laws contained similar language when Westinghouse was decided. Ante , at 10.

															The only modification made by the 1952 Act that
the principal dissent claims has any logical connection with
assignor estoppel is the addition of language saying that patents
generally have the attributes of personal property. See post , at 7. That change has a bearing on whether Westinghouse should be overruled because it undermined Westinghouse ’s analogy to estoppel by deed, but it is not
enough to show abrogation because Westinghouse did not rely
solely on that analogy.

															In sum, I do not think we can decide the
question that the petition in this case presents unless we decide
whether Westinghouse should be overruled.[ 5 ] Because the majority and the principal
dissent refuse to decide whether Westinghouse should be
overruled, I would dismiss the writ as improvidently granted. I
therefore respectfully dissent. Notes 1 One provision permitted
the assignment of patent rights, see Westinghouse , 266
U. S., at 348–349, and the other, which authorized the
granting of a patent to an assignee, was discussed in relation to
the scope of the doctrine of assignor estoppel, not its existence,
see id ., at 352. 2 By the same token, if
Congress had again used that particular language without change,
there might be a basis for finding ratification. See A. Scalia
& B. Garner, Reading Law: The Interpretation of Legal
Texts 322 (2012) (Reading Law) (prior-construction canon applies
when a “word or phrase has been authoritatively interpreted [and] a
later version of that act perpetuat[es] the wording”). 3 This is not to say that
Congress cannot pass statutes meant to incorporate this Court’s
interpretations of specific statutory language. Compare post , at 3, n. 3. It obviously can. What is unusual is
not the idea that Congress can ratify this Court’s decisions but
instead the application of a test designed to assess the
ratification of lower court decisions to assess the abrogation of a
decision of this Court. 4 The principal dissent
responds by noting that this passage in Reading Law sets out the
“ ‘express language’ ” or “ ‘unavoidably implied
contradiction’ ” standard as part of “an entirely different
canon.” Post , at 7, n. 4. That is precisely the point.
The passage discusses the standard that should be used when an
“authoritative judicial holding” is “cast in doubt and subjected to
challenge” by changes to a statutory scheme. Reading Law 331. The
rule applied by the principal dissent, on the other hand, is not
meant to assess congressional abrogation of our
precedents. 5 Under similar
circumstances in Kimble v. Marvel Entertainment, LLC ,
576 U.S. 446 (2015), every Member of this Court assessed a
judge-made patent-law doctrine through the lens of stare
decisis , see id ., at 455–465; id. , at 470–472
(Alito, J., dissenting), even though “Congress ha[d] repeatedly
amended . . . the specific provision . . . on
which [our earlier decision nominally] rested,” id ., at 456
(majority opinion). The principal dissent does not even cite Kimble , let alone make any effort to reconcile its novel
approach with that in our most analogous precedent. SUPREME COURT OF THE UNITED STATES

															_________________

															No. 20–440

															_________________

															MINERVA SURGICAL, INC., PETITIONER v. HOLOGIC, INC., et al.

															on writ of certiorari to the united states
court of appeals for the federal circuit

															[June 29, 2021]

															Justice Barrett, with whom Justice Thomas and
Justice Gorsuch join, dissenting.

															The Patent Act of 1952 sets forth a
comprehensive scheme for the creation and protection of patent
rights. But it nowhere mentions the equitable doctrine of assignor
estoppel, which precludes inventors who file patent applications
from later saying that the patent is invalid. To the contrary,
where the Act does address invalidity defenses, it states that
invalidity “shall” be a defense “in any action involving the
validity or infringement of a patent.” 35 U. S. C.
§282(b). The text includes no exception for actions in which the
inventor is the defendant.

															So why the doctrine of assignor estoppel?
Because in Westinghouse Elec. & Mfg. Co. v. Formica
Insulation Co. , 266 U.S.
342 (1924), we interpreted a predecessor statute, the Patent
Act of 1870, to incorporate the doctrine. The question before us is
whether the doctrine carried over into the Patent Act of 1952. That
could have happened in one of two ways: (1) if Congress ratified Westinghouse when it reenacted the assignment provision in
1952, or (2) if assignor estoppel was part of the well-settled
common-law backdrop against which Congress legislated in 1952. The
Court opts for the second theory, but in my view, neither
works.

															I

															I will take the possibility of congressional
ratification first because it follows more naturally from Westinghouse . In that case, the Court did not present the
doctrine of assignor estoppel as a well-established background
principle against which Congress legislated when it enacted the
Patent Act of 1870.[ 1 ] Nor
could it have: The first American case to apply the doctrine was
not decided until 1880. See Faulks v. Kamp , 3 F. 898
(CC SDNY). Instead, the Westinghouse Court identified
assignor estoppel as a rule that made sense in light of the Act’s
assignment provision. After examining the text of the provision,
the Court explained: “[T]here seems to be no reason why the
principles of estoppel by deed should not apply to assignment of a
patent right in accordance with the statute,” because “[i]t was
manifestly intended by Congress to surround the conveyance of
patent property with safeguards resembling those usually attaching
to that of land.” 266 U. S., at 348–349. Some lower courts had
applied the doctrine to the assignment and conveyance of patents,
and, giving that trend its blessing, the Court described assignor
estoppel as a sensible gloss on the assignment provision of the
1870 Act. Id., at 349–350.[ 2 ]

															The question here is whether Congress embraced
this gloss when it reenacted that provision in 1952. Congress
ratifies a judicial interpretation in a reenacted statute only if
two requirements are satisfied: (1) the interpretation must be so
well settled that we can “presume Congress knew of and endorsed it”
at the time of the reenactment, and (2) the statute must be
reenacted without material change. Jama v. Immigration
and Customs Enforcement , 543 U.S.
335 , 349, 351 (2005); Forest Grove School Dist. v. T.
A. , 557 U.S.
230 , 239–240 (2009); see also Lamar, Archer & Cofrin,
LLP v. Appling , 584 U. S. ___, ___ (2018) (slip
op., at 11) (noting that Congress incorporates a prior judicial
interpretation of a statute when it uses “the materially same
language” and the interpretation is “longstanding”); W. Eskridge,
Interpreting Law: A Primer on How to Read Statutes and the
Constitution 421–422 (2016) (“When Congress reenacts a statute, it
incorporates settled interpretations of the reenacted statute. The
rule is inapplicable when there is no settled standard Congress
could have known or the re-enactment makes a material change in the
text” (footnote omitted)). So here, respondents must persuade us
that (1) as of 1952, Westinghouse ’s construction of the
assignment provision in the Patent Act of 1870 was well settled,
and (2) the assignment provision in the Patent Act of 1952 is
materially identical to the 1870 version. Jama , 543
U. S., at 349. They cannot clear either hurdle.[ 3 ]

															A Westinghouse ’s construction of the
assignment provision in the Patent Act of 1870 was far from well
settled in 1952. Indeed, it is difficult to describe Westinghouse itself as much more than a “mild endorsement of
assignor estoppel.” Brief for Petitioner 20. While accepting the
doctrine, the Court simultaneously declined to apply it. Westinghouse , 266 U. S. , at 355 (holding that an
assignor could use prior art to narrow the patent claims); cf.
Brief for United States as Amicus Curiae 10 (“This Court has
never actually applied assignor estoppel in a case before it”).
Still, if Westinghouse had been the last word on assignor
estoppel, one might argue that it set forth a statement of a stable
principle.

															But Westinghouse was not the last word on
assignor estoppel. The next time we considered the doctrine, we
backpedaled. See Scott Paper Co. v. Marcalus Mfg.
Co. , 326 U.S.
249 (1945). Deeming Westinghouse ’s analysis a “logical
embarrassment,” we carved out an exception plainly inconsistent
with the general rule of assignor estoppel: that it does not apply
to an assignor who contests a patent’s validity by invoking an
expired patent. 326 U. S., at 253, 256–257. We also cast doubt
on the continuing validity of the doctrine, expressly declining to
address the extent to which assignor estoppel “may be deemed to
have survived the [ Westinghouse ] decision or to be
restricted by it.” Id., at 254. The dissent, for its part,
claimed that the Court had “repudiated judicially” assignor
estoppel altogether. Id., at 264 (opinion of Frankfurter,
J.); see also Edward Katzinger Co. v. Chicago Metallic
Mfg. Co. , 329 U.S.
394 , 400 (1947) (describing Scott Paper as holding that
an assignor could “challenge the validity” of a patent and “defeat
an action for infringement”).

															So when Congress reenacted the Patent Act in
1952, assignor estoppel was far from well settled—if anything, it
was on life support. Respondents could muster only three cases in
the seven years after Scott Paper (before Congress reenacted
the Patent Act) even loosely suggesting support for the doctrine.
See Brief for Respondents 6. Indeed, rather than embracing assignor
estoppel after Scott Paper , courts questioned the doctrine’s
validity. See, e.g., Douglass v. United States
Appliance Corp. , 177 F.2d 98, 101 (CA9 1949). Scholars did the
same; some, like the dissent in Scott Paper , concluded that
we had “wipe[d] out estoppel by assignment.” Lechner, Estoppel
Against Patent Assignors—The Scott Paper Company Case, 28 J. Pat.
Off. Soc. 325, 330 (1946). Others concluded that the law was a
mess. As one scholar put it: Westinghouse ’s rule “ has
become so unsettled during the past forty years of judicial
consideration that, today, some courts apparently consider the rule
to be no longer valid, others find no weakening of the rule, while
still other courts apply the rule only after considerable
speculation as to its continued validity.” Cooper, Estoppel To
Challenge Patent Validity: The Case of Private Good Faith vs.
Public Policy, 18 W. Res. L. Rev. 1122, 1123 (1967) (footnotes
omitted; emphasis added).

															Post-1952 judicial decisions addressing assignor
estoppel supply yet more evidence that the status of the doctrine
was (at best) uncertain when Congress reenacted the Patent Act. In Lear, Inc. v. Adkins , 395 U.S.
653 (1969), for example, we disavowed the closely related
doctrine of licensee estoppel, noting along the way that the
exception articulated in Scott Paper had “undermined the
very basis of the ‘general rule’ ” of assignor estoppel. 395
U. S., at 666. And following Lear , several lower courts
concluded that assignor estoppel was not just unsettled but, like
licensee estoppel, dead. See, e.g. , Coastal Dynamics
Corp. v. Symbolic Displays, Inc. , 469 F.2d 79 (CA9
1972).

															Tellingly, respondents could not come up with
even one case applying assignor estoppel in the nearly 20-year
period from Lear until the Federal Circuit resurrected the
doctrine in 1988. See Diamond Scientific Co. v. Ambico,
Inc. , 848 F.2d 1220, 1224–1225. And when the Federal Circuit
resurrected the doctrine, even it acknowledged that we had left the
vitality of assignor estoppel unsettled: “Although the Supreme
Court has examined th[e] doctrine . . . its opinions have
hardly been definite or definitive.” Id., at 1222.

															Given all this, it is hard to see how we can
“presume Congress knew of and endorsed” the doctrine when it
adopted a new version of the Patent Act in 1952. Jama , 543
U. S., at 349. That is so even if a technical parsing of Scott Paper finds that it left assignor estoppel not quite
dead, but ever-so-faintly breathing. In this circumstance, it would
be strange to conclude that the vitality of assignor estoppel was
so “unquestioned,” 543 U. S., at 349, that Congress would have
“regard[ed] the point as settled law,” A. Scalia & B. Garner,
Reading Law: The Interpretation of Legal Texts 325 (2012). On the
contrary, the law was anything but clear.

															Today’s opinion confirms as much. Although the
Court endorses assignor estoppel, it does not apply the doctrine as Westinghouse described it. Westinghouse stated the
“rule” of assignor estoppel this way: “[A]n assignor of a patent
right is estopped to attack the utility, novelty or validity of a
patented invention which he has assigned or granted as against any
one claiming the right under his assignment or grant.” 266
U. S., at 349. The Court describes assignor estoppel much more
narrowly: “The doctrine applies only when an inventor says one
thing (explicitly or implicitly) in assigning a patent and the
opposite in litigating against the patent’s owner.” Ante , at
5. This version of assignor estoppel does not appear in Westinghouse —nor, to my knowledge, in any other judicial
decision. The new version might be preferable to the old, but if
Congress truly had ratified Westinghouse , it would have
endorsed the Westinghouse version.

															B

															The reenactment canon has a second
requirement: The reenacted statute must be materially identical to
the one previously interpreted.[ 4 ] This poses another stumbling block for assignor
estoppel, because the assignment provision of the 1952 Act contains
a significant sentence that the 1870 Act did not: “Subject to the
provisions of this title, patents shall have the attributes of personal property .”[ 5 ]
Patent Act of 1952, §261, 66Stat. 810 (emphasis added). Given the
reasoning of Westinghouse , this is a material change. Westinghouse grounded its approval of
assignor estoppel in the idea that patents are like real property. After observing that the assignment provision required an
assignment to be made in writing and recorded in the Patent Office
within three months, the Court stated that “there seems to be no
reason why the principles of estoppel by deed should not apply to
assignment of a patent right in accordance with the statute.” 266
U. S., at 348–349. After all, the purpose of the
writing-and-recording requirement is to “furnish written and
recorded evidence of title and to protect the purchaser of the
title as recorded for value without notice.” Id., at 349.
Thus, the Court concluded, “[i]t was manifestly intended by
Congress to surround the conveyance of patent property with
safeguards” that resemble “those usually attaching to that of
land.” Ibid. But this analogy was inapt from the start. Even Westinghouse admitted that deeds and patents differed in an
important respect: “A tract of land is easily determined by survey.
Not so the scope of a patent right for an invention.” Id., at 350. Moreover, unlike the grantor of a deed, who guarantees the
quality of title, an assignor of a patent cannot warrant a patent’s
validity. The validity of a patent involves a factual and legal
inquiry “predicated on factors as to which reasonable men can
differ widely.” Lear , 395 U. S., at 670; see Stanford, Diamond Scientific Co . v. Ambico, Inc .: Enforcing
Patent Assignor Estoppel, 26 Houston L. Rev. 761, 766 (1989)
(“Since validity is never contractually transferred in an
assignment, there is no theoretical basis for assignor estoppel by
deed” (footnote omitted)).

															In any event, however persuasive we found the
patent-deed analogy in Westinghouse , the Patent Act of 1952
unraveled it. When Congress reenacted the assignment provision, it
specified that patents have “the attributes of personal
property .” 66Stat. 810 (emphasis added). Because this language
is inconsistent with the premise on which Westinghouse rested, it undercuts the argument that Congress ratified Westinghouse in the new assignment provision. Cf. Holder v. Martinez Gutierrez , 566
U.S. 583 , 593 (2012) (concluding that a reenacted provision did
not ratify a prior judicial construction where the provision lacked
the word on which the earlier construction was based).

															Respondents try to brush off the change as
insignificant, asserting that this “sentence has no bearing on
assignor estoppel anyway, because estoppel by deed, upon which
assignor estoppel is based, can apply to real or personal
property.” Brief for Respondents 20 (internal quotation marks
omitted). But whatever the scope of estoppel by deed—respondents do
not elaborate— Westinghouse expressly rested on “[t]he
analogy between estoppel in conveyances of land and estoppel
in assignments of a patent right.” 266 U. S., at 350 (emphasis
added). In the one case, a “grantor purports to convey the right to
exclude others . . . from a defined tract of land, and in
the other, from a described and limited field of the useful arts.” Ibid . By making clear that patents have “the attributes of
personal property,” Congress directly undermined an interpretation
that treated patents like deeds conveying land.

															II

															If Congress did not ratify our gloss on the
assignment provision in the 1952 Act, how else might assignor
estoppel be part of the statute? The Court comes at the
interpretive problem from a different angle: It holds that by 1952,
assignor estoppel had become “a background principle of patent
adjudication” against which Congress legislated. Ante, at
10. On this theory, Westinghouse is important not for its
interpretation of the assignment provision but for the equitable
principle that it endorsed. In my view, this theory also fails
because Westinghouse proved to be a false start for the
doctrine.

															We have said that “where a common-law principle
is well established, . . . courts may take it as given
that Congress has legislated with an expectation that the principle
will apply” absent statutory cues to the contrary. Astoria Fed.
Sav. & Loan Assn. v. Solimino , 501 U.S.
104 , 108 (1991); see also Eskridge, Interpreting Law, at 348
(“[C]ourts will assume that legislatures act against the background
of the common law”). So, for example, a federal statute of
limitations ordinarily is subject to equitable tolling even when
the text is silent because “Congress must be presumed to draft
limitations periods in light of this background principle.” Young v. United States , 535 U.S.
43 , 49–50 (2002); see also Nelson, Statutory Interpretation, at
629 (“[C]ourts frequently understand federal statutes to come with
some unstated qualifications or embellishments suggested by
principles of general jurisprudence”).

															The Court says that assignor estoppel works this
way too. Ante, at 10. True, the Patent Act provides that
“[i]nvalidity of the patent shall be a defense[ ] in any
action involving” infringement. Ibid. (quoting 35
U. S. C. §282(b); internal quotation marks and some
alterations omitted). Yet, the Court reasons, this apparently
absolute language does not “foreclose applying in patent cases a
whole host of common-law preclusion doctrines,” including
“equitable estoppel, collateral estoppel, res judicata, and law of
the case.” Ante, at 10. Assignor estoppel, the Court says,
falls in that same category. Ibid. According to the Court, Westinghouse confirmed a trend that had already begun in the
lower courts and has continued unabated since, giving assignor
estoppel a place in the pantheon of well-established common-law
principles.

															I disagree. The common-law pedigree of assignor
estoppel differs markedly from that of the preclusion doctrines
with which the Court groups it. Some of those doctrines have been
around for nearly a thousand years, see, e.g., Bursak, Note,
Preclusions, 91 N. Y. U. L. Rev. 1651, 1663 (2016) (“Res
judicata had migrated to England no later than the early 1100s”);
Millar, The Historical Relation of Estoppel by Record to Res
Judicata, 35 Ill. L. Rev. 41, 44–45 (1940) (res judicata and
collateral estoppel go back to at least the 1200s), and were far
more settled in early American courts, see, e.g., Washington, Alexandria, & Georgetown Steam-Packet Co. v. Sickles , 24 How. 333, 341 (1861) (“The authority of the res judicata . . . is derived by us from the Roman
law and the Canonists”); Hopkins v. Lee , 6 Wheat.
109, 114 (1821) (stating that collateral estoppel has “found its
way into every system of jurisprudence”). They are firmly rooted in
our jurisprudence now.

															Assignor estoppel, by contrast, has far from
this kind of “impeccable historic pedigree.” Kirtsaeng v. John Wiley & Sons, Inc. , 568 U.S.
519 , 538 (2013). It is more recent and far shakier. It was
introduced into patent law in the late 19th century—about a hundred
years after Congress enacted the first patent laws and a decade
after Congress passed the 1870 Act. See Faulks v. Kamp , 3 F. 898 (CC SDNY 1880); ante, at 6 (opinion of
the Court). And after its introduction, it lacked staying power. Westinghouse proved to be the “high-water mark of the
doctrine in this Court.” Brief for Petitioner 20. As I have already
explained, lower courts, commentators, the Scott Paper dissent, and even the Court itself in Lear regarded Scott
Paper as having gutted the doctrine of assignor estoppel. See supra, at 4–6.

															It is therefore difficult for me to see how, in
1952, assignor estoppel constituted a “long-established and
familiar principl[e]” like res judicata. Isbrandtsen Co. v. Johnson , 343 U.S.
779 , 783 (1952). At most, the doctrine of assignor estoppel was
in a confused state by 1952—a far cry from the high bar that we
have required to incorporate “well-settled” common-law background
principles into a statute. See, e.g., Kirtsaeng , 568
U. S., at 538 (noting the first-sale doctrine’s “impeccable
historic pedigree”); Lozano v. Montoya Alvarez , 572 U.S.
1 , 10 (2014) (emphasizing that equitable tolling is a
“long-established feature of American jurisprudence”). Indeed,
whatever one might have said when the Court decided Westinghouse in 1924, Scott Paper cut sharply in the
other direction. And such “contradictory signals are not typically
the stuff of which background rules of common law are made.” B&B Hardware, Inc. v. Hargis Industries, Inc. ,
575 U.S. 138, 163 (2015) (Thomas, J., dissenting).

															III

															Respondents insist that assignor estoppel
promotes fair dealing, while petitioner protests that the
supposedly equitable doctrine is actually inequitable in practice.
If we had authority to develop federal common law on the subject,
we could take sides in that debate. But no one contends that we do.
This case turns on whether the Patent Act of 1952 incorporates the
doctrine, and because it does not, I respectfully dissent. Notes 1 I do not understand the
Court to have a contrary view—its position is that assignor
estoppel had become a well-established background principle of
patent adjudication by the time Congress enacted the Patent Act of
1952. Ante, at 10. I address this possibility in Part II, infra . 2 Justice Alito maintains
that Westinghouse did not interpret the statute because it
made no effort to parse the text. Ante, at 2–3 (dissenting
opinion). But whatever the decision’s merits, it plainly grounded
assignor estoppel in the statute’s assignment provision. See Westinghouse , 266 U. S., at 348–349. 3 Justice Alito suggests
that the reenactment canon has no application when this Court, as
opposed to lower courts, has interpreted the prior version of a
statute. Ante, at 3–4. He is mistaken. As a leading treatise
explains, the canon has its most obvious application when a “court
of last resort” interprets a statute, though it “applies as well to
uniform holdings of lower courts and even to well-established
agency interpretations.” A. Scalia & B. Garner, Reading Law:
The Interpretation of Legal Texts 323–324 (2012) (footnote
omitted); see also C. Nelson, Statutory Interpretation 479 (2011)
(noting that the canon applies when “[t]he Supreme Court (or a
critical mass of lower courts, or an agency that Congress has put
in charge of administering the statute) adopt[s] a prominent
interpretation of one of the statute’s provisions”); Forest
Grove School Dist. v. T. A. , 557
U.S. 230 , 239 (2009) (applying the canon to a statute that we
had previously interpreted and that Congress had reenacted without
material change); Shapiro v. United States , 335 U.S.
1 , 16, 20 (1948) (same). To be sure, there is a practical
difference between the canon’s application to this Court and lower
courts: It takes a “uniform and sufficiently numerous” body of
lower court decisions to satisfy the presumption of congressional
notice, whereas a single decision of this Court can be enough.
Scalia, Reading Law, at 325; see, e.g., Forest Grove ,
557 U. S., at 239; Manhattan Properties, Inc. v. Irving Trust Co. , 291 U.S.
320 , 336 (1934); cf. BP p.l.c. v. Mayor and City
Council of Baltimore , 593 U. S. ___, ___ (2021) (slip op.,
at 11). But if a decision of this Court is oblique or thrown into
doubt by subsequent precedent—both of which are true here—we have
no basis for presuming that Congress was on notice of and endorsed
our position. See Forest Grove , 557 U. S., at
239. 4 Justice Alito argues that
the “material change” standard requires “express language” or
“unavoidably implied contradiction.” Ante, at 4 (internal
quotation marks omitted). He draws this heightened standard from an
entirely different canon—the presumption that a later enacted
statute does not impliedly repeal a former one. See ibid. ;
Scalia, Reading Law, at 327–333 (describing the “Presumption
Against Implied Repeal”). As for the canon applicable here—the
reenactment canon—our precedents do not support Justice Alito’s
proposed standard. See, e.g., Lorillard v. Pons , 434 U.S.
575 , 580 (1978) (“Congress is presumed to be aware of [a]
judicial interpretation of a statute and to adopt that
interpretation when it re-enacts a statute without change”); Forest Grove , 557 U. S., at 239–240 (same); see also Lamar, Archer & Cofrin, LLP v. Appling , 584
U. S. ___, ___ (2018) (slip op., at 11) (Congress is presumed
to be aware of a prior judicial interpretation of a statute when it
uses “the materially same language” in a subsequent statute). The
implied repeal canon addresses a different situation: when a court
interprets two different and arguably conflicting statutory
provisions. Scalia, Reading Law, at 331. 5 The Patent Act of 1870
provides, in relevant part: “[E]very patent or any interest therein
shall be assignable in law, by an instrument in writing; and the
patentee or his assigns or legal representatives may, in like
manner, grant and convey an exclusive right under his patent to the
whole or any specified part of the United States; and said
assignment, grant, or conveyance shall be void as against any
subsequent purchaser or mortgagee for a valuable consideration,
without notice, unless it is recorded in the patent office within
three months from the date thereof.” §36, 16Stat. 203; see Westinghouse , 266 U. S., at 348 (citing to the revised
version of the 1870 Act, “§4898”).

Summary:
Here is a summary of the case:

Minerva Surgical, Inc. v. Hologic, Inc.:

- The case concerns the patent for a device used to treat abnormal uterine bleeding invented by Csaba Truckai, a founder of Novacept, Inc.
- Truckai assigned his interest in the patent to Novacept, which was later acquired by Hologic, Inc.
- Minerva Surgical, a competitor, argued that Hologic's patent was invalid due to obviousness.
- The Court upheld the doctrine of "assignor estoppel," which prevents an inventor from assigning a patent to another entity for value and later challenging its validity.
- The Court clarified that assignor estoppel applies only when the assignor's claim of invalidity contradicts explicit or implicit representations made during the assignment.
- The Court emphasized the importance of fair dealing and the need to balance the interests of inventors and assignees.

This decision upholds the longstanding doctrine of assignor estoppel while providing clarity on its scope and application.