Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.

OCTOBER TERM, 2001

															Syllabus

															FESTO CORP. v. SHOKETSU KINZOKU KOGYO KABUSHIKI CO., LTD., ET AL.

															CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR THE FEDERAL
CIRCUIT No. 00-1543. Argued January 8, 2002-Decided May 28, 2002 Petitioner Festo Corporation owns two patents for an industrial
device.

															When the patent examiner rejected the initial application for
the first patent because of defects in description, 35 U. S. C. §
112, the application was amended to add the new limitations that
the device would contain a pair of one-way sealing rings and that
its outer sleeve would be made of a magnetizable material. The
second patent was also amended during a reexamination proceeding to
add the sealing rings limitation. After Festo began selling its
device, respondents (hereinafter SMC) entered the market with a
similar device that uses one two-way sealing ring and a
nonmagnetizable sleeve. Festo filed suit, claiming that SMC's
device is so similar that it infringes Festo's patents under the
doctrine of equivalents. The District Court ruled for Festo,
rejecting SMC's argument that the prosecution history estopped
Festo from saying that SMC's device is equivalent. A Federal
Circuit panel initially affirmed, but this Court granted
certiorari, vacated, and remanded in light of Warner-Jenkinson
Co. v. Hilton Davis Chemical Co., 520 U. S. 17 ,29, which had
acknowledged that competitors may rely on the prosecution history
to estop the patentee from recapturing subject matter surrendered
by amendment as a condition of obtaining the patent. On remand, the
en banc Federal Circuit reversed, holding that prosecution history
estoppel applied. The court ruled that estoppel arises from any
amendment that narrows a claim to comply with the Patent Act, not
only from amendments made to avoid the prior art, as the District
Court had held. The Federal Circuit also held that, when estoppel
applies, it bars any claim of equivalence for the element that was
amended. The court acknowledged that, under its prior cases,
prosecution history estoppel constituted a flexible bar,
foreclosing some, but not all, claims of equivalence, depending on
the purpose of the amendment and the alterations in the text.
However, the court overruled its precedents on the ground that
their case-by-case approach had proved unworkable. Held: Prosecution history estoppel may apply to any claim
amendment made to satisfy the Patent Act's requirements, not just
to amendments made to avoid the prior art, but estoppel need not
bar suit against every equivalent to the amended claim element.
Pp.730-742. 723 (a) To enable a patent holder to know what he owns, and the
public to know what he does not, the inventor must describe his
work in "full, clear, concise, and exact terms." § 112. However,
patent claim language may not describe with complete precision the
range of an invention's novelty. If patents were always interpreted
by their literal terms, their value would be greatly diminished.
Insubstantial substitutes for certain elements could defeat the
patent, and its value to inventors could be destroyed by simple
acts of copying. Thus, a patent's scope is not limited to its
literal terms, but embraces all equivalents to the claims
described. See Winans v. Denmead, 15 How. 330, 347.
Nevertheless, because it may be difficult to determine what is, or
is not, an equivalent, competitors may be deterred from engaging in
legitimate manufactures outside the patent's limits, or lulled into
developing competing products that the patent secures, thereby
prompting wasteful litigation. Each time the Court has considered
the doctrine of equivalents, it has acknowledged this uncertainty
as the price of ensuring the appropriate incentives for innovation,
and it has affirmed the doctrine over dissents that urged a more
certain rule. See, e. g., id., at 343, 347. Most
recently, Warner-Jenkinson, supra, at 28, reaffirmed the
doctrine. Pp. 730-733.

															(b) Prosecution history estoppel requires that patent claims be
interpreted in light of the proceedings before the Patent and
Trademark Office (PTO). When the patentee originally claimed the
subject matter alleged to infringe but then narrowed the claim in
response to a rejection, he may not argue that the surrendered
territory comprised an unforeseen equivalent. See Exhibit Supply
Co. v. Ace Patents Corp., 315 U. S. 126 , 136-137.
The rejection indicates that the patent examiner does not believe
the original claim could be patented. While the patentee has the
right to appeal, his decision to forgo an appeal and submit an
amended claim is taken as a concession that the invention as
patented does not reach as far as the original claim. See, e.
g., Goodyear Dental Vulcanite Co. v. Davis, 102 U. S. 222 , 228. Were
it otherwise, the inventor might avoid the PTO's gatekeeping role
and seek to recapture in an infringement action the very subject
matter surrendered as a condition of receiving the patent. pp.
733-735.

															(c) Prosecution history estoppel is not limited to amendments
intended to narrow the patented invention's subject matter, e. g., to avoid prior art, but may apply to a
narrowing amendment made to satisfy any Patent Act requirement,
including § 112's requirements concerning the patent application's
form. In Warner-Jenkinson, the Court made clear that
estoppel applies to amendments made for a "substantial reason
related to patentability," 520 U. S., at 33, but did not purport to
catalog every reason that might raise an estoppel. Indeed, it
stated that even 724 Syllabus

															if the amendment's purpose were unrelated to patentability, the
court might consider whether it was the kind of reason that
nonetheless might require estoppel. Id., at 40-41. Simply
because estoppel has been discussed most often in the context of
amendments made to avoid the prior art, see, e. g., id., at 30, it does not follow that amendments made for other
purposes will not give rise to estoppel. Section 112 requires that
the application describe, enable, and set forth the best mode of
carrying out the invention. The patent should not issue if these
requirements are not satisfied, and an applicant's failure to meet
them could lead to the issued patent being held invalid in later
litigation. Festo's argument that amendments made to comply with §
112 concern the application's form and not the invention's subject
matter conflates the patentee's reason for making the amendment
with the impact the amendment has on the subject matter. Estoppel
arises when an amendment is made to secure the patent and the
amendment narrows the patent's scope. If a § 112 amendment is truly
cosmetic, it would not narrow the patent's scope or raise an
estoppel. But if a § 112 amendment is necessary and narrows the
patent's scope-even if only for better description-estoppel may
apply. Pp.735-737.

															(d) Prosecution history estoppel does not bar the inventor from
asserting infringement against every equivalent to the narrowed
element. Though estoppel can bar challenges to a wide range of
equivalents, its reach requires an examination of the subject
matter surrendered by the narrowing amendment. The Federal
Circuit's complete bar rule is inconsistent with the purpose of
applying the estoppel in the first place-to hold the inventor to
the representations made during the application process and the
inferences that may be reasonably drawn from the amendment. By
amending the application, the inventor is deemed to concede that
the patent does not extend as far as the original claim, not that
the amended claim is so perfect in its description that no one
could devise an equivalent. The Court's view is consistent with
precedent and PTO practice. The Court has consistently applied the
doctrine in a flexible way, considering what equivalents were
surrendered during a patent's prosecution, rather than imposing a
complete bar that resorts to the very literalism the equivalents
rule is designed to overcome. E. g., Goodyear
Dental, supra, at 230. The Federal Circuit ignored Warner-Jenkinson's instruction that courts must be cautious
before adopting changes that disrupt the settled expectations of
the inventing community. See 520 U. S., at 28. Inventors who
amended their claims under the previous case law had no reason to
believe they were conceding all equivalents. Had they known, they
might have appealed the rejection instead. Warner-Jenkinson struck the appropriate balance by placing the burden on the
patentee to prove that an 725 amendment was not made for a reason that would give rise to
estoppel. Id., at 33. Similarly, the patentee should bear
the burden of showing that the amendment does not surrender the
particular equivalent in question. As the author of the claim
language, his decision to narrow his claims through amendment may
be presumed to be a general disclaimer of the territory between the
original claim and the amended claim. Exhibit Supply, supra, at 136-137. However, in cases in which the amendment cannot
reasonably be viewed as surrendering a particular equivalent--e. g., where the equivalent was unforeseeable at the time of
the application or the rationale underlying the amendment bears but
a tangential relation to the equivalent-the patentee can rebut the
presumption that prosecution history estoppel bars a finding of
equivalence by showing that at the time of the amendment one
skilled in the art could not reasonably be expected to have drafted
a claim that would have literally encompassed the alleged
equivalent. Pp.737-741.

															(e) Whether Festo has rebutted the presumptions that estoppel
applies and that the equivalents at issue have been surrendered
should be determined in the first instance by further proceedings
below. Pp. 741-742. 234 F.3d
558 , vacated and remanded.

															KENNEDY, J., delivered the opinion for a unanimous Court.

															Robert H. Bork argued the cause for petitioner. With him on the
briefs were Charles R. Hoffmann, Gerald T. Bodner, Glenn T.
Henneberger, Anthony E. Bennett, Andrew L. Frey, Donald M. Falk,
and Robert L. Bronston.

															Deputy Solicitor General Wallace argued the cause for the United
States as amicus curiae. With him on the brief were Solicitor
General Olson, Acting Assistant Attorney General Schiffer, Jeffrey
P. Minear, Vito J. DiPietro, Anthony J. Steinmeyer,
Howard S. Scher, and Linda Moneys Isacson. Arthur 1. Neustadt argued the cause for
respondents.

															With him on the brief were Charles L. Gho lz, Robert T. Pous,
and James B. Lampert. * *Briefs of amici curiae urging reversal were filed for
the American Bar Association by Robert E. Hirshon, E. Anthony
Figg, Minaksi Bhatt, and Robert H. Cameron; for the
American Intellectual Property Law Association by Lawrence M.
Sung and Janice M. Mueller; for ASTA Medica 726 JUSTICE KENNEDY delivered the opinion of the Court. This case
requires us to address once again the relation between two patent
law concepts, the doctrine of equivalents and the rule of
prosecution history estoppel. The Court considered the same
concepts in Warner-Jenkinson Co. v. Hilton Davis Chemical
Co., 520 U. S.
17 (1997), and reaf-

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des Conseils en Propriete Industrielle by Maxim H. Waldbaum,
Raymond C. Stewart, John P. Sutton, and Tipton D. Jennings IV; for
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Winter; for Litton Systems, Inc., by John G. Roberts, Jr.,
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by Carter G. Phillips, Joseph R. Guerra, Mark E. Haddad, Gary L.
Griswold, Robert A. Armitage, Philip S. Johnson, Wayne C. Jaeschke,
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Moses; for the National Intellectual Property Law Institute by
James Phillip Chandler; for the Wisconsin Alumni Research
Foundation et al. by Susan G. Braden, Kevin M. O'Brien, and Michael
E. Murphy; and for Vincent P. Tassinari by Mr. Tassinari, pro
se.

															Briefs of amici curiae urging affirmance were filed for the
Consumer Project on Technology by Joshua D. Sarnoff; for Genentech,
Inc., by Jeffrey P. Kushan and Marinn F. Carlson; for Intel Corp.
et al. by Terry E. Fenzl, Alan H. Blankenheimer, and Howard Ross
Cabot; and for International Business Machines Corp. et al. by
Christopher A. Hughes, Mark J. Abate, Frederick T. Boehm,
Mark F. Chadurjian, William J. Coughlin, Barry Estrin, and
Richard Whiting.

															Briefs of amici curiae were filed for Applera Corp. et
al. by Matthew D. Powers and Edward R. Reines; for
the Institute of Electrical and Electronics Engineers-United States
of America by Andrew C. Greenberg and Matthew J. Conigliaro; for Medimmune, Inc., by Harvey
Kurzweil and Henry J. Ricardo; for the
Patent, Trademark, & Copyright Section of the Bar Association
of the District of Columbia by William P. Atkins; for the
Philadelphia Intellectual Property Law Association by Joan Taft
Kluger and Manny D. Pokotilow; and for Sean Patrick
Suiter by Mr. Suiter, pro se. 727 firmed that a patent protects its holder against efforts of
copyists to evade liability for infringement by making only
insubstantial changes to a patented invention. At the same time, we
appreciated that by extending protection beyond the literal terms
in a patent the doctrine of equivalents can create substantial
uncertainty about where the patent monopoly ends. Id., at
29. If the range of equivalents is unclear, competitors may be
unable to determine what is a permitted alternative to a patented
invention and what is an infringing equivalent.

															To reduce the uncertainty, Warner-Jenkinson acknowledged
that competitors may rely on the prosecution history, the public
record of the patent proceedings. In some cases the Patent and
Trademark Office (PTO) may have rejected an earlier version of the
patent application on the ground that a claim does not meet a
statutory requirement for patentability. 35 U. S. C. § 132 (1994
ed., Supp. V). When the patentee responds to the rejection by
narrowing his claims, this prosecution history estops him from
later arguing that the subject matter covered by the original,
broader claim was nothing more than an equivalent. Competitors may
rely on the estoppel to ensure that their own devices will not be
found to infringe by equivalence.

															In the decision now under review the Court of Appeals for the
Federal Circuit held that by narrowing a claim to obtain a patent,
the patentee surrenders all equivalents to the amended claim
element. Petitioner asserts this holding departs from past
precedent in two respects. First, it applies estoppel to every
amendment made to satisfy the requirements of the Patent Act and
not just to amendments made to avoid pre-emption by an earlier
invention, i. e., the prior art. Second, it holds that when
estoppel arises, it bars suit against every equivalent to the
amended claim element. The Court of Appeals acknowledged that this
holding departed from its own cases, which applied a flexible bar
when considering what claims of equivalence were estopped by
the 728 prosecution history. Petitioner argues that by replacing the
flexible bar with a complete bar the Court of Appeals cast doubt on
many existing patents that were amended during the application
process when the law, as it then stood, did not apply so rigorous a
standard.

															We granted certiorari to consider these questions.

															I

															Petitioner Festo Corporation owns two patents for an improved
magnetic rodless cylinder, a piston-driven device that relies on
magnets to move objects in a conveying system. The device has many
industrial uses and has been employed in machinery as diverse as
sewing equipment and the Thunder Mountain ride at Disney World.
Although the precise details of the cylinder's operation are not
essential here, the prosecution history must be considered.

															Petitioner's patent applications, as often occurs, were amended
during the prosecution proceedings. The application for the first
patent, the Stoll Patent (D. S. Patent No. 4,354,125), was amended
after the patent examiner rejected the initial application because
the exact method of operation was unclear and some claims were made
in an impermissible way. (They were multiply dependent.) 35 D. S.
C. § 112 (1994 ed.). The inventor, Dr. Stoll, submitted a new
application designed to meet the examiner's objections and also
added certain references to prior art. 37 CFR § 1.56 (2000). The
second patent, the Carroll Patent (D. S. Patent No. 3,779,401), was
also amended during a reexamination proceeding. The prior art
references were added to this amended application as well. Both
amended patents added a new limitation-that the inventions contain
a pair of sealing rings, each having a lip on one side, which would
prevent impurities from getting on the piston assembly. The amended
Stoll Patent added the further limitation that the outer shell of
the device, the sleeve, be made of a magnetizable material. 729 After Festo began selling its rodless cylinder, respondents
(whom we refer to as SMC) entered the market with a device similar,
but not identical, to the ones disclosed by Festo's patents. SMC's
cylinder, rather than using two one-way sealing rings, employs a
single sealing ring with a two-way lip. Furthermore, SMC's sleeve
is made of a nonmagnetizable alloy. SMC's device does not fall
within the literal claims of either patent, but petitioner contends
that it is so similar that it infringes under the doctrine of
equivalents.

															SMC contends that Festo is estopped from making this argument
because of the prosecution history of its patents. The sealing
rings and the magnetized alloy in the Festo product were both
disclosed for the first time in the amended applications. In SMC's
view, these amendments narrowed the earlier applications,
surrendering alternatives that are the very points of difference in
the competing devices-the sealing rings and the type of alloy used
to make the sleeve. As Festo narrowed its claims in these ways in
order to obtain the patents, says SMC, Festo is now estopped from
saying that these features are immaterial and that SMC's device is
an equivalent of its own.

															The United States District Court for the District of
Massachusetts disagreed. It held that Festo's amendments were not
made to avoid prior art, and therefore the amendments were not the
kind that give rise to estoppel. A panel of the Court of Appeals
for the Federal Circuit affirmed. 72 F.3d
857 (1995). We granted certiorari, vacated, and remanded in
light of our intervening decision in Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U. S. 17 (1997). After
a decision by the original panel on remand, 172
F.3d 1361 (1999), the Court of Appeals ordered rehearing en
banc to address questions that had divided its judges since our
decision in Warner-Jenkinson. 187 F.3d
1381 (1999).

															The en banc court reversed, holding that prosecution history
estoppel barred Festo from asserting that the accused device
infringed its patents under the doctrine of equiva- 730 lents. 234 F.3d
558 (2000). The court held, with only one judge dissenting,
that estoppel arises from any amendment that narrows a claim to
comply with the Patent Act, not only from amendments made to avoid
prior art. Id., at 566. More controversial in the Court of
Appeals was its further holding: When estoppel applies, it stands
as a complete bar against any claim of equivalence for the element
that was amended. Id., at 574-575. The court acknowledged
that its own prior case law did not go so far. Previous decisions
had held that prosecution history estoppel constituted a flexible
bar, foreclosing some, but not all, claims of equivalence,
depending on the purpose of the amendment and the alterations in
the text. The court concluded, however, that its precedents
applying the flexible-bar rule should be overruled because this
case-by-case approach has proved unworkable. In the court's view a
complete-bar rule, under which estoppel bars all claims of
equivalence to the narrowed element, would promote certainty in the
determination of infringement cases.

															Four judges dissented from the decision to adopt a complete bar. Id., at 562. In four separate opinions, the dissenters
argued that the majority's decision to overrule precedent was
contrary to Warner-Jenkinson and would unsettle the
expectations of many existing patentees. Judge Michel, in his
dissent, described in detail how the complete bar required the
Court of Appeals to disregard 8 older decisions of this Court, as
well as more than 50 of its own cases. 234

															We granted certiorari. 533 U. S. 915 (2001).

															II

															The patent laws "promote the Progress of Science and useful
Arts" by rewarding innovation with a temporary monopoly. U. S.
Const., Art. I, § 8, cl. 8. The monopoly is a property right; and
like any property right, its boundaries should be clear. This
clarity is essential to promote progress, be- 731 cause it enables efficient investment in innovation. A patent
holder should know what he owns, and the public should know what he
does not. For this reason, the patent laws require inventors to
describe their work in "full, clear, concise, and exact terms," 35
U. s. C. § 112, as part of the delicate balance the law attempts to
maintain between inventors, who rely on the promise of the law to
bring the invention forth, and the public, which should be
encouraged to pursue innovations, creations, and new ideas beyond
the inventor's exclusive rights. Bonito Boats, Inc. v. Thunder Craft Boats, Inc., 489 U. S. 141 , 150
(1989).

															Unfortunately, the nature of language makes it impossible to
capture the essence of a thing in a patent application. The
inventor who chooses to patent an invention and disclose it to the
public, rather than exploit it in secret, bears the risk that
others will devote their efforts toward exploiting the limits of
the patent's language: "An invention exists most importantly as a tangible structure or
a series of drawings. A verbal portrayal is usually an afterthought
written to satisfy the requirements of patent law. This conversion
of machine to words allows for unintended idea gaps which cannot be
satisfactorily filled. Often the invention is novel and words do
not exist to describe it. The dictionary does not always keep
abreast of the inventor. It cannot. Things are not made for the
sake of words, but words for things." Autogiro Co. of
America v. United States, 384 F.2d
391 , 397 (Ct. Cl. 1967). The language in the patent claims may not capture every nuance
of the invention or describe with complete precision the range of
its novelty. If patents were always interpreted by their literal
terms, their value would be greatly diminished. Unimportant and
insubstantial substitutes for certain elements could defeat the
patent, and its value to inventors could be destroyed by simple
acts of copying. For this 732 reason, the clearest rule of patent interpretation, literalism,
may conserve judicial resources but is not necessarily the most
efficient rule. The scope of a patent is not limited to its literal
terms but instead embraces all equivalents to the claims described.
See Winans v. Denmead, 15 How. 330, 347 (1854).

															It is true that the doctrine of equivalents renders the scope of
patents less certain. It may be difficult to determine what is, or
is not, an equivalent to a particular element of an invention. If
competitors cannot be certain about a patent's extent, they may be
deterred from engaging in legitimate manufactures outside its
limits, or they may invest by mistake in competing products that
the patent secures. In addition the uncertainty may lead to
wasteful litigation between competitors, suits that a rule of
literalism might avoid. These concerns with the doctrine of
equivalents, however, are not new. Each time the Court has
considered the doctrine, it has acknowledged this uncertainty as
the price of ensuring the appropriate incentives for innovation,
and it has affirmed the doctrine over dissents that urged a more
certain rule. When the Court in Winans v. Denmead,
supra, first adopted what has become the doctrine of
equivalents, it stated that "[t]he exclusive right to the thing
patented is not secured, if the public are at liberty to make
substantial copies of it, varying its form or proportions." Id., at 343. The dissent argued that the Court had
sacrificed the objective of "[f]ul[l]ness, clearness, exactness,
preciseness, and particularity, in the description of the
invention." Id., at 347 (opinion of Campbell, J.).

															The debate continued in Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U. S. 605 (1950),
where the Court reaffirmed the doctrine. Graver Tank held
that patent claims must protect the inventor not only from those
who produce devices falling within the literal claims of the patent
but also from copyists who "make unimportant and insubstantial
changes and substitutions in the patent which, though adding 733 nothing, would be enough to take the copied matter outside the
claim, and hence outside the reach of law." Id., at 607.
Justice Black, in dissent, objected that under the doctrine of
equivalents a competitor "cannot rely on what the language of a
patent claims. He must be able, at the peril of heavy infringement
damages, to forecast how far a court relatively unversed in a
particular technological field will expand the claim's language
.... " Id., at 617.

															Most recently, in Warner-Jenkinson, the Court reaffirmed
that equivalents remain a firmly entrenched part of the settled
rights protected by the patent. A unanimous opinion concluded that
if the doctrine is to be discarded, it is Congress and not the
Court that should do so: "[T]he lengthy history of the doctrine of equivalents strongly
supports adherence to our refusal in Graver Tank to find
that the Patent Act conflicts with that doctrine. Congress can
legislate the doctrine of equivalents out of existence any time it
chooses. The various policy arguments now made by both sides are
thus best addressed to Congress, not this Court." 520 U. S., at
28. III

															Prosecution history estoppel requires that the claims of a
patent be interpreted in light of the proceedings in the PTO during
the application process. Estoppel is a "rule of patent
construction" that ensures that claims are interpreted by reference
to those "that have been cancelled or rejected." Schriber-Schroth Co. v. Cleveland Trust Co., 311 U. S. 211 , 220-221
(1940). The doctrine of equivalents allows the patentee to claim
those insubstantial alterations that were not captured in drafting
the original patent claim but which could be created through
trivial changes. When, however, the patentee originally claimed the
subject matter alleged to infringe but then narrowed the claim in
response to a rejection, he may not argue that the surrendered
territory com- 734 prised unforeseen subject matter that should be deemed
equivalent to the literal claims of the issued patent. On the
contrary, "[b]y the amendment [the patentee] recognized and
emphasized the difference between the two phrases[,] ... and [t]he
difference which [the patentee] thus disclaimed must be regarded as
material." Exhibit Supply Co. v. Ace Patents Corp., 315 U. S. 126 ,
136-137 (1942).

															A rejection indicates that the patent examiner does not believe
the original claim could be patented. While the patentee has the
right to appeal, his decision to forgo an appeal and submit an
amended claim is taken as a concession that the invention as
patented does not reach as far as the original claim. See Goodyear Dental Vulcanite Co. v. Davis, 102 U. S.
222, 228 (1880) ("In view of [the amendment] there can be no doubt
of what [the patentee] understood he had patented, and that both he
and the commissioner regarded the patent to be for a manufacture
made exclusively of vulcanites by the detailed process"); Wang
Laboratories, Inc. v. Mitsubishi Electronics America,
Inc., 103 F.3d
1571 , 1577-1578 (CA Fed. 1997) ("Prosecution history
estoppel ... preclud[es] a patentee from regaining, through
litigation, coverage of subject matter relinquished during
prosecution of the application for the patent"). Were it otherwise,
the inventor might avoid the PTO's gatekeeping role and seek to
recapture in an infringement action the very subject matter
surrendered as a condition of receiving the patent.

															Prosecution history estoppel ensures that the doctrine of
equivalents remains tied to its underlying purpose. Where the
original application once embraced the purported equivalent but the
patentee narrowed his claims to obtain the patent or to protect its
validity, the patentee cannot assert that he lacked the words to
describe the subject matter in question. The doctrine of
equivalents is premised on language's inability to capture the
essence of innovation, but a prior application describing the
precise element at issue undercuts that premise. In that instance
the prosecution history has 735 established that the inventor turned his attention to the
subject matter in question, knew the words for both the broader and
narrower claim, and affirmatively chose the latter.

															A

															The first question in this case concerns the kinds of amendments
that may give rise to estoppel. Petitioner argues that estoppel
should arise when amendments are intended to narrow the subject
matter of the patented invention, for instance, amendments to avoid
prior art, but not when the amendments are made to comply with
requirements concerning the form of the patent application. In WarnerJenkinson we recognized that prosecution history
estoppel does not arise in every instance when a patent application
is amended. Our "prior cases have consistently applied prosecution
history estoppel only where claims have been amended for a limited
set of reasons," such as "to avoid the prior art, or otherwise to
address a specific concern-such as obviousness-that arguably would
have rendered the claimed subject matter unpatentable." 520 U. S.,
at 30-32. While we made clear that estoppel applies to amendments
made for a "substantial reason related to patentability," id., at 33, we did not purport to define that term or to
catalog every reason that might raise an estoppel. Indeed, we
stated that even if the amendment's purpose were unrelated to
patentability, the court might consider whether it was the kind of
reason that nonetheless might require resort to the estoppel
doctrine. Id., at 40-41.

															Petitioner is correct that estoppel has been discussed most
often in the context of amendments made to avoid the prior art. See Exhibit Supply Co., supra, at 137; Keystone Driller
Co. v. Northwest Engineering Corp., 294 U. S. 42 , 48 (1935).
Amendment to accommodate prior art was the emphasis, too, of our
decision in Warner-Jenkinson, supra, at 30. It does not
follow, however, that amendments for other purposes will not give
rise to estoppel. Prosecution 736 history may rebut the inference that a thing not described was
indescribable. That rationale does not cease simply because the
narrowing amendment, submitted to secure a patent, was for some
purpose other than avoiding prior art.

															We agree with the Court of Appeals that a narrowing amendment
made to satisfy any requirement of the Patent Act may give rise to
an estoppel. As that court explained, a number of statutory
requirements must be satisfied before a patent can issue. The
claimed subject matter must be useful, novel, and not obvious. 35
U. S. C. §§ 101-103 (1994 ed. and Supp. V). In addition, the patent
application must describe, enable, and set forth the best mode of
carrying out the invention. § 112 (1994 ed.). These latter
requirements must be satisfied before issuance of the patent, for
exclusive patent rights are given in exchange for disclosing the
invention to the public. See Bonito Boats, 489 U. S., at
150-151. What is claimed by the patent application must be the same
as what is disclosed in the specification; otherwise the patent
should not issue. The patent also should not issue if the other
requirements of § 112 are not satisfied, and an applicant's failure
to meet these requirements could lead to the issued patent being
held invalid in later litigation.

															Petitioner contends that amendments made to comply with § 112
concern the form of the application and not the subject matter of
the invention. The PTO might require the applicant to clarify an
ambiguous term, to improve the translation of a foreign word, or to
rewrite a dependent claim as an independent one. In these cases,
petitioner argues, the applicant has no intention of surrendering
subject matter and should not be estopped from challenging
equivalent devices. While this may be true in some cases,
petitioner's argument conflates the patentee's reason for making
the amendment with the impact the amendment has on the subject
matter.

															Estoppel arises when an amendment is made to secure the patent
and the amendment narrows the patent's scope. If a § 112 amendment
is truly cosmetic, then it would not narrow 737 the patent's scope or raise an estoppel. On the other hand, if a
§ 112 amendment is necessary and narrows the patent's scope-even if
only for the purpose of better descriptionestoppel may apply. A
patentee who narrows a claim as a condition for obtaining a patent
disavows his claim to the broader subject matter, whether the
amendment was made to avoid the prior art or to comply with § 112.
We must regard the patentee as having conceded an inability to
claim the broader subject matter or at least as having abandoned
his right to appeal a rejection. In either case estoppel may
apply.

															B

															Petitioner concedes that the limitations at issue-the sealing
rings and the composition of the sleeve-were made for reasons
related to § 112, if not also to avoid the prior art. Our
conclusion that prosecution history estoppel arises when a claim is
narrowed to comply with § 112 gives rise to the second question
presented: Does the estoppel bar the inventor from asserting
infringement against any equivalent to the narrowed element or
might some equivalents still infringe? The Court of Appeals held
that prosecution history estoppel is a complete bar, and so the
narrowed element must be limited to its strict literal terms. Based
upon its experience the Court of Appeals decided that the
flexible-bar rule is unworkable because it leads to excessive
uncertainty and burdens legitimate innovation. For the reasons that
follow, we disagree with the decision to adopt the complete
bar.

															Though prosecution history estoppel can bar a patentee from
challenging a wide range of alleged equivalents made or distributed
by competitors, its reach requires an examination of the subject
matter surrendered by the narrowing amendment. The complete bar
avoids this inquiry by establishing a per se rule; but that
approach is inconsistent with the purpose of applying the estoppel
in the first place-to hold the inventor to the representations made
during the application process and to the inferences that may
reason- 738 ably be drawn from the amendment. By amending the application,
the inventor is deemed to concede that the patent does not extend
as far as the original claim. It does not follow, however, that the
amended claim becomes so perfect in its description that no one
could devise an equivalent. After amendment, as before, language
remains an imperfect fit for invention. The narrowing amendment may
demonstrate what the claim is not; but it may still fail to capture
precisely what the claim is. There is no reason why a narrowing
amendment should be deemed to relinquish equivalents unforeseeable
at the time of the amendment and beyond a fair interpretation of
what was surrendered. Nor is there any call to foreclose claims of
equivalence for aspects of the invention that have only a
peripheral relation to the reason the amendment was submitted. The
amendment does not show that the inventor suddenly had more
foresight in the drafting of claims than an inventor whose
application was granted without amendments having been submitted.
It shows only that he was familiar with the broader text and with
the difference between the two. As a result, there is no more
reason for holding the patentee to the literal terms of an amended
claim than there is for abolishing the doctrine of equivalents
altogether and holding every patentee to the literal terms of the
patent.

															This view of prosecution history estoppel is consistent with our
precedents and respectful of the real practice before the PTO.
While this Court has not weighed the merits of the complete bar
against the flexible bar in its prior cases, we have consistently
applied the doctrine in a flexible way, not a rigid one. We have
considered what equivalents were surrendered during the prosecution
of the patent, rather than imposing a complete bar that resorts to
the very literalism the equivalents rule is designed to overcome. E. g., Goodyear Dental Vulcanite Co., 102 U. S., at
230; Hurlbut v. Schillinger, 130 U. S. 456 , 465
(1889). 739 The Court of Appeals ignored the guidance of WarnerJenkinson, which instructed that courts must be
cautious before adopting changes that disrupt the settled
expectations of the inventing community. See 520 U. S., at 28. In
that case we made it clear that the doctrine of equivalents and the
rule of prosecution history estoppel are settled law. The
responsibility for changing them rests with Congress. Ibid. Fundamental alterations in these rules risk destroying the
legitimate expectations of inventors in their property. The
petitioner in Warner-Jenkinson requested another bright-line
rule that would have provided more certainty in determining when
estoppel applies but at the cost of disrupting the expectations of
countless existing patent holders. We rejected that approach: "To
change so substantially the rules of the game now could very well
subvert the various balances the PTO sought to strike when issuing
the numerous patents which have not yet expired and which would be
affected by our decision." Id., at 32, n. 6; see also id., at 41 (GINSBURG, J., concurring) ("The new presumption,
if applied woodenly, might in some instances unfairly discount the
expectations of a patentee who had no notice at the time of patent
prosecution that such a presumption would apply"). As Warner-Jenkinson recognized, patent prosecution occurs in
the light of our case law. Inventors who amended their claims under
the previous regime had no reason to believe they were conceding
all equivalents. If they had known, they might have appealed the
rejection instead. There is no justification for applying a new and
more robust estoppel to those who relied on prior doctrine.

															In Warner-Jenkinson we struck the appropriate balance by
placing the burden on the patentee to show that an amendment was
not for purposes of patentability: "Where no explanation is established, however, the court should
presume that the patent application had a substantial reason
related to patentability for including the limiting element added
by amendment. In those 740 circumstances, prosecution history estoppel would bar the
application of the doctrine of equivalents as to that element." Id., at 33. When the patentee is unable to explain the reason for amendment,
estoppel not only applies but also "bar[s] the application of the
doctrine of equivalents as to that element." Ibid. These
words do not mandate a complete bar; they are limited to the
circumstance where "no explanation is established." They do
provide, however, that when the court is unable to determine the
purpose underlying a narrowing amendment-and hence a rationale for
limiting the estoppel to the surrender of particular
equivalents-the court should presume that the patentee surrendered
all subject matter between the broader and the narrower
language.

															Just as Warner-Jenkinson held that the patentee bears the
burden of proving that an amendment was not made for a reason that
would give rise to estoppel, we hold here that the patentee should
bear the burden of showing that the amendment does not surrender
the particular equivalent in question. This is the approach
advocated by the United States, see Brief for United States as Amicus Curiae 22-28, and we regard it to be sound. The
patentee, as the author of the claim language, may be expected to
draft claims encompassing readily known equivalents. A patentee's
decision to narrow his claims through amendment may be presumed to
be a general disclaimer of the territory between the original claim
and the amended claim. Exhibit Supply, 315 U. S., at 136-137
("By the amendment [the patentee] recognized and emphasized the
difference between the two phrases and proclaimed his abandonment
of all that is embraced in that difference"). There are some cases,
however, where the amendment cannot reasonably be viewed as
surrendering a particular equivalent. The equivalent may have been
unforeseeable at the time of the application; the rationale
underlying the amendment may bear no more than a tangential
relation to the equivalent in question; or there 741 may be some other reason suggesting that the patentee could not
reasonably be expected to have described the insubstantial
substitute in question. In those cases the patentee can overcome
the presumption that prosecution history estoppel bars a finding of
equivalence.

															This presumption is not, then, just the complete bar by another
name. Rather, it reflects the fact that the interpretation of the
patent must begin with its literal claims, and the prosecution
history is relevant to construing those claims. When the patentee
has chosen to narrow a claim, courts may presume the amended text
was composed with awareness of this rule and that the territory
surrendered is not an equivalent of the territory claimed. In those
instances, however, the patentee still might rebut the presumption
that estoppel bars a claim of equivalence. The patentee must show
that at the time of the amendment one skilled in the art could not
reasonably be expected to have drafted a claim that would have
literally encompassed the alleged equivalent.

															IV

															On the record before us, we cannot say petitioner has rebutted
the presumptions that estoppel applies and that the equivalents at
issue have been surrendered. Petitioner concedes that the
limitations at issue-the sealing rings and the composition of the
sleeve-were made in response to a rejection for reasons under §
112, if not also because of the prior art references. As the
amendments were made for a reason relating to patentability, the
question is not whether estoppel applies but what territory the
amendments surrendered. While estoppel does not effect a complete
bar, the question remains whether petitioner can demonstrate that
the narrowing amendments did not surrender the particular
equivalents at issue. On these questions, SMC may well prevail, for
the sealing rings and the composition of the sleeve both were noted
expressly in the prosecution history. These matters, however,
should be determined in the first instance 742 by further proceedings in the Court of Appeals or the District
Court.

															The judgment of the Federal Circuit is vacated, and the case is
remanded for further proceedings consistent with this opinion.

															It is so ordered.