No. 00-1543 

In the Supreme Court of the United States 

FESTO CORPORATION, PETITIONER 

v. 

SHOKETSU KINZOKU KOGYO KABUSHIKI CO., ET AL. 

ON WRIT OF CERTIORARI 
TO THE UNITED STATES COURT OF APPEALS 
FOR THE FEDERAL CIRCUIT 

BRIEF FOR THE UNITED STATES 
AS AMICUS CURIAE SUPPORTING VACATUR 
AND REMAND 

JAMES A. TOUPIN 

General Counsel 

JOHN M. WHEALAN 

Solicitor 

LINDA MONCYS ISACSON 
CYNTHIA C. LYNCH 
MARK NAGUMO 

Associate Solicitors 
United States Patent and 

Trademark Office 
Arlington, VA 22215 
THEODORE B. OLSON 
Solicitor General 

Counsel of Record 

STUART E. SCHIFFER 

Acting Assistant Attorney 

General 

LAWRENCE G. WALLACE 

Deputy Solicitor General 

JEFFREY P. MINEAR 

Assistant to the Solicitor 

General 

VITO J. DIPIETRO 
ANTHONY J. STEINMEYER 
JOHN FARGO 
HOWARD S. SCHER 
GRACE KARAFFA 

Attorneys 

Department of Justice 
Washington, D.C. 20530-0001 
(202) 514–2217 

QUESTIONS PRESENTED 

The doctrine of equivalents provides that a product 
or process that does not literally infringe upon the 
express terms of a patent claim may nevertheless be 
found to infringe if there is an “equivalence” between 
the elements of the accused product or process and the 
claimed elements of the patented invention. Warner- 
Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 
21 (1997). That doctrine is limited by the concept of 
prosecution history estoppel, which recognizes that, if a 
patent claim is amended during patent prosecution, the 
amendment may curtail application of the doctrine of 
equivalents to the amended claim. See id. at 30-34. The 
questions presented in this case are: 

1. Whether an amendment of a patent claim that 
narrows the scope of the claim for any reason related to 
the statutory requirements for a patent gives rise to 
prosecution history estoppel with respect to the 
amended portion of the claim. 

2. Whether an amendment of a patent claim that 
gives rise to prosecution history estoppel completely 
precludes invocation of the doctrine of equivalents for 
the amended portion of the claim. 

(I) 

TABLE OF CONTENTS 

Page 

Interest of the United States ...................................................... 
1 

Statement ........................................................................................ 2 

A. The doctrine of equivalents and the concept of 

prosecution history estoppel ......................................... 
3 

B. The relevant facts ............................................................. 
5 

C. The pertinent proceedings .............................................. 
7 

Summary of argument .................................................................. 
9 

Argument: 

The court of appeals correctly ruled that a patent 

claim amendment that narrows the scope of a claim 

gives rise to prosecution history estoppel, but the 

court erred in holding that prosecution history 

estoppel completely precludes application of the 

doctrine of equivalents ......................................................... 

11 

A. An amendment of a patent claim that narrows 

the scope of a claim for reasons related to the 

statutory requirements for a patent gives rise to 

prosecution history estoppel with respect to the 

amended portion of the claim ....................................... 

13 

B. An amendment of a patent claim that gives rise 

to prosecution history estoppel presumptively 

precludes invocation of the doctrine of equiva- 
lents for the amended portion of the claim ................ 

17 

C. The court of appeals’ judgment should be va- 
cated and the case should be remanded to the dis- 
trict court for further proceedings .............................. 
28 

Conclusion ....................................................................................... 30 

TABLE OF AUTHORITIES 

Cases: 

ACLARA Biosciences, Inc. v. Caliper Techs. Corp., 

125 F. Supp. 2d 391 (N.D. Cal. 2000) .................................. 25 

(III) 

IV 

Cases—Continued: Page 

Crawford v. Heysinger, 123 U.S. 589 (1887) ..................... 

14 

Cybor Corp. v. FAS Techs., Inc., 138 F.3d 1448 

(Fed. Cir. 1998) ....................................................................... 

15 

Exhibit Supply Co. v. Ace Patents Corp., 315 U.S. 

126 (1942) .............................................................. 

4, 14, 15, 24, 25 

Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki 

Co., 187 F.3d 1381 (Fed. Cir. 1999) .................................... 

2 

Goodyear Dental Vulcanite Co. v. Davis, 102 U.S. 

222 (1880) ................................................................................. 

22 

Graco Children’s Prods., Inc. v. Regalo Int’l, LLC, 

No. 97-CV-6885, 2001 WL 392886 (E.D. Pa. Apr. 17, 

2001) ......................................................................................... 16 

Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 

339 U.S. 605 (1950) .............................................................. 

3, 26 

Hester Indus., Inc. v. Stein, Inc., 142 F.3d 1472 

(Fed. Cir.), cert. denied, 525 U.S. 947 (1998) .................... 

17 

Honeywell Int’l Inc. v. Hamilton Sundstrand Corp., 

No. Civ. A 99-309 GMS, 2001 WL 66348 (D. Del. 

Jan. 8, 2001) ............................................................................. 

16 

Hughes Aircraft Co. v. United States: 

717 F.2d 1351 (Fed. Cir. 1983) ............................................. 

18 

140 F.3d 1470, reh’g denied over dissents, 148 F.3d 

1384 (Fed. Cir. 1998), cert. denied, 525 U.S. 1177 

(1999) ................................................................................... 19 

Hurlbut v. Schillinger, 130 U.S. 456 (1889) ...................... 

22 

Keystone Driller Co. v. Northwest Eng’g Corp., 

294 U.S. 42 (1935) ................................................................... 

14 

Kinzenbaw v. Deere & Co., 741 F.2d 383 (Fed. Cir. 

1984), cert. denied, 470 U.S. 1004 (1985) ........................... 

18 

Leggett v. Avery, 101 U.S. 256 (1880) ................................. 

17 

Litton Sys., Inc. v. Honeywell Inc., 238 F.3d 1376 

(Fed. Cir.), petition for cert. pending, 

No. 00-1617 (filed Apr. 23, 2001) ......................................... 

16 

Lockheed Martin Corp. v. Space Sys./Loral, Inc., 

249 F.3d 1314 (Fed. Cir. 2001) ............................................. 16 

V 

Cases—Continued: Page 

Markman v. Westview Instruments, Inc., 517 U.S. 

370 (1996) ................................................................................. 

27 

McClain v. Ortmayer, 141 U.S. 419 (1891) ....................... 

23 

Merrill v. Yeomans, 94 U.S. 568 (1877) ............................. 

23 

Pickholtz v. Rainbow Techs., Inc., 125 F. Supp. 2d 

1156 (N.D. Cal. 2000) ............................................................. 

16 

Royal Typewriter Co. v. Remington Rand, Inc., 

168 F.2d 691 (2d Cir.), cert. denied, 335 U.S. 825 

(1948) ........................................................................................ 26 

Schriber-Schroth Co. v. Cleveland Trust Co., 311 

U.S. 211 (1940) ........................................................................ 

4 

Seattle Box Co. v. Industrial Crating & Packing, 

Inc., 731 F.2d 818 (Fed. Cir. 1984) ..................................... 

17 

Shoketsu Kinzoku Kogyo Kabushiki Co. v. Festo 

Corp.: 

520 U.S. 1111 (1997) .......................................................... 

2 

187 F.3d 1381 (Fed. Cir. 1999) ........................................ 

2 

Smith v. Magic City Kennel Club, Inc., 282 U.S. 

784 (1931) ................................................................................. 

14 

SRAM Corp. v. AD-II Eng’g, Inc., No. 00 C 

6675, 2001 WL 817857 (N.D. Ill. July 9, 2001) .................. 

16 

TM Patents, LLP v. IBM Corp., 136 F. Supp. 2d 

209 (S.D.N.Y. 2001) ............................................................... 

16 

Turbocare Div. v. General Elec. Co., No. 00-1349 

(Fed. Cir. Aug. 29, 2001) ..................................................... 

15-16 

United States v. Hughes Aircraft Co., 525 U.S. 

1177 (1999) ............................................................................... 

19 

Vitronics Corp. v. Conceptronic, Inc., 90 F.3d 1576 

(Fed. Cir. 1996) ....................................................................... 

23 

Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 

520 U.S. 17 (1997) ............................................................. 

passim 

Zletz, In re, 893 F.2d 319 (Fed. Cir. 1989) ........................... 21 

VI 

Constitution and statutes: 

Page 

U.S. Const. Art. I, § 8, Cl. 8 (Patent Clause) ....................... 
1 

35 U.S.C. 112 ...................................................................... 
6, 11, 23 

35 U.S.C. 131 (1994 & Supp. V 1999) ..................................... 
1 

35 U.S.C. 252 (1994 & Supp. V 1999) ..................................... 
17 

Miscellaneous: 

Donald Chisum, The Scope Of Protection For Patents 

After The Supreme Cour’ts Warner-Jenkinson Deci- 
sion: The Fair Protection-Certainty Conundrum, 
14 Santa Clara Computer & High Tech. L.J. 1 
(1998) ........................................................................................ 13 

In the Supreme Court of the United States 

No. 00-1543 

FESTO CORPORATION, PETITIONER 

v. 

SHOKETSU KINZOKU KOGYO KABUSHIKI CO., ET AL. 

ON WRIT OF CERTIORARI 
TO THE UNITED STATES COURT OF APPEALS 
FOR THE FEDERAL CIRCUIT 

BRIEF FOR THE UNITED STATES 
AS AMICUS CURIAE SUPPORTING VACATUR 
AND REMAND 

INTEREST OF THE UNITED STATES 

Pursuant to the Patent Clause of the Constitution, 
U.S. Const. Art. I, § 8, Cl. 8, Congress has charged the 
United States Patent and Trademark Office (PTO), an 
agency of the Department of Commerce, with respon- 
sibility for examining all patent applications to ensure 
that they satisfy the statutory conditions for patent- 
ability. See 35 U.S.C. 131 (1994 & Supp. V 1999). In 
addition, the United States is regularly engaged in 
litigation over the validity and scope of patents, as a 
patent holder and as a defendant in infringement 
actions. The United States accordingly has a strong 
interest, embracing a number of perspectives, in a 
stable, predictable, and efficient patent system. The 
United States has a particular interest in ensuring that 

(1) 

2 

the doctrine of equivalents and the related concept of 
prosecution history estoppel provide both a fair scope of 
patent protection and sufficient certainty of a patent’s 
limits to protect legitimate expectations while promot- 
ing competition and innovation. 

STATEMENT 

Petitioner Festo Corporation commenced a civil 
action in the United States District Court for the 
District of Massachusetts alleging that respondents had 
infringed two United States patents that Festo owns. 
Festo asserted, among other theories, infringement 
under the doctrine of equivalents. See Pet. App. 3a. 
The district court concluded that respondents had in- 
fringed the patents, id. at 208a-209a, and the United 
States Court of Appeals for the Federal Circuit 
affirmed the district court’s judgment, id. at 190a-207a. 
This Court vacated the court of appeals’ judgment and 
remanded the case for further consideration in light of 
its decision in Warner-Jenkinson Co. v. Hilton Davis 
Chemical Co., 520 U.S. 17 (1997). See Shoketsu Kin- 
zoku Kogyo Kabushiki Co. v. Festo Corp., 520 U.S. 1111 
(1997). 

On remand, the court of appeals affirmed the district 
court’s judgment in part and vacated and remanded in 
part. Pet. App. 156a-189a. The court of appeals then 
granted a petition for rehearing en banc before 12 
judges of that court on five specific issues relating to 
the doctrine of equivalents and the concept of prosecu- 
tion history estoppel. Festo Corp. v. Shoketsu Kinzoku 
Kogyo Kabushiki Co., 187 F.3d 1381 (Fed. Cir. 1999). 
Based on its resolution of those issues, the en banc 
court reversed the district court’s judgment of infringe- 
ment. Pet. App. 1a-56a. Six of the court of appeals 
judges wrote separately. See id. at 56a-64a (Plager, J., 

3 

concurring); id. at 64a-69a (Lourie, J., concurring); id. at 
69a-111a (Michel, J., concurring in part and dissenting 
in part); id. at 111a-113a (Rader, J., concurring in part 
and dissenting in part); id. at 113a-131a (Linn, J., 
concurring in part and dissenting in part); id. at 131a- 
155a (Newman, J., concurring in part and dissenting in 
part). 

A. The Doctrine Of Equivalents And The Concept Of 

Prosecution History Estoppel 

This Court’s decision in Warner-Jenkinson sets out 
the central principles that govern the doctrine of 
equivalents. “Under this doctrine, a product or process 
that does not literally infringe upon the express terms 
of a patent claim may nonetheless be found to infringe if 
there is ‘equivalence’ between the elements of the 
accused product or process and the claimed elements of 
the patented invention.” 520 U.S. at 21. “What con- 
stitutes equivalency must be determined against the 
context of the patent, the prior art, and the particular 
circumstances of the case.” Id. at 24 (quoting also 
Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 
U.S. 605, 609 (1950)). 

The Court expressed concern in Warner-Jenkinson 
that the doctrine of equivalents, as it had come to be 
applied before that decision, had “taken on a life of its 
own, unbounded by the patent claims.” 520 U.S. at 28- 

29. The Court observed that unbridled application of 
the doctrine conflicts with “the definitional and public- 
notice functions of the statutory claiming requirement.” 
Id. at 29. It responded to that conflict by making clear 
that “[e]ach element contained in a patent claim is 
deemed material to defining the scope of the patented 
invention, and thus the doctrine of equivalents must be 
applied to individual elements of the claim, not to the 

4 

invention as a whole.” Ibid. Furthermore, the Court 
emphasized that “[i]t is important to ensure that the 
application of the doctrine, even as to an individual 
element, is not allowed such broad play as to effectively 
eliminate that element in its entirety.” Ibid. 

The Court additionally recognized that the doctrine 
of equivalents is constrained by “a well-established 
limit on nonliteral infringement, known variously as 
‘prosecution history estoppel’ and ‘file wrapper estop- 
pel.’ ” Warner-Jenkinson, 520 U.S. at 30. That concept 
rests on the understanding that, if a patent applicant 
narrows the scope of patent protection by claim 
amendments or other actions during the proceedings 
before the PTO to obtain a patent, the patent holder 
should not be allowed to argue, in a subsequent in- 
fringement action, that the disclaimed subject matter is 
equivalent to that which the applicant had actually 
claimed in its narrowing amendment. See id. at 30-34; 
Schriber-Schroth Co. v. Cleveland Trust Co., 311 U.S. 
211, 220-221 (1940). 

The Court noted that prosecution history estoppel 
most frequently comes into play when the applicant, in 
order to overcome a PTO patent examiner’s rejections 
based on references to the prior art, narrows a portion 
of the applicant’s original claim and thereby effectively 
disavows that the subject matter excluded by the 
narrower claim is equivalent to that claim. See 520 U.S. 
at 31 & n.5 (citing Exhibit Supply Co. v. Ace Patents 
Corp., 315 U.S. 126 (1942), and other examples). But not 
every amendment gives rise to prosecution history 
estoppel. “Where the reason for the change was not 
related to avoiding the prior art, the change may intro- 
duce a new element, but it does not necessarily pre- 
clude infringement by equivalents of that element.” Id. 
at 33. The Court “place[d] the burden on the patent 

5 

holder to establish the reason for an amendment 
required during patent prosecution.” Ibid. Where the 
patent holder fails to establish an explanation, a district 
court “should presume that the patent applicant had a 
substantial reason related to patentability for including 
the limiting element added by amendment” and 
“prosecution history estoppel would bar the application 
of the doctrine of equivalents as to that element.” Ibid. 

B. The Relevant Facts 

Festo owns the Stoll and Carroll patents, which dis- 
close magnetic rodless cylinder assemblies. The 
claimed devices employ a piston on the inside of a cylin- 
der, which moves in response to fluid under pressure, 
and a sleeve on the outside of the cylinder, which is 
magnetically coupled to the piston. Pet. App. 33a. The 
magnetic attraction between the sleeve and the piston 
causes the sleeve to follow the piston as it moves along 
the inside of the cylinder, thus enabling the sleeve to 
transport articles on a conveying system. See ibid. 

Claim 1 of the Stoll patent and Claim 9 of the Carroll 
patent describe the relevant features of the devices. 
See Pet. App. 31a-39a. Each of those claims discloses, 
among other elements, a pair of sealing rings on the 
piston, having a lip on only one side, which contain fluid 
flow and exclude impurities. Id. at 34a-35a, 37a. In 
addition, Claim 1 of the Stoll patent discloses a sleeve 
made of a magnetizable material. Id. at 34a. Respon- 
dents’ accused devices differ in two respects. Those 
devices employ a single two-way sealing ring, having a 
lip on both sides, which seals against fluid flow on both 
sides of the ring. Id. at 38a. In addition, the outer 
portion of the sleeve in respondents’ accused devices is 
made of an aluminum alloy, a material that is not 
magnetizable. Id. at 38a-39a. 

6 

Claim 1 of the Stoll patent was amended during 
prosecution. Claim 1 originally recited “[a] linear motor 
for use in a conveying system” that included “a piston 
which is slidable in said tubular part and which has 
sealing means at each end,” and a piston and drive 
assembly “each carrying a drive magnet arrangement 
in the form of a hollow cylindrical assembly.” Pet. App. 
39a. The patent examiner rejected that claim, as well 
as the other claims contained in the Stoll application, 
under 35 U.S.C. 112, because the “exact method of 
operation is unclear.” Pet. App. 40a. The applicant 
amended its claims, reciting, among other things, the 
sealing ring structure and a sleeve of magnetizable 
material. Ibid. The applicant also stated, in accom- 
panying remarks, that the sealing ring structure made 
the amended claims distinguishable from prior art 
references that the patent examiner had identified as 
possibly pertinent. Id. at 40a-41a. The patent exam- 
iner allowed the amended claims. Id. at 41a. 

Claim 9 of the Carroll patent was also amended dur- 
ing patent prosecution, during a reexamination pro- 
ceeding. Claim 1 of the original Carroll patent did not 
recite sealing rings, but disclosed them in the written 
description portion of the specification. Pet. App. 42a. 
The applicant thereafter submitted the patent for 
reexamination in light of a German prior art reference 
that disclosed a similar device having several of the 
claimed features, including a pair of sealing rings. Ibid. 
During the reexamination proceeding, the applicant 
canceled Claim 1 and added Claim 9, which explicitly 
recited a sealing ring structure that, according to the 
applicant, was distinguishable from the prior art. Id. at 
42a-43a. The patent examiner allowed the amended 
claim. Id. at 43a. 

7 

C. The Pertinent Proceedings 

The district court granted Festo summary judgment 
on the ground that respondents’ devices infringed upon 
the Carroll patent under the doctrine of equivalents. 
Pet. App. 43a-44a. The district court found that respon- 
dents had failed to come forward with material evi- 
dence rebutting Festo’s expert testimony that the 
single two-way sealing ring that respondents employed 
in their devices was equivalent to the two sealing rings 
recited in the Carroll patent. Id. at 44a. Respondents 
did not argue that prosecution history estoppel applied 
to the Carroll patent, id. at 53a n.8, but they did raise 
that defense on summary judgment in response to 
Festo’s argument that respondents’ devices infringed 
upon the Stoll patent, id. at 43a-44a. The district court 
rejected the defense, and Festo’s assertion that 
respondents infringed upon the Stoll patent was tried 
before a jury. Id. at 44a. The jury found, through a 
special verdict, that respondents’ devices infringed 
upon the Stoll patent under the doctrine of equivalents. 
Id. at 44a-45a. 

The court of appeals initially affirmed the district 
court judgment. Pet. App. 190a-211a. On remand 
following this Court’s decision in Warner-Jenkinson, 
the court of appeals affirmed in part. Id. at 156a-189a. 
The en banc court ultimately reversed the district 
court’s decision in its entirety. Id. at 1a-56a. The court 
decided the appeal by addressing five questions 
“relating to the doctrine of equivalents that remained in 
the wake of ” Warner Jenkinson, see id. at 2a-4a, 8a- 
32a, and then applying its legal determinations to the 
relevant facts, id. at 4a, 45a-56a. 

The court concluded in response to Question 1 that an 
amendment of a patent claim that narrows the scope of 

8 

a claim for any reason related to the statutory 
requirements for a patent will give rise to prosecution 
history estoppel with respect to the amended portion of 
the claim. Pet. App. 3a, 8a-11a. The court determined 
in response to Question 2 that a “voluntary” claim 
amendment can trigger prosecution history estoppel 
and should be treated the same as claim amendments 
made in response to a patent examiner’s rejection. Id. 
at 3a-4a, 11a-13a. In response to Question 3, the court 
concluded that, when a claim amendment gives rise to 
prosecution history estoppel, the amendment acts as a 
“complete bar” and precludes any invocation of the 
doctrine of equivalents for the amended portion of the 
claim. Id. at 4a, 13a-30a. In response to Question 4, the 
court ruled that “unexplained” amendments likewise 
are not entitled to any range of equivalents. Id. at 4a, 
31a. The court declined to decide Question 5, which 
asked whether a judgment of infringement in this case 
would violate the “all elements” rule established in 
Warner-Jenkinson, because its resolution of the prior 
questions, when applied to the facts of this case, 
rendered the question moot. Id. at 4a, 31a-32a. 

The court of appeals applied its legal determinations 
to the facts of this case and concluded that those deter- 
minations mandated reversal of the district court’s 
decision. See Pet. App. 45a-56a. The court ruled that, 
because the relevant claim elements of the Stoll and 
Carroll patents were the product of amendments that 
narrowed the claims, and because Festo did not 
establish explanations for those amendments unrelated 
to patentability, the amendments gave rise to prosecu- 
tion history estoppel, which completely bars the appli- 
cation of the doctrine of equivalents to the amended 
portions of those claims. Id. at 56a. Four judges 
dissented in part from that ruling, objecting principally 

9 

to the court’s application of prosecution history 
estoppel as a “complete” bar to invocation of the 
doctrine of equivalents. See id. at 69a-70a (Michel, J.); 
id. at 111a-113a (Rader, J.); id. at 113a-114a (Linn, J.); 
id. at 131a-133a (Newman, J.). 

SUMMARY OF ARGUMENT 

This Court’s decision in Warner-Jenkinson Co. v. 
Hilton Davis Chemical Co., 520 U.S. 17 (1997), de- 
scribes the interplay between the doctrine of equiva- 
lents and prosecution history estoppel. That decision 
makes clear that the doctrine of equivalents plays a 
carefully circumscribed role in determining the scope of 
patent claims and that prosecution history estoppel 
remains an important limitation on the role of that 
doctrine. This case presents two important questions 
respecting prosecution history estoppel that Warner- 
Jenkinson did not expressly answer. They should be 
resolved by reference to that decision and its recogni- 
tion of the central balance that must be struck between 
the public’s need for clarity of patent coverage and the 
patent holder’s need for fair protection from infringe- 
ment. 

A. The court of appeals correctly ruled that an 
amendment of a patent claim that narrows the scope of 
the claim for reasons of patentability gives rise to 
prosecution history estoppel with respect to the 
amended portion of that claim. That result follows from 
this Court’s decision in Warner-Jenkinson, which 
reaffirmed the longstanding principle that a patent 
applicant who narrows the initial claims and effectively 
surrenders subject matter as a condition for obtaining a 
patent implicitly disclaims any right to a patent for the 
subject matter that was surrendered. Nevertheless, a 
court must carefully analyze the claim amendment in 

10 

the context of the alleged infringement to ensure that 
the amendment does indeed manifest a narrowing of 
the claim that surrenders relevant subject matter. A 
court should apply prosecution history estoppel only if 
the particular terms of the amendment narrow the 
relevant claim in that manner. 

B. The court of appeals erred in ruling that a patent 
claim amendment that gives rise to prosecution history 
estoppel completely bars invocation of the doctrine of 
equivalents for the amended portion of the claim. The 
court concluded that its prior approach to prosecution 
history estoppel, which applied a “flexible bar,” was 
unworkable because it did not provide certainty with 
respect to the scope of patent protection. While that 
prior approach was unsatisfactory, the court’s “com- 
plete bar” does not comport with this Court’s measured 
perspective in Warner-Jenkinson and fails to strike a 
sound balance between certainty of patent scope and 
fair protection of patent rights. In keeping with its 
approach in Warner-Jenkinson, this Court should hold 
the patent holder subject to a presumption that nar- 
rowing amendments preserved no range of equivalents. 
The patent holder could overcome that presumption by 
showing a concrete basis, based on the patent prosecu- 
tion record and relevant to the specific context of the 
infringement suit, for extending the amended portion of 
the claim beyond its literal terms to encompass equiva- 
lent elements. That approach would substantially 
diminish the unacceptably high level of uncertainty that 
presently inheres in the application of prosecution 
history estoppel while fairly protecting the interests of 
patent holders. 

C. Because the court of appeals erred in ruling that 
prosecution history estoppel completely bars the doc- 
trine of equivalents for amended claims, the court’s 

11 

judgment should be vacated and the case remanded for 
further proceedings. The court of appeals should re- 
mand the case to the district court for a determination 
of whether the patent claims were narrowed in a way 
that would lead to prosecution history estoppel. If so, 
the court should place the burden on the patent holder 
to overcome the presumption that the literal terms of 
the relevant claim elements describe the full scope of 
the patents. 

ARGUMENT 

THE COURT OF APPEALS CORRECTLY RULED 
THAT A PATENT CLAIM AMENDMENT THAT NAR- 
ROWS THE SCOPE OF A CLAIM GIVES RISE TO 
PROSECUTION HISTORY ESTOPPEL, BUT THE 
COURT ERRED IN HOLDING THAT PROSECUTION 
HISTORY ESTOPPEL COMPLETELY PRECLUDES 
APPLICATION OF THE DOCTRINE OF EQUIVA- 
LENTS 

This Court’s decision in Warner-Jenkinson Co. v. 
Hilton Davis Chemical Co., 520 U.S. 17 (1997), has 
greatly clarified the role of the doctrine of equivalents 
in patent infringement suits. The Court has made clear 
that the scope of a patent is controlled primarily by the 
“statutory claiming requirement” of the patent laws, 
see 35 U.S.C. 112, which requires the patent applicant 
to set out with precision the claim limitations that 
define the scope of the invention. See 520 U.S. at 28-30. 
The patent claims, which serve both “definitional and 
public-notice” functions, id. at 29, establish the critical 
dimensions of a patent’s protection. The doctrine of 
equivalents plays a strictly confined role in ascertaining 
those dimensions in response to a claim of infringement. 
The doctrine—which takes into account that the limits 
of language may result in unavoidably imprecise patent 

12 

claims and that the patent owner is entitled to pro- 
tection from infringement by products that differ only 
through insubstantial deviations from the patent’s 
verbal formulation—provides the patent holder with a 
limited measure of protection beyond the patent’s 
literal terms. See id. at 28-29, 40. 

Warner-Jenkinson has also clarified the relationship 
between the doctrine of equivalents and the concept of 
prosecution history estoppel. Prosecution history 
estoppel, a judge-made principle that recognizes that 
patent claim amendments frequently result in a dimin- 
ishment of the patent’s scope, remains an important 
limitation on the doctrine of equivalents. 520 U.S. at 30, 
33-34. But the Court made clear that the reason for the 
amendment is central to the estoppel analysis. Id. at 
30-31, 32. “Mindful that claims do indeed serve both a 
definitional and a notice function,” the Court “place[d] 
the burden on the patent holder to establish the reason 
for an amendment required during patent prosecution.” 
Id. at 33. If the patent holder fails to come forward 
with a reason for amending an element of the claim, 
then the district court “should presume that the patent 
applicant had a substantial reason related to patentabil- 
ity for including the limiting element” and “prosecution 
history estoppel would bar the application of the 
doctrine of equivalents as to that element.” Ibid. 

This case presents two questions that Warner-Jen- 
kinson did not explicitly decide: (1) whether an amend- 
ment of a patent claim that narrows the scope of the 
claim for any reason related to the statutory require- 
ments for a patent gives rise to prosecution history 
estoppel with respect to the amended portion of the 
claim; and (2) whether a patent claim amendment that 
gives rise to prosecution history estoppel completely 
precludes invocation of the doctrine of equivalents for 

13 

the amended portion of the claim. The en banc court of 
appeals answered each of those questions affirmatively. 

We submit that the starting point of the analysis 
should be Warner-Jenkinson, which marks this Court’s 
baseline for ascertaining the relationship between the 
doctrine of equivalents and prosecution history 
estoppel. That decision recognizes the continued vital- 
ity of a properly limited doctrine of equivalents, 520 
U.S. at 21, but emphasizes the “definitional and public- 
notice functions of the statutory claiming requirement,” 
id. at 29, and the important role that the PTO’s patent 
prosecution process plays in ensuring that the patent 
claims are stated with precision and limited to properly 
patentable subject matter, id. at 33-34. The analysis 
should take account of the central tension in patent law 
between the public’s need for clarity of patent cover- 
age, both to avoid trespassing on patent holders’ rights 
and to spur innovations, and the patent holder’s need 
for fair protection from infringement by products that 
differ only insubstantially from the patented invention. 
See, e.g., Donald Chisum, The Scope Of Protection For 
Patents After The Supreme Court’s Warner-Jenkinson 
Decision: The Fair Protection-Certainty Conundrum, 
14 Santa Clara Computer & High Tech. L.J. 1 (1998). 

A. An Amendment Of A Patent Claim That Narrows The 

Scope Of A Claim For Reasons Related To The 

Statutory Requirements For A Patent Gives Rise To 

Prosecution History Estoppel With Respect To The 

Amended Portion Of The Claim 

The court of appeals correctly concluded that “a nar- 
rowing amendment made for any reason related to the 
statutory requirements for a patent will give rise to 
prosecution history estoppel with respect to the 
amended claim element.” Pet. App. 9a. The court’s 

14 

ruling is consistent with Warner-Jenkinson and rests 
on familiar principles of patent law. 

1. Warner-Jenkinson rejected the argument that 
“any surrender of subject matter during patent prose- 
cution, regardless of the reason for such surrender, pre- 
cludes recapturing any part of that subject matter, 
even if it is equivalent to the matter expressly claimed.” 
520 U.S. at 30. Rather, a district court faced with an as- 
sertion of prosecution history estoppel in an infringe- 
ment suit must examine “the reason for an amend- 
ment.” Ibid. The Court indicated that prosecution his- 
tory estoppel most commonly arises as a result of 
“amendments made to avoid the prior art,” ibid., a rea- 
son that invariably gives rise to prosecution history 
estoppel. See, e.g., Exhibit Supply Co. v. Ace Patents 
Corp., 315 U.S. 126, 136 (1942); Keystone Driller Co. v. 
Northwest Eng’g Corp., 294 U.S. 42, 48 (1935); Smith v. 
Magic City Kennel Club, Inc., 282 U.S. 784, 789-790 
(1931). The Court further noted that prosecution his- 
tory estoppel also arises from amendments made to ad- 
dress a specific concern “that arguably would have ren- 
dered the claimed subject matter unpatentable.” War- 
ner-Jenkinson, 520 U.S. at 30-31. See Crawford v. 
Heysinger, 123 U.S. 589, 606 (1887) (applying prosecu- 
tion history estoppel to amendments made in response 
to operability rejections).1 

1 The Court relied primarily on its own precedent to reject the 
argument that prosecution history estoppel applies without regard 
to the reason for an amendment. See Warner-Jenkinson, 520 U.S. 
at 30-31 & n.5. But the Court also noted that the focus on pat- 
entability is appropriate in light of patent policy and practice. The 
Court stated that there is “no substantial cause for requiring a 
more rigid rule,” id. at 32, noting that the PTO may have relied 
upon a more “flexible” approach and that altering current practice 
“could very well subvert the various balances the PTO sought to 

15 

That conclusion has compelling force. A patent 
applicant who narrows the initial claims and effectively 
surrenders subject matter as a condition for obtaining a 
patent implicitly disclaims any right to a patent for the 
subject matter that was surrendered. See, e.g., Exhibit 
Supply, 315 U.S. at 136; Cybor Corp. v. FAS Techs., 
Inc., 138 F.3d 1448, 1460 (Fed. Cir. 1998) (en banc). As 
the court of appeals explained, it should not matter 
whether the impetus was a prior art rejection or some 
other patent law requirement. Pet. App. 9a-11a. In 
either situation, the patent applicant, who presumably 
seeks the broadest patent possible, has effectively made 
a public disclaimer of the surrendered subject matter in 
exchange for the patent. Prosecution history estoppel 
simply implements the predictable consequence that 
the applicant’s patent rights are commensurately lim- 
ited. The court of appeals was accordingly correct in 
concluding that a claim amendment gives rise to prose- 
cution history estoppel whenever “the patent applicant 
had a substantial reason related to patentability for 
including the limiting element added by amendment.” 
Warner-Jenkinson, 520 U.S. at 33. 

2. This Court’s decision in Warner-Jenkinson indi- 
cates that discerning analysis is nevertheless necessary 
when applying the court of appeals’ ruling. An amend- 
ment, even one related to patentability, “does not 
necessarily preclude infringement by equivalents of 
that element.” 520 U.S. at 33. As the court of appeals’ 
post-Festo decisions emphasize, a claim amendment 
does not give rise to prosecution history estoppel unless 
it manifests a narrowing of the patent claim that 
surrenders relevant subject matter. See, e.g., Turbo- 

strike when issuing the numerous patents which have not yet 
expired,” id. at 32 n.6. 

16 

care Div. v. General Elec. Co., No. 00-1349 (Fed. Cir. 
Aug. 29, 2001), slip op. 24-25; Lockheed Martin Corp. v. 
Space Sys./Loral, Inc., 249 F.3d 1314, 1326 (Fed. Cir. 
2001); Litton Sys., Inc. v. Honeywell Inc., 238 F.3d 
1376, 1380 (Fed. Cir.), petition for cert. pending, No. 00- 
1617 (filed Apr. 23, 2001).2 

Patent applicants may amend their patent claims for 
reasons of patentability—such as to clarify an ambigu- 
ous term—that do not result in narrowing the claims 
and surrendering subject matter. Rather, the amend- 
ments may state the same—or broader—patent claims 
in more precise terms. For example, an applicant may 
amend by rewriting a dependent claim as an indepen- 
dent claim. See Honeywell Int’l Inc. v. Hamilton 
Sundstrand Corp., No. Civ. A. 99-309 GMS, 2001 WL 
66348, at *6 (D. Del. Jan. 8, 2001) (citing Festo). Such 
amendments do not give rise to prosecution history 
estoppel, which has as its core functions “preserving 
the notice function of the claims and preventing patent 
holders from recapturing under the doctrine of equiva- 

2 See also Graco Children’s Prods., Inc. v. Regalo Int’l, LLC, 
No. 97-CV-6885, 2001 WL 392886, at *3-*4 (E.D. Pa. Apr. 17, 2001) 
(adding language to a claim that merely restated a limitation that 
was already present did not give rise to prosecution history 
estoppel because it did not narrow the scope of the claim); SRAM 
Corp. v. AD-II Eng’g, Inc., No. 00 C 6675, 2001 WL 817857, at *10 
(N.D. Ill. July 9, 2001) (an amendment to the patent specification, 
but not the patent claims, that overcame a rejection for indefinite- 
ness by supplying the antecedent basis for a claim limitation did 
not trigger prosecution history estoppel because it did not narrow 
the scope of the patent claim); see also TM Patents, LLP v. IBM 
Corp., 136 F. Supp. 2d 209, 217 (S.D.N.Y. 2001) (“Festo, by its 
terms, applies only to amendments that narrow the scope of patent 
claims.”); Pickholtz v. Rainbow Techs., Inc., 125 F. Supp. 2d 1156, 
1161 (N.D. Cal. 2000) (“the court must consider whether the 
amendments ‘narrowed the literal scope of the claim’ ”). 

17 

lents subject matter that was surrendered before the 
Patent Office.” Pet. App. 11a. Patent applicants should 
not be deterred by the specter of prosecution history 
estoppel from making amendments that preserve the 
claimed subject matter but state their claims more 
precisely and thereby enhance the notice function of the 
patent claims. Thus, even if a patent claim is amended 
for reasons of patentability, a court should apply 
prosecution history estoppel only if the particular terms 
of the amendment narrow the relevant claim.3 

B. An Amendment Of A Patent Claim That Gives Rise To 

Prosecution History Estoppel Presumptively Precludes 

Invocation Of The Doctrine Of Equivalents For The 

Amended Portion Of The Claim 

The court of appeals’ conclusion that a narrowing 
amendment related to patentability gives rise to 
prosecution history estoppel leads directly to the ques- 

3 Patent law requires a similar inquiry when a patent holder 
seeks reissuance of a patent. See 35 U.S.C. 252 para. 1 (1994 & 
Supp. V 1999); see also Pet. App. 76a-77a (Michel, J., dissenting in 
part). In that situation, the issue is whether a modification of claim 
language in the reissuance application actually changes the sub- 
stantive scope of a claim limitation so as to “recapture” subject 
matter surrendered at the time of the original issuance. See 
Leggett v. Avery, 101 U.S. 256, 260 (1880). The recapture inquiry 
and the question whether a claim amendment gives rise to prose- 
cution history estoppel are analogous in that both look to and de- 
pend upon the same basic inquiry—whether a patentee surren- 
dered subject matter during patent prosecution. See, e.g., Hester 
Indus., Inc. v. Stein, Inc., 142 F.3d 1472, 1480-1483 (Fed. Cir.) 
(comparing the breadth and scope of original and amended claim 
limitations), cert. denied, 525 U.S. 947 (1998); see also Seattle Box 
Co. v. Industrial Crating & Packing, Inc., 731 F.2d 818, 827-828 
(Fed. Cir. 1984) (determining whether reissue claims have the 
same substantive scope as original claims so that there is liability 
for pre-reissue activities). 

18 

tion of what effect the estoppel has in the infringement 
proceeding. The court of appeals concluded, as to that 
question, that “[w]hen a claim amendment creates 
prosecution history estoppel with regard to a claim 
element, there is no range of equivalents available for 
the amended claim element.” Pet. App. 13a-14a. Under 
the court’s ruling, “[a]pplication of the doctrine of 
equivalents to the claim element is completely barred.” 
Id. at 14a. In this respect, it is our view that the court’s 
ruling goes too far. 

1. The court of appeals based its decision to impose a 
“complete bar” largely on “its special expertise” in 
resolving judicially created rules of patent law and 
reconciling conflicts among its own decisions. Pet. App. 
19a, 24a. The court detected two lines of authority 
among its precedents. In its view, decisions such as 
Hughes Aircraft Co. v. United States, 717 F.2d 1351 
(Fed. Cir. 1983), treated prosecution history estoppel as 
imposing a “flexible bar” on the range of equivalents 
“within a spectrum ranging from great to small to 
zero,” id. at 1363. Pet. App. 19a. But, according to the 
court, decisions such as Kinzenbaw v. Deere & Co., 741 
F.2d 383 (Fed. Cir. 1984), cert. denied, 470 U.S. 1004 
(1985), treated prosecution history estoppel as a “com- 
plete bar” that precluded the “speculative inquiry” of 
whether a narrowing amendment has preserved a 
range of equivalents beyond its literal terms, id. at 389. 
Pet. App. 20a-21a. See id. at 21a-24a (discussing com- 
mentary on the allegedly contradictory lines of author- 
ity); but see id. at 91a-93a (Michel, J., dissenting in part) 
(disputing whether there are contradictory lines of 
authority); id. at 129a (Linn, J., dissenting in part) 
(same). 

The court of appeals concluded that the flexible bar 
had proved “unworkable” because it does not provide 

19 

“certainty as to the scope of patent protection.” Pet. 
App. 24a-25a. According to that court, a flexible bar 
leaves the public, the patent holder, and competitors 
unable to predict until completion of the infringement 
suit “where the line of surrender is drawn,” id. at 25a, 
and fails “to enforce the disclaimer effect of a narrowing 
claim amendment,” id. at 26a. A complete bar, by 
contrast, “provides the public and the patentee with 
definite notice as to the scope of the claimed invention,” 
id. at 28a, and allows competitors to improve and 
“design around” the claimed invention “without being 
inhibited by the threat of a lawsuit” from developing 
new innovations, id. at 30a. The court additionally 
noted that a complete bar “reins in the doctrine of 
equivalents” and “reduces the conflict and tension 
between the patent protection afforded by the doctrine 
of equivalents and the public’s ability to ascertain the 
scope of a patent.” Ibid. 

2. The policy concerns that led the court of appeals 
to adopt its “complete bar” are substantial. The United 
States unsuccessfully petitioned for a writ of certiorari 
in Hughes Aircraft Co. v. United States, 140 F.3d 1470, 
reh’g denied over dissents, 148 F.3d 1384 (Fed. Cir. 
1998), cert. denied, 525 U.S. 1177 (1999), after a divided 
court of appeals subjected the government to an 
infringement judgment of more than $100 million based 
on that court’s pre-Festo conception of prosecution 
history estoppel. As explained in that petition, the 
court’s estoppel analysis “failed to recognize what [the 
applicant] had surrendered when amending his patent 
claim in response to prior art.” See Pet. at 16, United 
States v. Hughes Aircraft Co., cert. denied, 525 U.S. 
1177 (1999) (No. 98-871). 

While the court’s pre-Festo practice did not suffi- 
ciently confine the doctrine of equivalents, the court’s 

20 

adoption of a complete-bar rule fails to strike the right 
balance between the public interest in certainty of 
patent scope and the patent holder’s interest in the fair 
protection of the patent right. This Court’s conclusion 
in Warner-Jenkinson that the doctrine of equivalents 
retains vitality necessarily requires that the courts 
make an accommodation between those competing in- 
terests. That decision counsels in favor of imposing 
estoppel more rigorously, but it counsels against apply- 
ing prosecution history estoppel as a rigid and poten- 
tially unfair rule that would completely preclude resort 
to the doctrine of equivalents for amended patent 
claims. 

First, Warner-Jenkinson indicates that a primary 
constraint on the doctrine of equivalents should involve 
analytic discipline by the courts when conducting the 
fact-specific inquiry into whether two products or 
processes are equivalent. See 520 U.S. at 28-29. The 
Court adopted the all-elements test for precisely that 
reason, id. at 29, and it further emphasized that the 
“focus on individual elements and a special vigilance 
against allowing the concept of equivalence to eliminate 
completely any such elements” are the appropriate 
means for confining the doctrine to its proper sphere, 
id. at 40. In effect, Warner-Jenkinson directs lower 
courts to construe equivalents as narrowly as neces- 
sary, on a case-by-case basis, to preserve “the defini- 
tional and public-notice functions of the statutory 
claiming requirement.” Id. at 29; see also id. at 29-30. 

Second, Warner-Jenkinson refused to adopt a simi- 
larly “rigid” rule for assessing prosecution history 
estoppel, notwithstanding the clarity such a rule might 
impart, because it would have the effect of substantially 
undermining the stability of the PTO’s patent prosecu- 
tion process. See 520 U.S. at 32 & n.6. The “complete 

21 

bar” rule would have a similar effect. The holders of 
the “numerous patents which have not yet expired,” id. 
at 32 n.6—most of which contain amended claims—are 
properly charged with knowledge that narrowing 
amendments would give rise to prosecution history 
estoppel, but they could not have anticipated that those 
amendments would necessarily result in an absolute bar 
to any range of equivalents. See Pet. App. 110a 
(Michel, J., dissenting in part); id. at 113a (Linn, J., dis- 
senting in part). At the same time, current and future 
applicants could be rendered reluctant to amend claims 
in pending applications for fear of eliminating protec- 
tion against equivalents. That consequence would not 
only discourage the give-and-take between the PTO 
patent examiners and applicants that leads to more 
refined claims, see In re Zletz, 893 F.2d 319, 322 (Fed. 
Cir. 1989), but it would also substantially diminish the 
future effectiveness of the court’s complete bar in 
“rein[ing] in the doctrine of equivalents,” Pet. App. 30a. 
See id. at 108a-110a (Michel, J., dissenting in part); id. 
at 120a-121a (Linn, J., dissenting in part). Hence, the 
disadvantages that the Court in Warner-Jenkinson 
discerned with a “rigid rule” are also present here. 
There is, in short, a logical limit to how much baggage 
the question whether or not there has been an amend- 
ment can be expected to carry in preventing the doc- 
trine of equivalents from “tak[ing] on a life of its own.” 
Warner-Jenkinson, 520 U.S. at 28-29. 

Third, Warner-Jenkinson makes clear that the con- 
cept of prosecution history estoppel, even when applied 
in the most common context of determining the effect of 
amendments designed to avoid prior art, may require 
some inquiry into the record to determine what range 
of equivalents is precluded. The Court specifically 
pointed out that, in the case of such amendments, a 

22 

court may permissibly consider “the manner in which 
the amendment addressed and avoided the objection.” 
520 U.S. at 33 n.7. This Court’s past decisions likewise 
acknowledge the relevance of such an inquiry. See Pet. 
App. 78a-84a (Michel, J., dissenting in part) (discussing 
Goodyear Dental Vulcanite Co. v. Davis, 102 U.S. 222 
(1880), and Hurlbut v. Schillinger, 130 U.S. 456 (1889)). 
The court of appeals’ holding that a narrowing amend- 
ment related to patentability completely bars any 
equivalents would make that inquiry unnecessary. 

3. This Court’s decision in Warner-Jenkinson pro- 
vides guidance on how to resolve the basic tension, 
common to the doctrine of equivalents and prosecution 
history estoppel, between the public’s interest in 
certainty and the patent holder’s interest in a fair scope 
of protection. That decision recognized the value of 
regulating the use of prosecution history estoppel 
through burdens of proof and presumptions that 
accurately reflect the consequences that patent holders 
and competitors should reasonably expect to result 
from claim amendment. See 520 U.S. at 33. The Court 
can likewise use those constructs to formulate a proper 
role for prosecution history estoppel that promotes the 
patent law’s goal of providing certainty, without 
imposing an unduly rigid, and potentially draconian, 
rule. 

In Warner-Jenkinson, the Court concluded that the 
patent holder bears the burden of “establish[ing] the 
reason for an amendment required during patent prose- 
cution.” 520 U.S. at 33. If the patent holder fails to 
establish the reason, the district court “should presume 
that the patent applicant had a substantial reason 
related to patentability” that “would bar the application 
of the doctrine of equivalents.” Ibid. In this case, the 
Court can place a comparable burden on the patent 

23 

holder to demonstrate that the applicant’s narrowing 
amendments preserved a range of equivalents that 
provide a basis for asserting infringement. In the 
absence of a concrete showing, based on the patent 
prosecution record and relevant to the specific context 
of the infringement suit, the district court should 
presume that, when the applicant narrowed its claims 
to obtain a patent, it limited those claims to their literal 
terms.4 

The patent holder rightly should bear the burden of 
demonstrating that the claim amendments preserve the 
type of equivalents at issue because the patent laws 
themselves require the patent applicant to define 
claims with specificity, 35 U.S.C. 112, “not only to 
secure to him all to which he is entitled, but to apprise 
the public of what is still open to them.” McClain v. 
Ortmayer, 141 U.S. 419, 424 (1891). It is “just and fair, 
both to the patentee and to the public,” to expect that 
the patentee will “understand, and correctly describe, 
just what he has invented, and for what he claims a 
patent.” Merrill v. Yeomans, 94 U.S. 568, 573-574 
(1877). When a patent applicant is faced with a rejec- 
tion, the conscientious applicant will focus attention on 
the precise consequences of a narrowing amendment. In 
that situation, the applicant, who “is master of his 

4 This showing should focus on specific facts drawn from the 
intrinsic evidence reflected in the patent prosecution or the spe- 
cific technology involved that would lead one of ordinary skill in 
the art at the time of the amendment to conclude that the asserted 
equivalent was not fairly within the subject matter surrendered. 
Extrinsic evidence, such as expert testimony, might be used to 
explain but not to contradict such intrinsic evidence. Cf. Vitronics 
Corp. v. Conceptronic, Inc., 90 F.3d 1576, 1582-1583 (Fed. Cir. 
1996) (recognizing that extrinsic evidence may not be used to 
derogate from public record in construing patent claims). 

24 

claims,” Pet. App. 67a (Lourie, J., concurring), can be 
expected to give especially fastidious attention to 
carefully defining the scope of the amended claim. It is 
accordingly “just and fair” to place the burden on the 
patent holder to demonstrate that the claim amend- 
ments preserve the type of equivalents at issue in the 
infringement suit. 

It is also “just and fair” to establish a presumption 
that the narrowing amendment states the exact limits 
of the patent claim. When a patent applicant is faced 
with a rejection, the applicant has a particularly 
powerful incentive to frame its narrowing amendment 
as expansively as possible and to avoid surrendering 
any more subject matter than necessary to secure the 
patent. Indeed, the Court has stated that, when a 
patent applicant submits a narrowing amendment to 
avoid prior art, the applicant by necessary implication 
disclaims the range of equivalents that falls between 
the original and the amended claims. See, e.g., Exhibit 
Supply, 315 U.S. at 136. Thus, patent holders have long 
been on notice that they cannot assume, without 
considerable risk, that a narrowing amendment, made 
to overcome a patentability rejection, will embrace 
more than its literal terms. They must correspondingly 
draft their amendments with care. 

The proposed presumption would preserve the full 
literal scope of the amended claim. A patent applicant 
who has made a narrowing amendment related to 
patentability can continue to claim infringement by a 
device that includes, for the amended element, a new 
element that falls outside of what the amendment 
surrendered. As this Court recognized in Exhibit Sup- 
ply, a patent applicant that narrows claims in response 
to a prior art rejection “recognize[s] and emphasize[s] 
the difference between the [original language and the 

25 

amended language] and proclaim[s] his abandonment of 
all that is embraced in that difference.” 315 U.S. at 136 
(emphasis added). Hence, an applicant who wishes to 
describe a means for joining two pieces of wood, but 
wishes to avoid prior art disclosing glue and wooden 
pegs, might use the term “metal fasteners”—rather 
than “screws” or “nails”—to ensure literal coverage of 
the full range of metal fastening devices. An applicant 
does not surrender subject matter, including alterna- 
tive means for accomplishing the same result, that 
careful drafting has preserved. See, e.g., ACLARA 
Biosciences, Inc. v. Caliper Techs. Corp., 125 F. Supp. 
2d 391, 400-403 (N.D. Cal. 2000). 

But the presumption would require the patent holder 
to show a concrete basis, based on the patent prosecu- 
tion record and relevant to the specific context of the 
infringement suit, for a non-literal extension of a claim 
element that was narrowed to obtain a patent. This 
approach would have the advantage of promoting the 
certainty of scope that the court of appeals found 
lacking under its “flexible bar” jurisprudence. See Pet. 
App. 28a-30a. At the same time, it would prevent the 
injustice that could result from imposing a complete bar 
in certain exceptional situations where the preclusion of 
all equivalents would deny a patent holder a fair scope 
of protection. Two such situations are apparent. 

First, a patent holder should be allowed to assert 
that an accused device infringes under the doctrine of 
equivalents if the court finds that the assertedly 
equivalent element is itself an innovation that was not 
known to persons of ordinary skill in the art at the time 
the applicant amended the claim. Prosecution history 
estoppel rests on the rationale that the applicant’s claim 
amendment manifests a surrender of subject matter. 
But the applicant should not be charged with such a 

26 

surrender if the equivalent supposedly surrendered did 
not exist and was not reasonably within the contempla- 
tion of the PTO and the applicant at the time of the 
claim amendment. Rather, the patent holder should 
have the opportunity to establish that use of an 
innovation satisfies the conditions for equivalence. See 
Pet. App. 111a-113a (Rader, J., dissenting in part); cf. 
Warner-Jenkinson, 520 U.S. at 37 (“the proper time for 
evaluating equivalency—and thus knowledge of inter- 
changeability between elements—is at the time of 
infringement, not at the time the patent was issued”). 

Second, a patent holder should be entitled to assert 
that an accused device infringes under the doctrine of 
equivalents if the court concludes that, owing to the 
nature of the subject matter at issue, it was not possible 
for one of ordinary skill in the art to draft a claim 
amendment that literally encompassed the allegedly 
equivalent element while disclaiming the surrendered 
subject matter. The doctrine of equivalents arose from 
concerns that the “unsparing logic” of literalism can 
deny the patent holder fair patent protection. Royal 
Typewriter Co. v. Remington Rand, Inc., 168 F.2d 691, 
692 (2d Cir.) (L. Hand, J.), cert. denied, 335 U.S. 825 
(1948). The courts can properly insist that prosecution 
history estoppel requires applicants to draft claim 
amendments to encompass literally all the equivalents 
they wish to include. But there may be some instances 
in which the literal terms cannot reasonably describe all 
of the insubstantial substitutes that might be conceived 
for a particular element. In those instances, the doc- 
trine of equivalents should be available to protect the 
patent holder from trivial or manifestly insubstantial 
changes that unambiguously deny the inventor “the 
benefit of his invention.” Graver Tank & Mfg. Co. v. 
Linde Air Prods. Co., 339 U.S. 605, 607 (1950). 

27 

The courts should exercise discipline in assessing 
assertions from patent holders that claim amendments 
could not have been crafted with greater precision, lest 
they invite wholesale return to the court of appeals’ 
“flexible bar approach,” which that court properly 
concluded is “unworkable.” Pet. App. 25a. That inquiry 
should proceed as a matter of law. See Markman v. 
Westview Instruments, Inc., 517 U.S. 370 (1996) (courts, 
rather than juries, construe patent claims). It is not 
likely to be burdensome because the courts have a 
ready benchmark for evaluating such claims. A court 
can compare the actual claim amendment against the 
alternative claim formulations that a person of ordinary 
skill in the art could have adopted to provide literal 
coverage of the alleged equivalent. Given the versatil- 
ity of language, patent holders will face a substantial 
obstacle in overcoming the presumption that their 
narrowed claims encompass no more than they literally 
embrace. But that challenge would not be insurmount- 
able if the technology is complex or the alleged dis- 
tinctions are trivial. See Pet. App. 107a-108a (Michel, 
J., dissenting in part) (noting that certain fields, such as 
biotechnology, place particular demands on literalism in 
describing the scope of a claim). 

Creating a presumption, rather than a complete bar, 
would not provide absolute certainty respecting the 
scope of an amended patent claim. But even strictly 
literal interpretations of claims give rise to questions of 
construction and, hence, even the court of appeals’ 
complete bar cannot provide absolute certainty. The 
position that we urge can substantially diminish the 
unacceptably high level of uncertainty that presently 
inheres in the application of prosecution history 
estoppel but still fairly protect the interests of patent 
holders. Like the application of the doctrine of equiva- 

28 

lents itself, the application of the presumption would 
require courts to exercise judgment and discipline to 
ensure that the patent claims remain the primary 
source for determining the scope of patent protection. 
But that exercise of judgment is unavoidable under a 
system of patent laws that seeks to balance the public’s 
need for clarity of patent coverage against the patent 
holder’s need for fair protection from infringement. 

C. The Court Of Appeals’ Judgment Should Be Vacated 

And The Case Should Be Remanded To The District 

Court For Further Proceedings 

The court of appeals concluded that, because the 
relevant claim elements of the Stoll and Carroll patents 
were the product of amendments that narrowed the 
claims, and because Festo did not establish explana- 
tions for those amendments unrelated to patentability, 
the amendments gave rise to prosecution history 
estoppel, which had the effect of completely barring 
application of the doctrine of equivalents to the 
amended portions of those claims. Pet. App. 56a. If the 
Court concludes that the court of appeals erred in 
categorically imposing a complete bar, that court’s 
judgment should be vacated and the case should be 
remanded for further proceedings to determine what 
role, if any, the doctrine of equivalents should play in 
this infringement action. 

Because the patent law landscape has changed con- 
siderably since the district court initially entered its 
judgment in 1994, and because further assessment of 
the facts may be necessary, the court of appeals should 
remand the case to the district court for reconsideration 
in the first instance. The initial inquiry on remand 
should be whether the relevant claims of the Stoll and 
Carroll patents were narrowed by amendment, in a 

29 

respect relevant to the alleged infringement, for rea- 
sons related to patentability. If so, then prosecution 
history estoppel applies and the district court should 
place the burden on Festo to show, from the patent 
prosecution record and the characteristics of the 
claimed infringement, that the presumption that the 
literal terms of the relevant claim elements describe the 
full scope of the patents is unwarranted. Festo may 
make such a showing, for example, by demonstrating 
that the allegedly equivalent elements are later-devel- 
oped technologies that were not known to persons of 
ordinary skill in the art and were therefore not 
surrendered through the claim amendments. Or Festo 
may make such a showing by demonstrating that 
persons of ordinary skill in the art could not reasonably 
have drafted a patent claim that literally encompassed 
the allegedly equivalent elements. 

30 

CONCLUSION 

The judgment of the court of appeals should be 
vacated and the case should be remanded for further 
proceedings consistent with the foregoing analysis. 

Respectfully submitted. 

JAMES A. TOUPIN 

General Counsel 

JOHN M. WHEALAN 

Solicitor 

LINDA MONCYS ISACSON 
CYNTHIA C. LYNCH 
MARK NAGUMO 

Associate Solicitors 
United States Patent and 

Trademark Office 
THEODORE B. OLSON 
Solicitor General 

STUART E. SCHIFFER 

Acting Assistant Attorney 

General 

LAWRENCE G. WALLACE 

Deputy Solicitor General 

JEFFREY P. MINEAR 

Assistant to the Solicitor 

General 

VITO J. DIPIETRO 
ANTHONY J. STEINMEYER 
JOHN FARGO 
HOWARD S. SCHER 
GRACE KARAFFA 

Attorneys 

AUGUST 2001