FESTO CORPORATION, Plaintiff-Appellee, v. SHOKETSU KINZOKU KOGYO KABUSHIKI CO., LTD., a/k/a SMC Corporation, and SMC Pneumatics, Inc., Defendants-Appellants, 234 F.3d 558

Opinion for the court filed by Circuit Judge SCHALL, in which Chief Judge MAYER and Circuit Judges PLAGER, LOURIE, CLEVENGER, BRYSON, GAJARSA, and DYK join; in which Circuit Judges MICHEL, RADER, and LINN join with respect to PARTS III-A, III-B, and III — D; and in which Circuit Judge MICHEL joins with respect to

PART III-E. Concurring opinion filed by Circuit Judge PLAGER. Concurring opinion filed by Circuit Judge LOURIE. Opinion concurring-in-part and dissenting-in-part with respect to

PART III-C filed by Circuit Judge MICHEL, in which Circuit Judge RADER joins. Opinion concurring-in-part and dissenting-in-part with respect to

PART III-C filed by Circuit Judge RADER, in which Circuit Judges MICHEL and LINN join. Opinion concurring-in-part and dissenting-in-part with respect to

PART III-C filed by Circuit Judge LINN, in which Circuit Judge RADER joins. Opinion concurring-in-part and dissenting-in-part with respect to PARTS III-A, III-B, III-C, and IV filed by Circuit Judge PAULINE NEWMAN. SCHALL, Circuit Judge. This is an appeal from the judgment of the United States District Court for the District of Massachusetts that Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd. (also known as SMC Corporation) and SMC Pneumatics, Inc. (collectively, “SMC”) infringed U.S. Patent No. 4,354,125 (the “Stoll patent”) and U.S. Patent No.

B1 3,779,401 (the “Carroll patent”), both owned by Festo Corporation (“Festo”), under the doctrine of equivalents. We took the case en banc to resolve certain issues relating to the doctrine of equivalents that remained in the wake of the Supreme Court’s decision in Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17, 117 S.Ct. 1040, 137 L.Ed.2d 146 (1997). Specifically, we asked the parties to brief the following five questions for rehearing en banc: 1.

For the purposes of determining whether an amendment to a claim creates prosecution history estoppel, is “a substantial reason related to patentability,” Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 33, 117 S.Ct. 1040, 137 L.Ed.2d 146 (1997), limited to those amendments made to overcome prior art under § 102 and § 103, or does “patentability” mean any reason affecting the issuance of a patent? 2.

Under Wamer-Jenkinson, should a “voluntary” claim amendment — one not required by the examiner or made in response to a rejection by an examiner for a stated reason — create prosecution history estoppel? 3. If a claim amendment creates prosecution history estoppel, under Wamer-Jenkinson what range of equivalents, if any, is available under the doctrine of equivalents for the claim element so amended? 4.

When “no explanation [for a claim amendment] is established,” Warner-Jenkinson, 520 U.S. at 33, 117 S.Ct. 1040, thus invoking the presumption of prosecution history estoppel under Wamer-Jenkinson, what range of equivalents, if any, is available under the doctrine of equivalents for the claim element so amended? 5.Would a judgment of infringement in this case violate Wamer-Jenkinson’s requirement that the application of the doctrine of equivalents “is not allowed such broad play as to eliminate [an] element in its entirety,” 520 U.S. at 29, 117 S.Ct. 1040.

In other words, would such a judgment of infringement, post Wamer-Jenkinson, violate the “all elements” rule? Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 187 F.3d 1381, 1381-82, 51 U.S.P.Q.2d 1959, 1959-60 (Fed.Cir.1999) (“Festo V”). We begin with a brief synopsis of our answers to the en banc questions and a

summary of how those answers affect the disposition of this appeal. In response to En Banc Question 1, we hold that “a substantial reason related to patentability” is not limited to overcoming prior art, but includes other reasons related to the statutory requirements for a patent. Therefore, an amendment that narrows the scope of a claim for any reason related to the statutory requirements for a patent will give rise to prosecution history estop-pel with respect to the amended claim element.

In response to En Banc Question 2, we hold that “voluntary” claim amendments are treated the same as other claim amendments; therefore, any voluntary amendment that narrows the scope of a claim for a reason related to the statutory requirements for a patent will give rise to prosecution history estoppel with respect to the amended claim element. In response to En Banc Question 3, we hold that when a claim amendment creates prosecution history estoppel, no range of equivalents is available for the amended claim element.

In response to En Banc Question 4, we hold that “unexplained” amendments are not entitled to any range of equivalents. We do not reach En Banc Question 5, for reasons which will become clear in our discussion of the specific case before us. In view of our answers to the en banc questions, we reverse the judgment that claim 1 of the Stoll patent and claims 5, 6, and 9 of the Carroll patent were infringed under the doctrine of equivalents. The claim elements that were found to be infringed by equivalents were added during prosecution of the Stoll patent and during reexamination of the Carroll patent.

The amendments that added those elements narrowed the scope of the claims. Festo has not established explanations unrelated to patentability for these amendments; accordingly, no range of equivalents is available for the amended claim elements. Because the parties agree that SMC does not produce a device that literally satisfies those claim elements, the judgment of infringement must be reversed.

Section I of this opinion provides a brief overview of the doctrine of equivalents and prosecution history estoppel.

Section II discusses the Supreme Court’s decision in Wamer-Jenkinson.

Section III sets forth our answers to the en banc questions. In

Section IV, we decide the appeal before us by applying our answers to the en banc questions to the facts of the case. DISCUSSION I. The Doctrine of Equivalents and Prosecution History Estoppel The doctrine of equivalents prevents an accused infringer from avoiding liability for infringement by changing only minor or insubstantial details of a claimed invention while retaining the invention’s essential identity. Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 389 U.S. 605, 608, 70 S.Ct. 854, 94 L.Ed. 1097 (1950).

The doctrine of equivalents is utilized “ ‘[t]o temper unsparing logic and prevent an infringer from stealing the benefit of the invention.’ ” Id. (quoting Royal Typewriter Co. v. Remington Rand, Inc., 168 F.2d 691, 692, 77 U.S.P.Q. 517, 518 (2d Cir.1948) (Hand, J.)). In pursuing these goals, the doctrine attempts to strike a balance between ensuring that the paten-tee enjoys the full benefit of his patent and ensuring that the claims give “fair notice” of the patent’s scope. London v. Carson Pirie Scott & Co., 946 F.2d 1534, 1538, 20 U.S.P.Q.2d 1456, 1458-59 (Fed.Cir.1991).

This balance can be easily upset, however, because “the doctrine of equivalents, when applied broadly, conflicts with the definitional and public-notice functions of the statutory claiming requirement.” Warner-Jenkinson, 520 U.S. at 29, 117 S.Ct. 1040. Prosecution history estoppel is one tool that prevents the doctrine of equivalents from vitiating the notice function of claims. Charles Greiner & Co. v. Mari-Med Mfg., Inc., 962 F.2d 1031, 1036, 22 U.S.P.Q.2d 1526, 1529-30 (Fed.Cir.1992).

Actions by the patentee, including claim amendments and arguments made before the Patent Office, may give rise to prosecution history estoppel. Pharmacia & Upjohn Co. v. Mylan Pharms., Inc., 170 F.3d 1373, 1376-77, 50 U.S.P.Q.2d 1033, 1036 (Fed.Cir.1999). “Prosecution history estoppel precludes a patentee from obtaining under the doctrine of equivalents coverage of subject matter that has been relinquished during the prosecution of its patent application.” Id. at 1376, 170 F.3d 1373, 50 U.S.P.Q.2d at 1036.

Therefore, “[t]he doctrine of equivalents is subservient to ... [prosecution history] estoppel.” Autogiro Co. v. United States, 181 Ct.Cl. 55, 384 F.2d 391, 400-01, 155 U.S.P.Q. 697, 705 (1967). The logic of prosecution history estoppel is that the patentee, during prosecution, has created a record that fairly notifies the public that the patentee has surrendered the right to claim particular matter as within the reach of the patent. II.

Wamer-Jenkinson In this en banc rehearing, we focus our attention on the effect of Wamer-Jenkin-son on our case law relating to the doctrine of equivalents and prosecution history estoppel. Festo V, 187 F.3d at 1381-82, 51 U.S.P.Q.2d at 1959-60; see also Shoketsu Kinzoku Kogyo Kabushiki Co. v. Festo Corp., 520 U.S. 1111, 117 S.Ct. 1240, 137 L.Ed.2d 323 (1997) (“Festo III ”) (remanding the case for further consideration in light of the Wamer-Jenkinson decision).

The patent before the Court in Wamer-Jenkinson disclosed an improved process for purifying dyes which used a method called “ultrafiltration.” Wamer-Jenkin-son, 520 U.S. at 21, 117 S.Ct. 1040. During prosecution, the patentee amended the claims to recite that the process is carried out “at a pH from approximately 6.0 to 9.0.” Id. at 22, 117 S.Ct. 1040. The accused process was carried out at a pH of 5.0. Id. at 23, 117 S.Ct. 1040. In light of these facts, the Supreme Court embarked on an “endeavor to clarify the proper scope of the doctrine” of equivalents. Id. at 21, 117 S.Ct. 1040.

The Court dismissed the arguments of Warner-Jenkinson (the alleged infringer) that the doctrine of equivalents, as established in Graver Tank, did not survive the 1952 revision of the Patent Act. Id. at 25-27, 117 S.Ct. 1040. The Court nevertheless noted its concern that “the doctrine of equivalents, as it has come to be applied since Graver Tank, has taken on a life of its own.” Id. at 28-29, 117 S.Ct. 1040. The Court agreed with Warner-Jenkinson “that Graver Tank did not dispose of prosecution history estoppel as a legal limitation on the doctrine of equivalents.” Id. at 30, 117 S.Ct. 1040.

However, the Court rejected Warner-Jenkinson’s argument “that the reason for an amendment during patent prosecution is irrelevant to any subsequent estoppel.” Id. The Court noted that “[i]n each of our cases cited by petitioner and by the dissent below, prosecution history estoppel was tied to amendments made 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.” Id. at 30-31, 117 S.Ct. 1040.

The Court therefore saw “no substantial cause for requiring a more rigid rule invoking an estoppel regardless of the reasons for a change.” Id. at 32, 117 S.Ct. 1040 (footnote omitted). Turning to the facts at hand, the Court noted that, although the parties did not dispute that the upper pH limit of 9.0 was added to avoid the prior art, “the reason for adding the lower limit of 6.0 is unclear.” Id.

Presented “with the problem ... where the record seems not to reveal the reason for including the lower pH limit of 6.0,” the Court “place[d] the burden on the patent holder to establish the reason for an amendment required during patent prosecution.” Id. at 33, 117 S.Ct. 1040. The Court stated that courts will have to “decide whether the [proffered] reason is sufficient to overcome prosecution history estoppel as a bar to application of the doctrine of equivalents to the element added by that amendment.” Id.

The Court also stated that “[wjhere no explanation is established, ... the court should presume that the patent applicant had a substantial reason related to patentability for including the limiting element added by the amendment.” Id. Therefore, “prosecution history estoppel would bar the application of the doctrine of equivalents as to that element.” Id.

Because Hilton Davis had “not proffered in ... [the Supreme] Court a reason for the addition of the lower pH limit,” the Court remanded the case for this court to consider whether Hilton Davis had offered reasons for the amendment that added the lower pH limit and to determine whether Hilton Davis should be given the opportunity to establish such reasons. Id. at 34, 117 S.Ct. 1040. The Court rejected the other restrictions on the doctrine of equivalents proposed by Warner-Jenkinson. Id. at 35-40, 117 S.Ct. 1040.

Specifically, the Court refused to “require judicial exploration of the equities of a case before allowing application of the doctrine of equivalents,” id. at 34, 117 S.Ct. 1040, refused to require “proof of intent” on the part of the alleged infringer before the doctrine of equivalents could be applied, id. at 35-36, 117 S.Ct. 1040, and refused to adopt “independent experimentation” as “an equitable defense to the doctrine of equivalents,” id. at 36, 117 S.Ct. 1040.

The Court also refused to limit the doctrine of equivalents “to equivalents that are disclosed within the patent itself,” reasoning that the “proper time for evaluating equivalency ... is at the time of infringement, not at the time the patent was issued.” Id. at 37, 117 S.Ct. 1040. In closing, the Court stated that it chose to “adhere to the doctrine of equivalents,” which “should be applied as an objective inquiry on an element-by-element basis.” Id. at 40, 117 S.Ct. 1040. The Court noted that “[pjrosecution history estoppel continues to be available as a defense to infringement.” Id.

However, “if the patent holder demonstrates that an amendment required during prosecution had a purpose unrelated to patentability, a court must consider that purpose in order to decide whether an estoppel is precluded.” Id. at 40-41, 117 S.Ct. 1040. If “the patent holder is unable to establish such a purpose, a court should presume that the purpose behind the required amendment is such that prosecution history estoppel would apply.” Id. at 41, 117 S.Ct. 1040. III. Answers to the En Banc Questions A.

Question 1 For the purposes of determining whether an amendment to a claim creates prosecution history estoppel, is “a substantial reason related to patentability,” Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 33, 117 S.Ct. 1040, 137 L.Edüd 146 (1997), limited to those amendments made to overcome prior art under § 102 and § 103, or does “patentability” mean any reason affecting the issuance of a patent?

We answer Question 1 as follows: For the purposes of determining whether an amendment gives rise to prosecution history estoppel, a “substantial reason related to patentability” is not limited to overcoming or avoiding prior art, but instead includes any reason which relates to the statutory requirements for a patent. Therefore, a narrowing 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.

It is true that in Wamer-Jenkinson the Supreme Court focused on claim amendments made to overcome or avoid prior art. Warner-Jenkinson, 520 U.S. at 30-34, 117 S.Ct. 1040. However, there are a number of statutory requirements that must be satisfied before a valid patent can issue and that thus relate to patentability. In addition to satisfying the novelty and non-obviousness requirements of 35 U.S.C. §§ 102 and 103, 35 U.S.C.A. §§ 102, 103 (West 1994 & Supp.2000), the claims must be directed to patentable subject matter and the claimed invention must be useful, as set forth in 35 U.S.C. § 101 (1994).

Additionally, the first paragraph of 35 U.S.C. § 112 requires that the patent specification describe, enable, and set forth the best mode of carrying out the invention, 35 U.S.C. § 112, ¶ 1 (1994), while the second paragraph of

section 112 requires that the claims set forth the subject matter that the applicant regards as his invention and that the claims particularly point out and distinctly define the invention, 35 U.S.C. § 112, ¶ 2 (1994). The Patent Ofi fice will reject a patent application that fails to satisfy any one of these statutory requirements. See Man. Pat. Exam. P. 2100-1 to -173 (7th ed. rev. 1 1998). And any one of these requirements may be a ground for invalidating an issued patent. E.g., 35 U.S.C. § 282 (1994); Atlas Powder Co. v.

Ireco, Inc., 190 F.3d 1342, 51 U.S.P.Q.2d 1943 (Fed.Cir.1999) (holding a patent invalid because the claims were anticipated under 35 U.S.C. § 102); Mitsubishi Elec. Corp. v. Ampex Corp., 190 F.3d 1300, 51 U.S.P.Q.2d 1910 (Fed.Cir.1999) (holding a patent invalid because the claims were obvious under 35 U.S.C. § 103); State Street Bank & Trust Co. v. Signature Fin. Group, Inc., 149 F.3d 1368, 47 U.S.P.Q.2d 1596 (Fed.Cir.1998) (discussing the patentable subject matter requirement of 35 U.S.C. § 101); Process Control Corp. v.

HydReclaim Corp., 190 F.3d 1350, 52 U.S.P.Q.2d 1029 (Fed.Cir.1999) (holding a patent invalid because the claims were inoperative and therefore failed to satisfy the utility requirement of 35 U.S.C. § 101); Johnson Worldwide Assoc., Inc. v. Zebco Corp., 175 F.3d 985, 50 U.S.P.Q.2d 1607 (Fed.Cir.1999) (considering whether a patent claim was invalid under the written description requirement of § 112, ¶ 1); Gentry Gallery, Inc. v.

Berkline Corp., 134 F.3d 1473, 45 U.S.P.Q.2d 1498 (Fed.Cir.1998) (holding claims of a patent invalid for failing to comply with the written description requirement of § 112, ¶ 1); Enzo Biochem, Inc. v. Calgene, Inc., 188 F.3d 1362, 52 U.S.P.Q.2d 1129 (Fed.Cir.1999) (holding a patent invalid because the claims were not enabled, as required by 35 U.S.C. § 112, ¶ 1); United States Gypsum Co. v. Nat’l Gypsum Co., 74 F.3d 1209, 37 U.S.P.Q.2d 1388 (Fed.Cir.1996) (holding a patent invalid for failing to satisfy the best mode requirement of 35 U.S.C. § 112, ¶ 1); Morton Int’l, Inc. v. Cardinal Chem.

Co., 5 F.3d 1464, 28 U.S.P.Q.2d 1190 (Fed.Cir.1993) (holding a patent invalid because the claims failed to satisfy the definiteness requirement of 35 U.S.C. § 112, ¶ 2). An amendment related to any of these statutory requirements is an amendment made for “a substantial reason related to patent-ability.” The law has been clear that amendments made to avoid prior art give rise to prosecution history estoppel. E.g., Warner-Jenkinson, 520 U.S. at 30-31, 117 S.Ct. 1040 (discussing Exhibit Supply Co. v. Ace Patents Corp., 315 U.S. 126, 62 S.Ct. 513, 86 L.Ed. 736 (1942), and Keystone Driller Co. v.

Northwest Eng’g Corp., 294 U.S. 42, 55 S.Ct. 262, 79 L.Ed. 747 (1935)). In view of the functions of prosecution history estoppel — preserving the notice function of the claims and preventing patent holders from recapturing under the doctrine of equivalents subject matter that was surrendered before the Patent Office — we see no reason why prosecution history estoppel should not also arise from amendments made for other reasons related to patentability, as described above.

Indeed, the functions of prosecution history estoppel cannot be fully satisfied if substantial reasons related to patentability are limited to a narrow subset of patentability issues. Rather, substantial reasons related to patentability include 35 U.S.C. §§ 101 and 112 issues, as well as 35 U.S.C. §§ 102 and 103 issues. While we do not believe that the Supreme Court itself answered this question in Wamer-Jenkinson, we do believe that our answer is not inconsistent with Wamer-Jenkinson.

Warner-Jenkinson describes prior cases as applying prosecution history estoppel “typically because what [was previously claimed] ... was encompassed within the prior art,” 520 U.S. at 31, 117 S.Ct. 1040 (emphasis added), but no language in Wamer-Jenkinson limits prosecution history estoppel to amendments made to avoid prior art. See also Crawford v. Heysinger, 123 U.S. 589, 606, 8 S.Ct. 399, 31 L.Ed. 269 (1887) (finding prosecution history estoppel to arise from amendments made in response to operability rejections).

Moreover, our approach is consistent with Wamer-Jenkinson’s requirement that an amendment “does not necessarily preclude infringement by equivalents of that element.” Id. at 33, 117 S.Ct. 1040. Thus, if a patent holder can show from the prosecution history that a claim amendment was not motivated by patentability concerns, the amendment will not give rise to prosecution history estop-pel. B. Question 2 Under Wamer-Jenkinson, should a “voluntary” claim amendment — one not required by the examiner or made in response to a rejection by an examiner for a stated reason — create prosecution history estoppel?

We answer Question 2 as follows: Voluntary claim amendments are treated the same as other amendments. Therefore, a voluntary amendment that narrows the scope of a claim for a reason related to the statutory requirements for a patent will give rise to prosecution history estoppel as to the amended claim element. Both voluntary amendments and amendments required by the Patent Office signal to the public that subject matter has been surrendered.

There is no reason why prosecution history estoppel should arise if the Patent Office rejects a claim because it believes the claim to be unpatentable, but not arise if the applicant amends a claim because he believes the claim to be unpat-entable. Our answer to this question is consistent with the doctrine of argument-based estoppel. Arguments made voluntarily during prosecution may give rise to prosecution history estoppel if they evidence a surrender of subject matter. Eg., KCJ Corp. v.

Kinetic Concepts, Inc., 223 F.3d 1351, 1359-60, 55 U.S.P.Q.2d 1835, 1841-42 (Fed.Cir.2000) (concluding that “KCJ’s statements [during prosecution] reflect a clear and unmistakable surrender” of subject matter that cannot be reclaimed through the doctrine of equivalents); Bayer AG v. Elan Pharm.

Research Corp., 212 F.3d 1241, 1252-53, 54 U.S.P.Q.2d 1711, 1719 (Fed.Cir.2000) (finding that “through [Bayer’s] statements to the PTO and the declarations it filed, Bayer made statements of clear and unmistakable surrender of subject matter” which it could not recapture through the doctrine of equivalents); Pharmacia & Upjohn, 170 F.3d at 1377, 50 U.S.P.Q.2d at 1036 (“A number of activities during prosecution may give rise to prosecution history estoppel, ... including arguments made to obtain allowance of the claims at issue.” (citation omitted)); Southwall Techs., Inc. v.

Cardinal IG Co., 54 F.3d 1570, 1583, 34 U.S.P.Q.2d 1673, 1682 (Fed.Cir.1995) (“Clear assertions made during prosecution in support of pat-entability, whether or not actually required to secure allowance of the claim, may ... create an estoppel.”); Texas Instruments Inc. v. United States Int’l Trade Comm’n, 988 F.2d 1165, 1174, 26 U.S.P.Q.2d 1018, 1025 (Fed.Cir.1993) (holding that arguments made during prosecution that emphasized one feature of the invention es-topped the patent holder from asserting that a device lacking that feature infringed the patent under the doctrine of equivalents).

There is no reason why an amendment-based surrender of subject matter should be given less force than an argument-based surrender of subject matter. We also believe that our answer to this question is consistent with Wamer-Jen-kinson. Although the Supreme Court spoke of “required” amendments, the claim amendment at issue in Wamer-Jenkinson, the addition of the lower pH limit of 6, was not “required” by the prior art rejection. The original claim recited an ultrafiltration process. Wamer-Jenkinson, 520 U.S. at 21, 117 S.Ct. 1040.

The asserted prior art reference taught an ultrafiltration process conducted at a pH of above 9. Id. at 22, 117 S.Ct. 1040. The amended claim recited an ultrafiltration process conducted “at a pH from approximately 6.0 to 9.0.” Id. The parties did not dispute that the upper pH limit of 9.0 was added to distinguish the prior art. Id. at 32, 117 S.Ct. 1040. The Court, however, was unable to discern the reason for the addition of the lower pH limit of 6. Id. at 32-33, 117 S.Ct. 1040. Accordingly, the amendment at issue in Wamer-Jenkinson appears to have been voluntary with respect to the lower pH limit.

Nevertheless, the Court held that the amendment adding the lower pH limit could give rise to prosecution history es-toppel. Id. at 34, 117 S.Ct. 1040. C. Question 3 If a claim amendment creates prosecution history estoppel, under Wamer-Jenkinson what range of equivalents, if any, is available under the doctrine of equivalents for the claim element so amended? We answer Question 3 as follows: When 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.

Application of the doctrine of equivalents to the claim element is completely barred (a “complete bar”). We think it is fair to say that the question of the scope of equivalents available when prosecution history estoppel applies to a claim element has not been directly addressed or answered by the Supreme Court, at least in circumstances where the claim was amended for a known patenta-bility reason.

In Wamer-Jenkinson, the Court focused its attention more on the circumstances under which prosecution history estoppel arises than on the range of equivalents that might generally be available despite the existence of prosecution history estoppel. Warner-Jenkinson, 520 U.S. at 30-34, 117 S.Ct. 1040. The Court did not discuss the upper pH limit of 9.0, other than to note that the upper limit, which narrowed the claim, was selected to overcome prior art. Id. at 32, 117 S.Ct. 1040. The range of equivalents, if any, that could be asserted for the upper pH limit was not discussed by the Court.

The only statements in Wamer-Jenkinson as to the range of equivalents that is available when prosecution history estoppel applies are found in the Court’s discussion of unexplained amendments. Id. at 33-34, 117 S.Ct. 1040. For those amendments, the Court held that “prosecution history estoppel would bar the application of the doctrine [of] equivalents as to that element.” Id. at 33, 117 S.Ct. 1040. 1.

In cases before Wamer-Jenkinson, the Supreme Court applied prosecution history estoppel to preclude a finding of infringement under the doctrine of equivalents, but the Court did not analyze the actual scope of equivalents that might be available when prosecution history estop-pel applied, i.e., the extent of the subject matter surrendered by amendment. In Weber Electric Co. v. E.H.

Freeman Electric Co., 256 U.S. 668, 41 S.Ct. 600, 65 L.Ed. 1162 (1921), the patentee had amended his claim to an electric lamp socket to overcome prior art that taught a socket and electric bulb that were unlocked and locked together simply by rotation. The amended claim recited, instead, a bulb and socket combination that unlocked and locked by manual compression. Id. at 677, 41 S.Ct. 600.

In light of this amendment, the Court did not allow the patentee, who had “narrowed his claim ... to obtain a patent,” to “resort to the doctrine of equivalents [and] give to the claim the larger scope which it might have had without the amendment.” Id. Under the facts of the case, the alleged infringer practiced the exact subject matter described in the prior art, a combination that locked the bulb by rotational movement. Id. at 678, 41 S.Ct. 600. Thus, the Court did not need to discuss the precise contours of the subject matter surrendered by the claim amendment. A similar situation was presented in Smith v.

Magic City Kennel Club, 282 U.S. 784, 51 S.Ct. 291, 75 L.Ed. 707 (1931). The invention at issue in that case involved an artificial dog race track lure. Id. at 786-87, 51 S.Ct. 291. The patentee overcame prior art that disclosed a straight arm for holding the lure by amending his claims to recite a hinged arm. Id. at 788-89, 51 S.Ct. 291. The accused infringer’s device used a rigid arm. Id. The Court did not allow the patentee to resort to the doctrine of equivalents to regain the specific subject matter the patentee had surrendered “in order to escape rejection.” Id. at 790, 51 S.Ct. 291.

In Magic City Kennel Club, as in Weber, the accused ■ device read on the prior art, which in and of itself mandates a finding of noninfringement, see Wilson Sporting Goods Co. v. David Geoffrey & Assocs., 904 F.2d 677, 683-85, 14 U.S.P.Q.2d 1942, 1947-49 (Fed.Cir.1990) (noting that the doctrine of equivalents cannot be applied to encompass the prior art). In Exhibit Supply Co. v. Ace Patents Corp., 315 U.S. 126, 62 S.Ct. 513, 86 L.Ed. 736 (1942), the patentee amended the claim at issue to overcome general prior art cited by the examiner.

He did so by changing the claim to recite a conductor device that was “embedded in” a game table (pinball machine) instead of one that was “carried by” the table. Exhibit Supply, 315 U.S. at 136-37, 62 S.Ct. 513. The Court held that the patentee could not thereafter, through the doctrine of equivalents, obtain coverage of accused devices in which the “conductor means” was carried by the game table instead of imbedded in it. Id. It is unclear from the Court’s opinion whether the accused device was in the prior art cited by the examiner in his rejection.

Id. at 133, 62 S.Ct. 513 (quoting the examiner’s assertion that it was plainly “old in the art to make an electrical contact by flexing a coil spring as shown by the art already cited in the case”).

The Court stated, however: Had Claim 7 been allowed in its original form, it would have read upon all the accused devices, since in all the conductor means complementary to the coil spring are “carried by the table.” By striking that phrase from the claim and substituting for it “embedded in the table,” the applicant restricted his claim to those combinations in which the conductor means, though carried on the table, is also embedded in it. By the amendment, he recognized and emphasized the difference between the two phrases and proclaimed his abandonment of all that is embraced in that difference.

Id. at 136, 62 S.Ct. 513. The Court never addressed the exact range of equivalents that might still be available under the amended claim, and the “difference between” the original claim and the amended claim, the difference said by the Court to have been abandoned by the patentee, was never explicitly defined. In his dissenting opinion, Judge Michel relies upon Goodyear Dental Vulcanite Co. v. Davis, 102 U.S. 222, 26 L.Ed. 149 (1880), and Hurlbut v.

Schillinger, 130 U.S. 456, 9 S.Ct. 584, 32 L.Ed. 1011 (1889), for the proposition that a patentee is entitled to a range of equivalents despite the fact that the scope of a claim has been limited by amendment. We do not believe, however, that either of these cases addresses the issue presented in En Banc Question 3: the range of equivalents, if any, that is available under the doctrine of equivalents for a claim element that has been amended by an amendment that creates prosecution history estoppel. As issued, the claim in Goodyear described “rubber or some other elastic material” for a dental plate.

Goodyear, 102 U.S. at 224-25. During reissue the claim was amended to describe a dental plate of hard or “vulcanized” rubber. Id. at 228. Looking to the reissue amendment, the Court concluded that the patentee “regarded the patent to be for a manufacture made exclusively of vulcanites by the detailed process.” Id. The Court determined that there could be no infringement where the defendant’s product used celluloid. Id. at 229-30.

The Court did not discuss prosecution history estoppel, but simply decided that under the language of the reissued patent celluloid was not equivalent to “hard rubber or vulcanite or its equivalent.” Hurlbut involved a patent which had been reissued and in which a disclaimer had been filed. Hurlbut, 130 U.S. at 462-63, 9 S.Ct. 584. The reissue added a second claim, but did not amend any claim language. Id. Claim 1 recited “[a] concrete pavement laid in detached blocks or sections, substantially in the manner shown and described.” Id. at 463, 9 S.Ct. 584.

Claim 2 recited an “arrangement of tar paper, or its equivalent, between adjoining blocks of concrete, substantially as and for the purpose set forth.” Id. The patentee disclaimed “the forming of blocks from plastic material without interposing anything between their joints while in the process of formation.” Id. In the face of this disclaimer, the Court construed the claims to require that the division of the concrete paving blocks be “effected by either a permanent or temporary imposition of something between the blocks.” Id. at 465, 9 S.Ct. 584.

The Court held that both claims were infringed by a process in which a trowel was used to cut a concrete layer into blocks. Id. at 469, 9 S.Ct. 584. In referring to equivalents the Court was referring to the language of the claims (“substantially” in claim 1 and “or its equivalents” in claim 2). Thus, the Court did not discuss the issue of the scope of equivalents that remained under the doctrine of equivalents after the disclaimer.

Neither do we believe that in any of the other cases noted by Judge Michel did the Court determine that a claim element that was amended by an amendment that gave rise to prosecution history estoppel was entitled to a range of equivalents. See Cal. Artificial Stone-Pav Co. v. Schalicke, 119 U.S. 401, 407, 7 S.Ct. 391, 30 L.Ed. 471 (1886) (stating that there was no infringement “under any construction which it is possible to give the claims”); Fay v.

Cordesman, 109 U.S. 408, 420-21, 3 S.Ct. 236, 27 L.Ed. 979 (1883) (finding that the accused device lacked material elements of the claimed inventions without discussing prosecution history estoppel or the doctrine of equivalents); Shepard v. Carrigan, 116 U.S. 593, 597-98, 6 S.Ct. 493, 29 L.Ed. 723 (1886) (reversing a judgment of infringement and noting that the prior art and the accused device depicted a skirt protector without a “fluted or plaited band or border,” while the patent described a skirt protector with such a border); Sutter v.

Robinson, 119 U.S. 530, 541-42, 7 S.Ct. 376, 30 L.Ed. 492 (1886) (reversing a judgment of infringement and stating that the prior art and the accused device involved a metal box for storing tobacco leaves, while the patent described a wooden box); Phoenix Caster Co. v. Spiegel, 133 U.S. 360, 364, 368-69, 10 S.Ct. 409, 33 L.Ed. 663 (1890) (holding that there was no infringement because the accused device did not have, as the claim . recited, a “rocker-formed collar-bearing, or its mechanical equivalent”); Royer v.

Coupe, 146 U.S. 524, 531-32, 13 S.Ct. 166, 36 L.Ed. 1073 (1892) (determining that the defendants could not infringe “under the proper construction of the claim of the patent” because the process they practiced lacked an element of the claimed process); Hubbell v. United States, 179 U.S. 77, 80, 85, 21 S.Ct. 24, 45 L.Ed. 95 (1900) (using prosecution history to construe the claim and finding no infringement, without discussing prosecution history estoppel).

In short, the range of equivalents available to an amended claim element simply was not before the Supreme Court in the cases Judge Michel cites, and the Supreme Court did not discuss the issue presented in En Banc Question 3. Although a court must follow “explicit and carefully considered” language of the Supreme Court, see Stone Container Corp. v. United States, 229 F.3d 1345, 1350 (Fed.Cir.2000), none of the language cited by Judge Michel constitutes explicit and carefully considered language regarding the range of equivalents available when a claim amendment gives rise to prosecution history estoppel. 2.

Because the Supreme Court has not fully addressed the range of equivalents that is available once prosecution history estoppel applies, we must independently decide the issue. Congress specifically created the Federal Circuit to resolve issues unique to patent law, Markman v. Westview Instruments, Inc., 517 U.S. 370, 390, 116 S.Ct. 1384, 134 L.Ed.2d 577 (1996) (citing H.R.Rep. No. 97-312, pp. 20-23 (1981)), such as those regarding prosecution history estoppel, which is a judicially created doctrine, Hormone Research Found., Inc. v. Genentech, Inc., 904 F.2d 1558, 1564, 15 U.S.P.Q.2d 1039, 1044 (Fed.Cir.1990).

Congress contemplated that the Federal Circuit would “strengthen the United States patent system in such a way as to foster technological growth and industrial innovation.” Markman, 517 U.S. at 390, 116 S.Ct. 1384. Issues such as the one before us in this case are properly reserved for this court to answer with “its special expertise.” Warner-Jenkinson, 520 U.S. at 40, 117 S.Ct. 1040 (reserving explicitly for the Federal Circuit the task of formulating the proper test(

s) for infringement under the doctrine of equivalents). The Federal Circuit first addressed the range of equivalents that is available when prosecution history applies in Hughes Aircraft Co. v. United States, 717 F.2d 1351, 219 U.S.P.Q. 473 (Fed.Cir.1983) (“Hughes I”). In that case, we recognized that, prior to creation of the Federal Circuit, some regional circuits had followed a flexible bar approach to prosecution history estoppel, whereas others had applied a strict rule of complete surrender when prosecution history estoppel applied. Id. at 1362-63, 717 F.2d 1351, 219 U.S.P.Q. at 481-82.

We decided to apply prosecution history estoppel as a flexible bar, stating that prosecution history estoppel “may have a limiting effect” on the doctrine of equivalents “within a spectrum ranging from great to small to zero.” Id. at 1363, 717 F.2d 1351, 219 U.S.P.Q. at 481-82. LaBounty Manufacturing, Inc. v. United States International Trade Commission, 867 F.2d 1572, 9 U.S.P.Q.2d 1995 (Fed.Cir.1989), is an example of the flexible bar approach.

In LaBounty, we vacated the noninfringement determination of the International Trade Commission (“ITC”) and remanded the case to the ITC for further proceedings because the administrative law judge (“ALJ”) had failed to determine the scope of prosecution history estoppel and had held, instead, that once an element of a claim is amended, no equivalent of that element can be asserted. LaBounty, 867 F.2d at 1576, 9 U.S.P.Q.2d at 1999. In Black & Decker, Inc. v.

Hoover Service Center, 886 F.2d 1285, 1295, 12 U.S.P.Q.2d 1250, 1258-59 (Fed.Cir.1989), we held that an amendment made during prosecution did not prevent a finding of infringement under the doctrine of equivalents. We reasoned that although the amendment would bar infringement under the doctrine of equivalents with respect to a device similar to the prior art that had provoked the amendment, prosecution history estoppel did not prevent all applications of the doctrine of equivalents. Id.; see also Dixie USA, Inc. v.

Infab Corp.; 927 F.2d 584, 588, 17 U.S.P.Q.2d 1968, 1970-71 (Fed.Cir.1991) (noting that prosecution history estoppel should not cause “a total preclusion of equivalence”). Similarly, in Modine Manufacturing Co. v.

United States International Trade Commission, 75 F.3d 1545, 1555-56, 37 U.S.P.Q.2d 1609, 1616 (Fed.Cir.1996), we vacated the ALJ’s holding of lack of infringement under the doctrine of equivalents due to prosecution history estoppel because, although “the available range of equivalency is limited, by estoppel, ... the prosecution history and the prior art do not eliminate equivalents.” Less than a year after Hughes I, however, a five-judge panel of this court decided Kinzenbaw v. Deere & Co., 741 F.2d 383, 222 U.S.P.Q. 929 (Fed.Cir.1984).

The claimed invention in Kinzenbaw was “[a]n apparatus for forming seed planting furrows.” Id. at 388, 741 F.2d 383, 222 U.S.P.Q. at 932. The claim element at issue related to “a pair of depth gauge compacting wheels” that controlled the depth of the furrow created by the planter. Id. During prosecution, in order to overcome an examiner’s rejection and to obtain his patent, the inventor narrowed his claims by specifying, among other things, that the gauge wheels had to have a radius less than that of the radius of the blades of the planter (called “discs”). Id.

On the accused device, the gauge wheels had a radius greater than that of the discs. Id. at 388-89, 741 F.2d 383, 222 U.S.P.Q. at 932. Consequently, the accused device could not literally infringe. As a result, the patentee (Deere) sought to prove infringement under the doctrine of equivalents. Id. at 389, 741 F.2d 383, 222 U.S.P.Q. at 932. The district court concluded that prosecution history estoppel precluded Deere from relying upon the doctrine of equivalents. Id., 222 U.S.P.Q. at 933.

The court determined that, as far as the gauge wheels were concerned, the inventor had intentionally narrowed his claims, and it refused to permit Deere to avoid, through the doctrine of equivalents, the limitation that the inventor had placed on his claims. Id. On appeal, Deere urged that prosecution history estoppel did not apply because the inventor’s limitation of his claims to devices in which the gauge wheels had a smaller radius than that of the discs was unnecessary to distinguish the prior art. Id.

Specifically, Deere contended that only that portion of the claim that provided that the radius of the gauge wheels had to exceed the distance from the axes of the wheels to the rear edges of the discs was necessary in order to render the claims patentable over the prior art. Id. The five-judge panel rejected Deere’s argument. It stated: “We decline to undertake the speculative inquiry whether, if ... [the inventor] had made only that narrowing limitation in his claim, the examiner nevertheless would have allowed it.” Id. The court therefore affirmed the district court’s judgment of noninfringement.

Id. at 391, 222 U.S.P.Q. at 934. The approach to prosecution history es-toppel that was followed in Kinzenbaw prompted the following observation by Professor Chisum: “Beginning shortly after its creation in 1982, the Federal Circuit developed two lines of authority on the scope of an estoppel based on an amendment or argument that distinguished the prior art. One line followed a strict approach, according to which a court refused to speculate whether a narrower amendment would have been allowed.

The other line followed a flexible or spectrum approach, which recognized that amendments did not invariably preclude all equivalence .... ” 5A Donald S. Chisum, Chisum on Patents § 18.05[3][b], at 18-492 (1998). Soon after Hughes I and Kinzenbaw were decided they were the subject of comment in the American University Law Review, which annually reviews the work of the Federal Circuit.

The commentators stated that the Federal Circuit’s “two divergent lines of authority dealing with prosecution history estoppel,” the Hughes I line and the Kinzenbaw line, had given rise to ever-increasing “uncertainty and confusion” in patent litigation. Douglas A. Strawbridge et al., Area

Summary, Patent Law Developments in the United States Court of Appeals for the Federal Circuit During 1986, 36 Am. U.L.Rev. 861, 887-88 (1987). The commentary that began after Hughes I and Kinzenbaw were decided has continued. See, e.g., Gregory J. Smith, The Federal Circuit’s Modem Doctrine of Equivalents in Patent Infringement, 29 Santa Clara L. Rev. 901, 921 (1989) (noting that there is at least an “apparent conflict” between Hughes I and Kinzenbaw); Note, To Bar or Not to Bar: Prosecution History Estoppel After Wamer-Jenkinson, 111 Harv. L.

Rev. 2330, 2336 (1998) (stating that the Hughes I line of cases “appear[s] to be irreconcilable” with the Kinzenbaw line of cases). Since Wamer-Jenkinson, panels of this court have continued to visit the question of the range of equivalents that is available after prosecution history estoppel has been determined to exist. Two cases in particular were remanded by the Supreme Court for further consideration in light of Warner-Jenkinson. Honeywell, Inc. v. Litton Sys., Inc., 520 U.S. 1111, 117 S.Ct. 1240, 137 L.Ed.2d 323 (1997); United States v.

Hughes Aircraft Co., 520 U.S. 1211, 117 S.Ct. 1693, 137 L.Ed.2d 820 (1997). In Litton Systems, Inc. v. Honeywell, Inc., 140 F.3d 1449, 1455-57, 46 U.S.P.Q.2d 1321, 1325 (Fed.Cir.1998), this court determined that Wamer-Jenkinson had not changed the “longstanding doctrine that an estoppel only bars recapture of that subject matter actually surrendered during prosecution.” The court noted that “the Supreme Court did not reach the question of the proper scope of estoppel for an amended limitation,” and thus concluded that Wamer-Jenkinson did not affect our already established jurisprudence on the issue.

Id. at 1457, 46 U.S.P.Q.2d at 1327. A similar analysis and conclusion were set forth in Hughes Aircraft Co. v. United States, 140 F.3d 1470, 1476-77, 46 U.S.P.Q.2d 1285, 1289-90 (Fed.Cir.1998) (“Hughes II"). The alleged infringer in that case argued that Warner-Jenkinson mandated that prosecution history estop-pel act as a complete bar and preclude any finding of infringement under the doctrine of equivalents. Hughes II, 140 F.3d at 1476, 46 U.S.P.Q.2d at 1289.

In rejecting this argument, this court stated that there must be a determination as to the exact “subject matter the patentee actually surrendered.” Id. at 1476-77, 46 U.S.P.Q.2d at 1290. Because the accused device did not “fall within the range of subject matter surrendered,” infringement under the doctrine of equivalents was not barred. Id. The court denied rehearing en banc in both Litton and Hughes II, over dissents from the denials. Litton Sys., Inc. v. Honeywell, Inc., 145 F.3d 1472, 47 U.S.P.Q.2d 1106 (Fed.Cir.1998); Hughes Aircraft Co. v. United States, 148 F.3d 1384, 47 U.S.P.Q.2d 1542 (Fed.Cir.1998).

Both Litton and Hughes II follow the Hughes I flexible bar approach to prosecution history estoppel. In that regard, they are consistent with Professor Chisum’s observation that “[mjost Federal Circuit panel decisions from 1984 to 1997 followed the flexible approach, which had been initiated in 1983 by the Hughes Aircraft[Hughes I ] decision.... ” Chisum, supra, § 18.05[3][b][i], at 18-497. Nevertheless, this court has neither repudiated Kinzen-baw nor reconciled the inconsistency- between the Hughes I and Kinzenbaw lines of authority.

Under these circumstances, it is unclear whether in any given case the court will apply the Kinzenbaw approach as opposed to the more generally accepted Hughes I approach. Just as importantly, even if the Hughes I approach is applied, there is uncertainty as to the extent of the surrender that will be held to exist. Thus, Professor Chisum has discussed two Federal Circuit cases, Sun Studs, Inc. v. ATA Equip. Leasing, Inc., 872 F.2d 978, 10 U.S.P.Q.2d 1338 (Fed.Cir.1989), and Environmental Instruments, Inc. v.

Sutron Corp., 877 F.2d 1561, 11 U.S.P.Q.2d 1132 (Fed.Cir.1989), as illustrating the “predictive difficulties of the flexible approach.” Chisum, supra, § 18.05[3][b][ii], at 18-505 to 18-506.

In a like vein, it has been stated that “the criteria used by the court to determine the effect of an estop-ping amendment have not been set forth in any clear or systematic way” and that “[t]he Federal Circuit’s well-known observation that ‘[djepending on the nature and purpose of an amendment, it may have a limiting effect from great to small to zero,’ for example, tells little about what the relationship is between the ‘nature and purpose’ of an amendment and its limiting effect.” Ted Apple, Enablement Estoppel: Should Prosecution History Estoppel Arise When Claims Are Amended To Overcome Enablement Rejections?, 13 Santa Clara Computer & High Tech L.

J. 107,128 (1997) (footnotes omitted). 3. Today, we revisit the question we first addressed in Hughes I and come to a different conclusion as to the proper scope of equivalents that is available when prosecution history estoppel applies than we did in that case. We hold that prosecution history estoppel acts as a complete bar to the application of the doctrine of equivalents when an amendment has narrowed the scope of a claim for a reason related to patentability.

Our decision to reject the flexible bar approach adopted in Hughes I comes after nearly twenty years of experience in performing our role as the sole court of appeals for patent matters. In those years, the notice function of patent claims has become paramount, and the need for certainty as to the scope of patent protection has been emphasized. A problem with the flexible bar approach is that it is virtually impossible to predict before the decision on appeal where the line of surrender is drawn.

The patentee would draw the line just at or slightly short of the prior art, leaving a wide range of equivalents untouched by prosecution history estoppel. The accused infringer, however, would draw the line close to the literal terms of the claims, leaving little or no range of equivalents. These considerations, we think, contribute to the difficulty under the flexible bar approach in predicting with any degree of certainty the scope of surrender that will be found when prosecution history estoppel applies.

In reaching our holding, we are mindful of the Supreme Court’s teaching that binding precedent is not to be lightly discarded. The Court has stated that stare deci-sis “promotes the evenhanded, predictable, and consistent development of legal principles, fosters reliance on judicial decisions and contributes to the actual and perceived integrity of the judicial process.” Payne v. Tennessee, 501 U.S. 808, 827, 111 S.Ct. 2597, 115 L.Ed.2d 720 (1991).

The Court also has stated that while from time to time it has overruled governing decisions that are “unworkable or are badly reasoned,” it has rarely done so “on grounds not advanced by the parties.” United States v. Int’l Bus. Machs. Corp., 517 U.S. 843, 856, 116 S.Ct. 1793, 135 L.Ed.2d 124 (1996) (citations omitted).

We believe that the current state of the law regarding the scope of equivalents that is available when prosecution history es-toppel applies is “unworkable.” In patent law, we think that rules qualify as “workable” when they can be relied upon to produce consistent results and give rise to a body of law that provides guidance to the marketplace on how to conduct its affairs. After our long experience with the flexible bar approach, we conclude that its “workability” is flawed.

Moreover, in overruling Hughes I, we are not acting “on grounds not advanced by the parties.” SMC and amici curiae have urged us to follow the strict approach to prosecution history es-toppel that we adopt today. In Banc Opening Br. of Defs.-Appellants SMC Corp., et al., at 49-53; see also Br. for Amici Curiae Int’l Bus. Machs. Corp., Eastman Kodak Co., and Ford Motor Co., at 14-20 (arguing that no range of equivalents should be available for narrowing claim amendments). We also believe that the flexible bar approach “poses a direct obstacle to the realization of important objectives.” Patterson v.

McLean Credit Union, 491 U.S. 164, 173, 109 S.Ct. 2363, 105 L.Ed.2d 132 (1989) (setting forth the “traditional justification[s] for overruling a prior case”). These objectives include giving effect, when prosecution history estoppel arises, to a narrowing amendment’s operation as a disclaimer of subject matter, see, e.g., Exhibit Supply, 315 U.S. at 136-37, 62 S.Ct. 513, preserving the notice function of patent claims, see, e.g., Warner-Jenkinson, 520 U.S. at 29, 117 S.Ct. 1040, and promoting certainty in patent law, see, e.g., Markman, 517 U.S. at 390, 116 S.Ct. 1384.

The realization of these objectives cannot help but be frustrated by the uncertainty inherent in the flexible bar approach. By making prosecution history estoppel act as a complete bar, we enforce the disclaimer effect of a narrowing claim amendment. By narrowing his claims, a patentee disclaims subject matter encompassed by the original claims.

E.g., Exhibit Supply, 315 U.S. at 136-37, 62 S.Ct. 513; Magic City Kennel Club, 282 U.S. at 790, 51 S.Ct. 291; Shepard, 116 U.S. at 598, 6 S.Ct. 493 (noting that a patentee who has narrowed a claim during prosecution cannot “enlarge her patent by argument so as to cover elements not falling within its terms, and which she had explicitly abandoned”).

As the Supreme Court has stated, “By amendment [the patentee] recognize[s] and emphasize[s] the difference between the” original claim and amended claim “and proclaim[s] ... abandonment of all that is embraced in that difference.” Exhibit Supply, 315 U.S. at 136, 62 S.Ct. 513. Amendments “must be strictly construed against the inventor and in favor of the public, and looked upon as in the nature of disclaimers.” Hubbell, 179 U.S. at 83-84, 21 S.Ct. 24.

In order to construe such amendments strictly against the patentee, no scope of equivalents can be afforded to a claim element that was narrowed because of patentability concerns. Although we do not understand older Supreme Court cases to have spoken directly to the question before us, we think the language used in those cases suggesting a strict measurement of the scope of equivalents is consistent with our answer to this question. Allowing some range of equivalents gives the patentee some benefit of the doubt as to what was disclaimed, a benefit that comes at the public’s expense.

A complete bar therefore best serves the notice and definitional function of patent claims. “The object of the patent law in requiring the patentee [to specifically define his invention] is 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, 12 S.Ct. 76, 35 L.Ed. 800 (1891). But “the doctrine of equivalents, when applied broadly, conflicts with the definitional and public-notice functions of the statutory claiming requirement.” Warner-Jenkinson, 520 U.S. at 29, 117 S.Ct. 1040.

If prosecution history estoppel acts as a complete bar to application of the doctrine of equivalents, both the patentee and the public are on notice as to the scope of protection provided by a claim element narrowed for a reason related to patenta-bility. The patentee and the public can look to the prosecution history, a public record, to determine if any prosecution history estoppel arises as to any claim element. If so, that element’s scope of protection is clearly defined by its literal terms.

The Supreme Court recognized the value of a complete bar in Warner-Jenkinson when it discussed the presumption that prosecution history estoppel applies when an amendment is unexplained. The Court, keeping in mind “that claims do indeed serve both a definitional and a notice function,” held that if the presumption was not rebutted, “prosecution history estoppel would bar the application of the doctrine [of] equivalents as to that element.” Id. at 33, 117 S.Ct. 1040 (emphasis added); see also infra Answer to En Banc Question 4.

A complete bar to the doctrine of equivalents for unexplained amendments would give, as the Court stated, “proper deference to the role of claims in defining an invention and providing public notice,” Warner-Jenkinson, 520 U.S. at 33, 117 S.Ct. 1040. A complete bar similarly serves the definitional and notice functions when explained amendments give rise to prosecution history estoppel.

Regardless of whether the amendment is explained or unexplained, if the amendment narrows the scope of the claim for a reason related to patentability, a complete bar to the doctrine of equivalents provides the public and the patentee with definite notice as to the scope of the claimed invention. A complete bar also eliminates the public’s need to speculate as to the subject matter surrendered by an amendment that narrows a claim for a reason related to patentability. There are several aspects of the prosecution history estoppel inquiry where speculation is not allowed.

The Supreme Court has noted that we need not inquire into the correctness of the examiner’s rejection that led to a claim amendment. Warner-Jenkinson, 520 U.S. at 33 n. 7, 117 S.Ct. 1040 (citing Magic City Kennel Club, 282 U.S. at 789-90, 51 S.Ct. 291). Even if the rejection is improper, the amendment may still give rise to prosecution history estoppel. Id. In addition, we do not speculate as to whether any given amendment was material to the prosecution of the patent because “[t]he patentee makes them all material by the restricted form of his claim.” Hubbell, 179 U.S. at 84, 21 S.Ct. 24 (citations omitted).

In view of the reluctance to entertain speculative inquiries in other aspects of prosecution history estoppel, a speculative inquiry should not be required to determine the scope of equivalents still available for a claim element narrowed for a reason related to patentability. A complete bar avoids such an inquiry. Under the flexible bar approach, however, the exact range of equivalents when prosecution history estoppel applies is virtually unascertainable, with only the prior art marking the outer limits of the claim’s scope.

There is no precise metric to determine what subject matter was given up between the original claim and the amended claim. Consider, for example, a claim that originally recited a value “less than twenty” that was amended to recite a value “less than five” in light of a rejection over prior art disclosing a value of fifteen. What subject matter was abandoned under the flexible approach? Is the patentee limited to values that are closer to five than fifteen, or can he reach any value less than fifteen?

Can the patentee encompass by equivalents a value of ten, or would that recapture part of the surrendered subject matter? Put simply, it is impossible, even under this basic example, for the public or the patentee to determine the precise range of equivalents available under the flexible bar approach. This creates a “zone of uncertainty which enterprise and experimentation may enter only at the risk of infringement claims ... [and which] discourage[s] invention only a little less than unequivocal foreclosure of the field.” Markman, 517 U.S. at 390, 116 S.Ct. 1384 (quoting United Carbon Co. v.

Binney & Smith Co., 317 U.S. 228, 236, 63 S.Ct. 165, 87 L.Ed. 232 (1942)). “The public [would] be deprived of rights supposed to belong to it, without being clearly told what it is that limits these rights.” Markman, 517 U.S. at 390, 116 S.Ct. 1384 (quoting Merrill v. Yeomans, 94 U.S. 568, 573, 24 L.Ed. 235 (1876)). A complete bar, unlike a flexible bar, thus lends certainty to the process of determining the scope of protection afforded by a patent.

With a complete bar, both the public and the patentee know that once an element of a claim is narrowed by amendment for a reason related to patent-ability, that element’s scope of coverage will not extend beyond its literal terms. There is no speculation or uncertainty as to the exact range of equivalents that might be available. This certainty aids both the public and the patentee in ascertaining the true scope and value of the patent without having to resort to litigation to obtain a case by case analysis of what subject matter the claims can cover.

With a complete bar, neither the public nor the patentee is required to pay the transaction costs of litigation in order to determine the exact scope of subject matter the patentee abandoned when the pat-entee amended the claim. Thus, under the complete bar approach, technological advances that would have lain in the unknown, undefined zone around the literal terms of a narrowed claim under the flexible bar approach will not go wasted and undeveloped due to fear of litigation.

The public will be free to improve on the patented technology and design around it without being inhibited by the threat of a lawsuit because the changes could possibly fall within the scope of equivalents left after a claim element has been narrowed by amendment for a reason related to patentability. This certainty will stimulate investment in improvements and design-arounds because the risk of infringement will be easier to determine.

In general, the difficulty in counseling the public and the patentee on the scope of protection provided by an amended element is greatly reduced under the complete bar approach due to the certainty and predictability such a bar produces. Finally, we see no overriding benefit to the flexible bar approach. Although a flexible bar affords the patentee more protection under the doctrine of equivalents, we do not believe that the benefit outweighs the costs of uncertainty.

The Supreme Court noted in Wamer-Jenkinson that the doctrine of equivalents has “taken on a life of its own, unbounded by the patent claims.” Warner-Jenkinson, 520 U.S. at 28-29, 117 S.Ct. 1040. A complete bar reins in the doctrine of equivalents, making claim scope more discernible and preserving the notice function of claims. The Court indicated that the application of a complete bar allowed prosecution history estoppel to place “reasonable limits on the doctrine of equivalents, and further insulate[ ] the doctrine from any feared conflict with the Patent Act.” Id.

The application of a complete bar to the doctrine of equivalents whenever a claim amendment gives rise to prosecution history estoppel similarly 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. D.

Question I When “no explanation [for a claim amendment] is established,” Warner-Jenkinson, 520 U.S. at 33, 117 S.Ct. 1040, thus invoking the presumption of prosecution history estoppel under Warner-Jenkinson, what range of equivalents, if any, is available under the doctrine of equivalents for the claim element so amended? We answer Question 4 as follows: When no explanation for a claim amendment is established, no range of equivalents is available for the claim element so amended.

This question is answered by Wamer-Jenkinson: Where no explanation is established, .... prosecution history estoppel would bar the application of the doctrine [of] equivalents as to that element. Warner-Jenkinson, 520 U.S. at 33, 117 S.Ct. 1040 (emphasis added). In answering this question, we affirm what we stated in Sextant, 172 F.3d at 832, 49 U.S.P.Q.2d at 1875: when “the Wamer-Jenkinson presumption is applicable, ... the prosecution history estoppel arising therefrom is total and completely ‘bars’ the application of the doctrine of equivalents as to the amended limitation.” E.

Question 5 Would a judgment of infringement in this case violate Wamer-Jenkinson’s requirement that the application of the doctrine of equivalents “is not allowed such broad play as to eliminate [an] element in its entirety,” 520 U.S. at 29, 117 S.Ct. 1040. In other words, would such a judgment of infringement, post Wamer-Jenkinson, violate the “all elements” rule? We do not need to reach this question for reasons which will become clear in our discussion of the specific case before us. Accordingly, we leave for another day any discussion of the “all elements” rule. IV.

Infringement of Festo’s Patents Festo is the owner by assignment of the Stoll patent and the Carroll patent, both of which are directed to magnetically coupled rodless cylinders. Festo sued SMC in the United States District Court for the District of Massachusetts, alleging infringement of the patents. The jury found that SMC infringed the Stoll patent under the doctrine of equivalents and assessed damages accordingly. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., No. 88-1814-PBS, slip op. at 2-3 (D.Mass. Oct. 27, 1994) (Judgment) (“Festo I (Judgment) ”).

The district court previously had granted Festo’s motion for

summary judgment that certain models of SMC’s rodless cylinders infringed the Carroll patent, also under the doctrine of equivalents. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., No. 88-1814-PBS, slip op. at 14-15 (D.Mass. July 11, 1994) (Order) (“Festo I (Order) ”). A. The Patents and Technology at Issue Both the Stoll patent and the Carroll patent disclose magnetic rodless cylinders. The claimed devices are composed of three basic parts: a piston, a cylinder, and a sleeve. In basic terms, the piston is on the inside of the cylinder, and is moved by fluid under pressure.

The sleeve is on the outside of the cylinder, and is magnetically coupled to the piston. The magnetic attraction between the sleeve and the piston causes the sleeve to follow the piston when it moves along the inside of the cylinder. The sleeve is used to move objects on a conveying system. 1. The application for the Stoll patent was filed on May 28, 1980; the patent issued on October 12, 1982. The following figure, the only drawing in the patent, shows the sleeve (18), the cylinder (10), and the piston (16) of the Stoll device: Inside the cylinder, the piston is driven by a pressurized fluid.

Stoll patent, col. 3, 11. 13-19. As the piston travels through the cylinder, the magnetically coupled sleeve follows the piston along the outside of the cylinder. Id. The piston includes magnets (20) and two “elastomeric sealing rings” (26). Id. at col. 3, 11. 20-32. The sealing rings prevent any impurities from getting on the piston. Id. at col. 3, 11. 48-55. There also are a pair of “guide rings” (24) on the piston. Id. at col. 3, 11. 26-30.

As the patent explains, the guide rings, which project beyond the piston’s surface, “pass along the internal [cylinder] surface in a sliding fit,” id. at col. 3,11. 29-30, and help prevent impurities from dirtying the piston, id. at col. 3,11. 51-55. The sleeve of the Stoll patent device is made of multiple parts that include magnets (32) and an outer body made of a magnetizable material (30). Id. at col. 3,11. 60-65.

According to the patent, the magnetizable material on the sleeve that encircles the sleeve’s magnets allows “magnetic leakage fields in the vicinity of the driven assembly to be kept to a minimum,” preventing any unwanted braking forces. Id. at col. 2,11. 24-35. Claim 1 of the Stoll patent is representative of the claims asserted by Festo, and is the only claim of the Stoll patent at issue on appeal: 1.

In an arrangement having a hollow cylindrical tube and driving and driven members movable thereon for conveying articles, the improvement comprising wherein said tube is made of a nonmagnetic material, wherein said driving member is a piston movably mounted on the inside of said tube, said piston having a piston body and plural axially spaced, first permanent annular magnets encircling said piston body, said piston further including first means spacing said first permanent magnets in said axial spaced relation, the radially peripheral surface of said magnets being oriented close to the internal wall surface of said tube, said piston further including plural guide ring means encircling said piston body and slidingly engaging said internal wall and first sealing rings located axially outside said guide rings for wiping said internal wall as said piston moves along said tube to thereby cause any impurities that may be present in said tube to be pushed along said tube so that said first annular magnets will be free of interference from said impurities, wherein said driven member includes a cylindrical sleeve made of a magnetizable material and encircles said tube, said sleeve having plural axially spaced second permanent annular magnets affixed thereto and in magnetically attracting relation to said first permanent annular magnets, and second means spacing said second permanent annular magnets in said axially spaced relation, the radially inner surface of said magnets being oriented close to the external surface of said tube, said sleeve having end face means with second sealing rings located axially outside said second permanent annular magnets for wiping the external wall surface of said tube as said driven member is moved along said tube in response to a driving movement of said piston to thereby cause any impurities that may be present on said tube to be pushed along said tube so that said second permanent annular magnets will be free of interference from said impurities.

Stoll patent, col. 5, 1. 23 — col. 6, 1. 18 (paragraphing added). 2. The application for the Carroll patent was filed on February 17, 1972; the patent issued on December 18, 1973. A reexamination certificate was issued on October 25, 1988, with amended claims. The Carroll patent is directed to the same technology as the Stoll patent.

An exterior view of the Carroll patent device is shown in Figure 1 of the Carroll patent, reproduced below: In the disclosed embodiment, the sleeve (28) is described as a permanent magnet that is attached to a gripping device (30) and that surrounds part of the exterior of the cylinder (10). Carroll patent, col. 2,11. 17-26. As in the device of the Stoll patent, the sleeve of the Carroll patent moves along the cylinder in response to a magnetic piston which moves inside the cylinder. Id. Each end of the piston has a sealing ring set in an annular groove. Id. at col. 2,11. 1-16.

According to the patent, the sealing rings “engage the inner wall of the cylinder and form a fluid tight seal” that allows compressed air, or any other pressurized fluid, injected into port (12) or (14) on the outside of the cylinder to move the piston in either direction. Id. at col. 2, 11. 10-16, 42-59. The polarization of the magnets on the piston and the sleeve causes the sleeve, which is located on the outside of the cylinder, to follow the movement of the piston, which is located on the inside of the cylinder. Id. at col. 2,11. 17-24.

Claim 9 of the reexamined Carroll patent is representative of the claims asserted by Festo: 9.

A device for moving articles, which comprises: a hollow cylinder formed of non-ferrous material and having opposite axial ends; a piston mounted in the interior of the hollow cylinder and reciproeatingly slid-able therein, the piston including a central mounting member disposed axially in the cylinder, a plurality of cylindrically-shaped permanent magnets mounted on the central mounting member and spaced apart axially from each other, each magnet having a bore formed axially there-through for receiving the central mounting member, at least one pair of end members mounted on the central mounting member and disposed on opposite axial sides of the plurality of magnets, a pair of cushion members formed of resilient material, the cushion members being situated near opposite axial ends of the central mounting member to help prevent damage to the piston when the piston contacts an axial end of the cylinder, and a pair of resilient sealing rings situated near opposite axial ends of the central mounting member and engaging the cylinder to effect a fluid-tight seal therewith; a body mounted on the exterior of the hollow cylinder and reciprocatingly slid-able thereon, the body including a plurality of annu-larly shaped permanent magnets surrounding the cylinder and spaced apart from each other, the permanent magnets of the piston and body being polarized so as to magnetically couple the body to the piston whereby movement of the piston inside the cylinder causes a corresponding movement of the body outside the cylinder, the body further including means provided thereon for holding on the body an

article to be moved; and means for controlling the admission of pressure fluid into the cylinder and exhaust fluid from the cylinder for moving the piston in the cylinder, the attractive forces between the permanent magnets of the piston and the body being such that movement of the piston causes corresponding movement of the body below a predetermined load on the body and such that above said predetermined load movement of the piston does not cause corresponding movement of the body. Reexamined Carroll patent, col.l, 1. 34— col. 2, 1. 37 (additional paragraphing added). 3.

The SMC devices that were found to infringe the Stoll and Carroll patents under the doctrine of equivalents have two notable differences from the structures claimed in the patents. First, the SMC devices, although having pistons with two hard plastic guide rings, have only a single resilient two-way sealing ring, located on one end of the pistons. Thus, while the patents disclose and claim devices with a pair of sealing rings, the SMC devices have only single two-way sealing rings.

Second, the outer portion of the sleeves of SMC’s devices is made of an aluminum alloy, a material that the parties agree is not a magnetizable material. Thus, while the Stoll patent discloses and claims a sleeve made of a magnetizable material, the SMC devices have sleeves that are not made of a magnetizable material. B. Prosecution History of the Patents at Issue 1. The Stoll patent application was filed in the United States as the U.S. counterpart of a German patent application. As filed, claim 1 of the Stoll patent initially read: 1.

A linear motor for use in a conveying system, said motor being operable by a pressure medium and comprising a tubular

part connectible to a source of the pressure medium, a piston which is slidable in said tubular part and which has sealing means at each end for [wjiping engagement with an internal surface of the tubular part and so as to form a seal for the pressure medium, and a driven assembly which is slida-ble on the tubular part and which has means at each end for [w]iping engagement with an external surface of the tubular part, the piston and the driven assembly each carrying a drive magnet arrangement in the form of a hollow cylindrical assembly, each magnet arrangement having radial play relative to the adjacent surface of the tubular part, and surfaces of the magnet arrangements which face the tubular part being closely adjacent to the respective surfaces of the tubular part.

The original application also included two dependent claims of relevance, claims 4 and 8: 4. A linear motor according to any of claims 1 to 3, wherein the sealing means of the piston comprise sealing rings and the piston is provided with sliding guide rings near the sealing rings. 8.

A linear motor according to any of the preceding claims wherein the driven assembly is provided with a sleeve made of a magentisable material, which encircles the hollow cylindrical assembly of the magnet arrangement. (Emphasis added.) In the first Office Action, the patent examiner rejected all twelve original claims, and cited three patents as references “believed pertinent.” Claims 1-12 were rejected under 35 U.S.C. § 112, ¶ 1, because the “exact method of operation is unclear.

Is [the] device a true motor or magnetic clutch?” In addition, claims 4-12 were rejected under 35 U.S.C. § 112, ¶ 2, because they were “improperly multiply dependent.” In response, Stoll amended some claims, including claim 1, and canceled others, including claims 4 and 8.

Claim 1 was amended to recite “plural guide ring means ... and first sealing rings located axially outside said guide rings” on the piston and to recite “a cylindrical sleeve made of a magnetizable material.” In the remarks accompanying the amendments, Stoll stated that “[e]ach of the claims now present in this application has been reviewed for compliance with the provisions of Title 35 U.S.C. § 112.

Accordingly, further consideration of these claims, particularly with respect to the provisions of Title 35 U.S.C. § 112, is respectfully solicited.” When Stoll submitted this amendment, he also made two German patents of record in the application, No. 27,37,924 and No. 19,82,379. Stoll had received these patents in the first office action in the corresponding German application. Stoll argued in the remarks accompanying the amendment that the “claims now present in th[e] application” are distinguishable over these references.

Stoll stated that “i[t] is clear that neither of these two references discloses the use of structure preventing the interference by impurities located inside the tube and on the outside of the tube while the arrangement is moved along the tube.” After considering this response, the examiner allowed the amended claims, requesting that all references to “linear motors” be deleted from the specification, because this phrase “connotes a different device having different operational characteristics.” 2. The relevant portion of the Carroll patent’s prosecution history is its reexamination.

Before reexamination, claim 1 of the Carroll patent read as follows: 1.

A device for moving articles comprising a cylinder of non-ferrous material, a piston including a permanent magnet having a pole-piece on each axial side thereof, a body disposed outside and adjacent to said cylinder, said body including a permanent magnet which substantially surrounds the cylinder, there being a pole piece on each axial side of the permanent magnet included in said body, and means for controlling the admission of pressure fluid into the cylinder and exhaust of fluid from the cylinder for moving the piston in the cylinder, the attractive forces between the permanent magnets being such that movement of the piston causes corresponding movement of the body below a predetermined load on the body and such that above said predetermined load movement of the piston does not cause corresponding movement of the body.

Original Carroll patent, col. 4, 11. 4-19 (paragraphing added). This claim did not recite the sealing rings disclosed in the specification. Carroll requested reexamination on March 18, 1988, citing German Patent No. 1,982,379, which was not of record in the Carroll patent’s prosecution history.

In his request for reexamination, Carroll asserted that the German patent presented a substantial new question of patentability because the Patent Office “may find the German patent, in combination with the other references which were cited during prosecution of the Carroll patent[,] ... to disclose several of the primary structural features of the device defined by Claim 1.” The German patent described rodless cylinders having several of the features of the device described in the Carroll patent, including a pair of sealing rings.

The Patent Office granted Carroll’s request for reexamination, finding that the German patent “discloses an

article transport device which is movable in response to a hydraulically operated magnetic piston, which is a feature that was not found by the Examiner during the prosecution” of the Carroll patent.

During reexamination, Carroll canceled claim 1 and added claim 9, which explicitly recites “a pair of resilient sealing rings situated near opposite axial ends of the central mounting member and engaging the cylinder to effect a fluid-tight seal therewith.” In the remarks accompanying the amendment, Carroll argued that the now-amended claims “more clearly and more specifically” define the “features of the patentee’s invention that distinguish over the art of record, including” the German patent cited in the request for reexamination.

Carroll also noted that the structure now described in claim 9 was not disclosed in the art of record. Carroll further stated that “the particular structure of the inner piston and outer body now specifically set forth in new claim 9 is not taught or suggested by the German patent,” particularly noting the recitation of the placement and plurality of magnets for both the piston and outer body and the recitation of resilient materials and cushion materials on the ends of the piston.

The examiner allowed the amended claims, stating that “the prior art does not teach or render obvious the claimed combination which includes the plurality of magnets, end members, and cushion members in the claimed relationship.” C. The District Court Proceedings Festo sued SMC in the district court for infringement of both the Stoll and Carroll patents. Festo’s claims of infringement and damages and SMC’s counterclaims of invalidity were referred to a special master for consideration. The special master determined that both the Stoll and Carroll patents were not invalid. Festo Corp. v.

Shoketsu Kinzoku Kogyo Kabushiki Co., No. 88-1814-MA, slip o

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