Court Opinion

ID: 9496430
Source: CourtListenerOpinion
Date Created: 2023-08-05 16:26:20.440723+00
Date Added: 2024-06-11T17:57:32.805950
License: Public Domain

Opinion for the court filed by Circuit Judge LOURIE, in which Circuit Judge MICHEL, Senior Circuit Judge PLAGER, and Circuit Judges CLEVENGER, RADER, SCHALL, BRYSON, GAJARSA, LINN, DYK, and PROST join.
Concurring opinion filed by Circuit Judge RADER. Opinion concurring in part and dissenting in part filed by Circuit Judge PAULINE NEWMAN, in which Chief Judge MAYER joins.
LOURIE, Circuit Judge.
This case is back to this court on remand from the Supreme Court of the United States for adjudication as to whether prosecution history estoppel bars Festo from relying on the doctrine of equivalents in this patent infringement suit. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 122 S.Ct. 1831, 152 L.Ed.2d 944 (2002) (“Festo VIII”). The sole issue specifically before us is whether Festo can rebut the presumption that the filing of narrowing amendments for the two patents in suit surrendered all subject matter between the original claim limitations and the amended claim limitations. Id. at 741, 122 S.Ct. 1831. For the reasons set forth herein, we conclude that Festo cannot overcome that presumption by demonstrating that the rationale underlying the narrowing amendments bore no more than a tangential relation to the accused equivalents or by demonstrating that there was “some other reason” such that the patentee could not reasonably *1364have been expected to have described the accused equivalents. However, we remand to the district court to determine whether Festo can rebut the presumption of surrender by establishing that the equivalents in question would have been unforeseeable to one of ordinary skill in the art at the time of the amendments.
BACKGROUND
Enough has been written about the facts and prior decisions in this case that we need not provide more than a brief summary here. This litigation began in 1988 when Festo filed suit against Shoketsu Kinzoku Kogyo Kabushiki Co. and SMC Pneumatics, Inc. (collectively, “SMC”) for infringement of United States Patents 4,354,125 (the “Stoll patent”) and B1 3,779,401 (the “Carroll patent”), which relate to magnetically coupled rodless cylinders. The United States District Court for the District of Massachusetts granted partial summary judgment that SMC’s accused device infringed claims 5, 6, and 9 of the Carroll patent under the doctrine of equivalents, and a jury found that SMC’s accused device infringed claim 1 of the Stoll patent under the doctrine of equivar lents. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., No. 88-1814-PBS (D.Mass. Oct. 27,1994) (“Festo I”).
After initially affirming the district court’s judgment, Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 72 F.3d 857 (Fed.Cir.1995) (“Festo II”), vacated and remanded, 520 U.S. 1111, 117 S.Ct. 1240, 137 L.Ed.2d 323 (1997) (“Festo III”),1 we eventually took the case en banc to address certain issues relating to prosecution history estoppel and 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). Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 234 F.3d 558, 563 (Fed.Cir.2000) (en banc) (“Festo VI”). In our en banc decision, we held that: (1) a “substantial reason related to patentability” that may give rise to an estoppel is not limited to overcoming prior art under 35 U.S.C. § 102 or § 103, but encompasses other reasons relating to the statutory requirements for a patent, including compliance with 35 U.S.C. § 112, id. at 566; (2) a “voluntary” claim amendment — i.e., one neither required by a patent examiner nor made in response to a rejection by an examiner for a stated reason — may give rise to prosecution history estoppel, id. at 568; (3) no range of equivalents is available for an amended claim limitation when prosecution history estop-pel applies, id. at 569; and (4) “unexplained” amendments are not entitled to any range of equivalents, id. at 578 (citing Warner-Jenkinson, 520 U.S. at 33, 117 S.Ct. 1040). Applying those principles to the facts of this case, we concluded that the limitations at issue in the Stoll and Carroll patents had been narrowed by amendments made during prosecution and reexamination, respectively, and that Fes-to had failed to establish reasons unrelated to patentability for those amendments. Id. at 587-91. We therefore held that no range of equivalents was available for the amended claim limitations and reversed the district court’s judgment of infringement with respect to both patents. Id. at 588-91.
*1365The Supreme Court then granted certio-rari to review our en banc decision. Festo Corp. v. Shoketsu Kinzoku Kogyo Kdbushiki Co., 583 U.S. 915, 121 S.Ct. 2519, 150 L.Ed.2d 692 (2001) (“Festo VII”). First, the Court agreed with our holding that “a narrowing amendment made to satisfy any requirement of the Patent Act may give rise to an estoppel.” Festo VIII, 535 U.S. at 736, 122 S.Ct. 1831. Second, however, the Court disagreed with our adoption of a complete bar to the doctrine of equivalents when prosecution history estoppel arises. Id. at 737, 122 S.Ct. 1831. The Court instead established a presumption that a narrowing amendment made for a reason of patentability surrenders the entire territory between the original claim limitation and the amended claim limitation, and explained that a patentee may overcome that presumption by showing that “at the time of the amendment one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent.” Id. at 741, 122 S.Ct. 1831. Specifically, the Court enumerated the three ways in which the patentee may overcome the presumption — i.e., by demonstrating that “the equivalent [would] have been unforeseeable at the time of the [amendment],”2 that “the rationale underlying the amendment [bore] no more than a tangential relation to the equivalent in question,” or that “there [was] some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question.” Id. at 740-41, 122 S.Ct. 1831. Observing that the narrowing amendments at issue in this case were made for reasons of patentability, the Court remanded for this court or the district court to determine in the first instance whether Festo can demonstrate that those narrowing amendments did not surrender the particular equivalents in question. Id. The Court accordingly vacated and remanded the judgment of our en banc court. Id. at 742, 122 S.Ct. 1831.
On remand, we asked the parties to brief the following issues:
1. Whether rebuttal of the presumption of surrender, including issues of foreseeability, tangentialness, or reasonable expectations of those skilled in the art, is a question of law or one of fact; and what role a jury should play in determining whether a patent owner can rebut the presumption.
2. What factors are encompassed by the criteria set forth by the Supreme Court.
3. If a rebuttal determination requires factual findings, then whether, in this case, remand to the district court is necessary to determine whether Festo can rebut the presumption that any narrowing amendment surrendered the equivalent now asserted, or whether the record as it now stands is sufficient to make those determinations.
4. If remand to the district court is not necessary, then whether Festo can rebut the presumption that any narrowing amendment sur*1366rendered the equivalent now asserted.
Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 304 F.3d 1289, 1290-91 (Fed.Cir.2002) (order). We received briefs from the parties and fifteen amici curiae, and we heard oral argument on these issues.
DISCUSSION
A. Reinstatement of Our Undisturbed En Banc Holdings
Before addressing the four issues briefed by the parties, we first take this opportunity to tie up the loose ends concerning our now-vacated holdings on the subject of prosecution history estoppel. Although, as a technical matter, our earlier en banc decision was vacated and we are free to revisit our prior conclusions, we reinstate those holdings of Festo VI that were not disturbed by the Supreme Court. To begin with, we recognize that the Court expressly endorsed our holding that a narrowing amendment made to comply with any provision of the Patent Act, including § 112, may invoke an estoppel. Festo VIII, 535 U.S. at 736, 122 S.Ct. 1831; see also Festo VI, 234 F.3d at 566.
We next reinstate our holding that a “voluntary” amendment may give rise to prosecution history estoppel. Festo VI, 234 F.3d at 568. That separate holding was not considered, and certainly was not rejected, by the Supreme Court. See Festo VIII, 535 U.S. at 727-28, 122 S.Ct. 1831. Moreover, it is consistent with the Court’s remand, and its reinstatement confirms what we have already determined by an overwhelming 11-1 majority.
In addition, we clarify that the Supreme Court’s Warner-Jenkinson presumption, which treats a narrowing amendment as having been made for a “substantial reason related to patentability” when the record does not reveal the reason for the amendment, 520 U.S. at 33, 117 S.Ct. 1040, remains intact after the Court’s Festo decision, although the consequences of failing to overcome that presumption have been altered. In Festo VI, we held that such an “unexplained” amendment completely estops a patentee from relying on the doctrine of equivalents for the narrowed claim limitation. 234 F.3d at 578. Although the Supreme Court rejected that “complete bar” approach, it confirmed that a patentee’s failure to overcome the Warner-Jenkinson presumption gives rise to the new Festo presumption of surrender. Festo VIII, 535 U.S. at 740, 122 S.Ct. 1831 (“[W]hen the court is unable to determine the purpose underlying a narrowing amendment—and hence a rationale for limiting the estoppel to the surrender of particular equivalents—the court should presume that the patentee surrendered all subject matter between the broader and the narrower language.”). A patentee is now entitled to rebut the presumption that an “unexplained” narrowing amendment surrendered the entire territory between the original and the amended claim limitations.
Thus, the Warner-Jenkinson and Festo presumptions operate together in the following manner: The first question in a prosecution history estoppel inquiry is whether an amendment filed in the Patent and Trademark Office (“PTO”) has narrowed the literal scope of a claim. Pioneer Magnetics, Inc. v. Micro Linear Corp., 330 F.3d 1352, 1356 (Fed.Cir.2003). If the amendment was not narrowing, then prosecution history estoppel does not apply. But if the accused infringer establishes that the amendment was a narrowing one, then the second question is whether the reason for that amendment was a substantial one relating to patenta-bility. See id. When the prosecution his*1367tory record reveals no reason for the narrowing amendment, Warner-Jenkinson presumes that the patentee had a substantial reason relating to patentability; consequently, the patentee must show that the reason for the amendment was not one relating to patentability if it is to rebut that presumption. See id. (citing Warner-Jenkinson, 520 U.S. at 33, 117 S.Ct. 1040). In this regard, we reinstate our earlier holding that a patentee’s rebuttal of the Warner-Jenkinson presumption is restricted to the evidence in the prosecution history record. Festo VI, 234 F.3d at 586 & n. 6; see also Pioneer Magnetics, 330 F.3d at 1356 (stating that only the prosecution history record may be considered in determining whether a patentee has overcome the Warner-Jenkinson presumption, so as not to undermine the public notice function served by that record). If the patentee successfully establishes that the amendment was not for a reason of patent-ability, then prosecution history estoppel does not apply.
If, however, the court determines that a narrowing amendment has been made for a substantial reason relating to patentability — whether based on a reason reflected in the prosecution history record or on the patentee’s failure to overcome the Warner-Jenkinson presumption — then the third question in a prosecution history es-toppel analysis addresses the scope of the subject matter surrendered by the narrowing amendment. See Pioneer Magnetics, 330 F.3d at 1357. At that point Festo VIII imposes the presumption that the patentee has surrendered all territory between the original claim limitation and the amended claim limitation. See Festo VIII, 535 U.S. at 740, 122 S.Ct. 1831. The patentee may rebut that presumption of total surrender by demonstrating that it did not surrender the particular equivalent in question according to the criteria discussed below. Finally, if the patentee fails to rebut the Festo presumption, then prosecution history estoppel bars the patentee from relying on the doctrine of equivalents for the accused element. If the patentee successfully rebuts the presumption, then prosecution history estoppel does not apply and the question whether the accused element is in fact equivalent to the limitation at issue is reached on the merits.
B. The Roles of the Judge and Jury
We turn now to resolution of the four issues that we asked the parties to brief after the Supreme Court’s remand. In response to our first question regarding the proper roles of the judge and jury, Festo submits that, although the ultimate question whether prosecution history es-toppel applies may be a question of law, rebuttal of the presumption of surrender is a question of fact with underlying factual issues that should be determined by a jury. In contrast, SMC posits that rebuttal of the presumption of surrender is a question of law for the court to decide and one in which a jury has no role to play.
We agree with SMC that rebuttal of the presumption of surrender is a question of law to be determined by the court, not a jury. Prosecution history estoppel has traditionally been viewed as equitable in nature, its application being “guided by equitable and public policy principles.” Loctite Corp. v. Ultraseal Ltd., 781 F.2d 861, 871 n. 7 (Fed.Cir.1985), overruled on other grounds by Nobelpharma AB v. Implant Innovations, Inc., 141 F.3d 1059, 1068 (Fed.Cir.1998); see Black & Decker, Inc. v. Hoover Serv. Ctr., 886 F.2d 1285, 1295 (Fed.Cir.1989); Builders Concrete, Inc. v. Bremerton Concrete Prods. Co., 757 F.2d 255, 258 (Fed.Cir.1985). We have stated on numerous occasions that whether prosecution history estoppel applies, and hence whether the doctrine of equivalents *1368may be available for a particular claim limitation, presents a question of law. E.g., Bai v. L & L Wings, Inc., 160 F.3d 1350, 1364 (Fed.Cir.1998); Cybor Corp. v. FAS Techs., Inc., 138 F;3d 1448, 1460 (Fed.Cir.1998) (en banc). .The Supreme Court has recognized that, as a legal limitation on the application of the doctrine of equivalents, prosecution history estoppel is a matter to be determined by the court. Warner-Jenkinson, 520 U.S. at 39 n. 8, 117 S.Ct. 1040; see also Multiform Desiccants, Inc. v. Medzam, Ltd., 133 F.3d 1473, 1480 (Fed. Cir.1998) (“The court determines .'.. whether there is any estoppel derived from the prosecution history that bars remedy even when there is technologic equivalency-”). Questions relating to the application and scope of prosecution history estoppel thus fall within the exclusive province of the court. Accordingly, the determinations concerning whether the presumption of surrender has arisen and whether it has been rebutted are questions of law for the court, not a jury, to decide.3
C. Rebuttal of the Festo Presumption
In response to our second question, the parties' and several amici propose a variety of factors that they argue ought to be encompassed by the Supreme Court’s test for rebuttal; other amici, including the United States, suggest that we should refrain from identifying such factors at this time and instead should address the relevant factors as they arise in future cases. In addition, the parties offer divergent views as to what evidence a court should consider in determining whether a paten-tee has rebutted the presumption of surrender. On the one hand, Festo submits that the district court should be permitted to consider any relevant evidence, whether documentary or testimonial, in evaluating rebuttal of the presumption. On the other hand, SMC argues that the court’s evaluation of a patentee’s rebuttal should be based on the prosecution history record.
In discussing its newly established presumption, the Supreme Court made clear that the patentee bears the burden of showing that a narrowing amendment did not surrender a particular equivalent and explained that a patentee may rebut the presumption of surrender by showing that “at the time of the amendment one skilled in the art could not reasonably be expected to have drafted a claim that would have literally encompassed the alleged equivalent.” Festo VIII, 535 U.S. at 741, 122 S.Ct. 1831. As indicated above, the Court identified the three ways in which the pat-entee may overcome the presumption. Specifically, the patentee must demonstrate that the alleged equivalent would have been unforeseeable at the time of the narrowing amendment, that the rationale underlying the narrowing amendment bore no more than a tangential relation to the equivalent in question, or that there was “some other reason” suggesting that the patentee could not reasonably have been expected to have described the alleged equivalent. Id. at 740-41, 122 S.Ct. 1831. Because we cannot anticipate all of the circumstances in which a patentee might rebut the presumption of surrender, we believe that discussion of the relevant factors encompassed by each of the rebuttal criteria is best left to development on a case-by-case basis. However, we provide the following general guidance, which we apply to the patents in suit below, regard*1369ing the application of the three rebuttal criteria.
The first criterion requires a paten-tee to show that an alleged equivalent would have been “unforeseeable at the time of the amendment and thus beyond a fair interpretation of what was surrendered.” Id. at 738, 122 S.Ct. 1831. This criterion presents an objective inquiry, asking whether the alleged equivalent would have been unforeseeable to one of ordinary skill in the art at the time of the amendment. Usually, if the alleged equivalent represents later-developed technology {e.g., transistors in relation to vacuum tubes, or Velcro® in relation to fasteners) or technology that was not known in the relevant art, then it would not have been foreseeable. In contrast, old technology, while not always foreseeable, would more likely have been foreseeable. Indeed, if the alleged equivalent were known in the prior art in the field of the invention, it certainly should have been foreseeable at the time of the amendment. See Pioneer Magnetics, 330 F.3d at 1357. By its very nature, objective unforeseeability depends on underlying factual issues relating to, for example, the state of the art and the understanding of a hypothetical person of ordinary skill in the art at the time of the amendment. Therefore, in determining whether an alleged equivalent would have been unforeseeable, a district court may hear expert testimony and consider other extrinsic evidence relating to the relevant factual inquiries.
The second criterion requires a patentee to demonstrate that “the rationale underlying the narrowing amendment [bore] no more than a tangential relation to the equivalent in question.” Festo VIII, 535 U.S. at 740, 122 S.Ct. 1831. In other words, this criterion asks whether the reason for the narrowing amendment was peripheral, or not directly relevant, to the alleged equivalent. See The American Heritage College Dictionary 1385 (3d ed.1997) (defining “tangential” as “[m]erely touching or slightly connected” or “[o]nly superficially relevant; divergent”); 2 The New Shorter Oxford English Dictionary 3215-16 (1993) (defining “tangential” as “merely touching] a subject or matter; peripheral”). Although we cannot anticipate the instances of mere tangentialness that may arise, we can say that an amendment made to avoid prior art that contains the equivalent in question is not tangential; it is central to allowance of the claim. See Pioneer Magnetics, 330 F.3d at 1357. Moreover, much like the inquiry into whether a patentee can rebut the Warner-Jenkinson presumption that a narrowing amendment was made for a reason of pat-entability, the inquiry into whether a pat-entee can rebut the Festo presumption under the “tangential” criterion focuses on the patentee’s objectively apparent reason for the narrowing amendment. As we have held in the Warner-Jenkinson context, that reason should be discernible from the prosecution history record, if the public notice function of a patent and its prosecution history is to have significance. See id. at 1356 (“Only the public record of the patent prosecution, the prosecution history, can be a basis for [the reason for the amendment to the claim]. Otherwise, the public notice function of the patent record would be undermined.”); Festo VI, 234 F.3d at 586 (“In order to give due deference to public notice considerations under the Warner-Jenkinson framework, a patent holder seeking to establish the reason for an amendment must base his arguments solely upon the public record of the patent’s prosecution, i.e., the patent’s prosecution history. To hold otherwise— that is, to allow a patent holder to rely on evidence not in the public record to establish a reason for an amendment — would *1370undermine the public notice function of the patent record.”)- Moreover, whether an amendment was merely tangential to an alleged equivalent necessarily requires focus on the context in which the amendment was made; hence the resort to the prosecution history. Thus, whether the patentee has established a merely tangential reason for a narrowing amendment is for the court to determine from the prosecution history record without the introduction of additional evidence, except, when necessary, testimony from those skilled in the art as to the interpretation of that record.
The third criterion requires a patentee to establish “some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question.” Festo VIII, 585 U.S. at 741, 122 S.Ct. 1881. This category, while vague, must be a narrow one; it is available in order not to totally foreclose a patentee from relying on reasons, other than unforeseeability and tan-gentialness, to show that it did not surrender the alleged equivalent. Thus, the third criterion may be satisfied when there was some reason, such as the shortcomings of language, why the patentee was prevented from describing the alleged equivalent when it narrowed the claim. When at all possible, determination of the third rebuttal criterion should also be limited to the prosecution history record. For example, as we recently held in Pioneer Mag-netics, Inc. v. Micro Linear Corp., 330 F.3d 1352 (Fed.Cir.2003), a patentee may not rely on the third rebuttal criterion if the alleged equivalent is in the prior art, for then “there can be no other reason the patentee could not have described the substitute in question.” Id. at 1357. We need not decide now what evidence outside the prosecution history record, if any, should be considered in determining if a patentee has met its burden under this third rebuttal criterion.4
D. The Patents in Suit
Having set forth the general legal standards that govern rebuttal of the presumption of surrender, we turn now to Festo’s attempt to overcome that presumption with respect to the Stoll and Carroll patents. In response to our third and fourth questions, Festo argues that remand to the district court is necessary in this case so that it may develop the record according to the Supreme Court’s newly created rebuttal criteria. Festo maintains that it will present documentary and testimonial evidence to demonstrate that the narrowing amendments to the Stoll and Carroll patents did not surrender the two equivalents in question. In contrast, SMC argues that further remand is not necessary because, as a matter of law, Festo cannot rebut the presumption of surrender with respect to either accused equivalent.
Based on the parties’ arguments and the prosecution history record, we conclude that Festo cannot show that the “magnetizable” and “sealing ring” amendments to the Stoll and Carroll patents were “tangential” or were made for “some other reason.” However, because there exist factual issues relating to the objective un-*1371foreseeability of the two accused equivalents, we remand to the district court to determine whether Festo can rebut the presumption of surrender by demonstrating that the accused device’s aluminum sleeve and sealing ring elements would have been unforeseeable to a person of ordinary skill in the art at the time of the amendments.
1. SMC’s Aluminum Sleeve
Claim 1 of the application that issued as the Stoll patent originally recited a linear motor having a piston, a driven assembly, and a magnet arrangement. Stoll amended that claim during prosecution by, inter alia, adding the limitation that the driven member include “a cylindrical sleeve made of a magnetizable material.” '125 patent, col. 6, 11. 2-3 (emphasis added). Because that narrowing amendment was made for a reason of patentability, see Festo VIII, 535 U.S. at 741, 122 S.Ct. 1831, Stoll presumptively disclaimed the entire territory between the original limitation and the amended limitation, i.e., any driven member that does not have “a cylindrical sleeve made of a magnetizable material.” SMC’s accused device includes a sleeve made of aluminum, a nonmagnetizable material. Thus, the question before us is whether Festo can show that the “magnetizable” amendment did not surrender an aluminum sleeve.5
First, we are unable to determine whether Festo can satisfy the first rebuttal criterion on the current record. Although it seems unlikely that an aluminum sleeve would have been unforeseeable, as it was made of a commonly available metal, Festo argues that one skilled in the art at the time of the “magnetizable” amendment would not have foreseen the interchangeability of an aluminum alloy sleeve and a magnetizable alloy sleeve in Stoll’s small gap design involving rare earth magnets. Factual issues thus exist as to whether an ordinarily skilled artisan would have thought an aluminum sleeve to be an unforeseeable equivalent of a magnetizable sleeve in the context of the invention. Accordingly, we remand to the district court on the question of unforeseeability to allow the parties to introduce evidence on this issue.
Second, however, we conclude that Festo has failed to show that the reason for the “magnetizable” amendment was only tangentially related to SMC’s aluminum sleeve. Festo argues that the original claims in the Stoll patent were rewritten as a single independent claim in response to a § 112, ¶ 1 rejection, in which the examiner questioned whether the invention was a motor or a clutch, and that the “magnetizable” limitation was unnecessary to answer that question. Festo thus argues that the amendment was unnecessary to respond to (and thus only tangential to) the § 112 rejection; however, it fails to explain how the patentee’s rationale for adding the term “magnetizable” was only tangential, or peripheral, to the accused equivalent of a nonmagnetizable aluminum sleeve. Because the prosecution history reveals no reason for the *1372“magnetizable” amendment, Festo VI, 234 F.3d at 588, and because Festo still identifies no such reason, Festo has not shown that the rationale for the “magnetizable” amendment was only tangential to the accused equivalent. We therefore conclude that Festo cannot satisfy the “tangential” criterion for the aluminum sleeve equivalent.
Third, we conclude that Festo has pointed to no “other” reason why the pat-entee could not reasonably have been expected to have described an aluminum sleeve. Festo argues that it can satisfy the third rebuttal criterion by showing that Stoll could not reasonably have been expected to have drafted a claim to cover what was thought to be an inferior and unacceptable design. That argument does not help Festo in satisfying the “other” criterion; indeed, it suggests that Stoll could have described an aluminum sleeve but chose not to do so because that “inferi- or” element was not a part of his invention. In any event, it seems clear that there was no linguistic or “other” limitation to prevent Stoll from describing the accused equivalent. Although Stoll chose to claim a “magnetizable” sleeve, he reasonably could have been expected to have described a sleeve made of a common non-magnetizable material, such as aluminum, if that were what he intended to claim. For example, Stoll could have described the accused equivalent at various levels of specificity by using a common descriptive term such as “aluminum” or “metal.” We therefore conclude that Festo cannot satisfy the third rebuttal criterion for the aluminum sleeve equivalent.
2. SMC’s Sealing Ring
Both the Stoll patent and the Carroll patent include “sealing ring” limitations that were added by amendments made in the PTO. With respect to the Stoll patent, claim 1 of the original application recited a linear motor that included a piston having “sealing means at each end.” In response to an examiner’s rejection during prosecution, Stoll amended claim 1 to recite “first sealing rings” and “second sealing rings.” '125 patent, col. 5, 1. 37 & col. 6, 1. 11. It must therefore be presumed that Stoll surrendered all “sealing means” other than two-ring structures. With respect to the Carroll patent, claim 1 of the original application made no reference to sealing rings. During reexamination, however, Festo (as assignee of the Carroll patent) amended claim 1 (as new claim 9) to require “a pair of resilient sealing rings.” '401 patent, col. 2, 1. 14. Because that narrowing amendment was made for a reason of patentability, see Festo VIII, 535 U.S. at 741, 122 S.Ct. 1831, Festo presumptively disclaimed devices that include other than two sealing rings. SMC’s accused device includes a single two-way sealing ring. Thus, the question before us is whether Festo can demonstrate that the two “sealing ring” amendments did not surrender a single two-way sealing ring.
First, we cannot determine from the current record whether the accused sealing ring element would have been objectively unforeseeable at the time of the amendments. Festo argues that SMC’s two-way sealing ring was an inferior and unforeseeable equivalent of the one-way sealing rings located at each end of the piston in the claimed invention. Factual issues thus exist as to whether a person of ordinary skill in the art would have considered the accused two-way sealing ring to be an unforeseeable equivalent of the recited pair of sealing rings. We therefore remand to the district court to determine, with' the presentation of evidence as the court sees fit, the objective unforeseeability of a single two-way sealing ring.
*1373Second, however, we conclude that Festo has not shown that the rationales underlying the “sealing ring” amendments were only tangentially related to a single two-way sealing ring. Festo argues that the “sealing ring” amendment in the Stoll patent was made to clarify the invention in response to a § 112 rejection, and that the amendment in the Carroll patent could not have distinguished the prior art based on the relevant aspect of the invention because the prior art disclosed a pair of sealing rings. Looking to the prosecution history, however, we earlier concluded that the “sealing ring” amendments in both the Stoll patent and the Carroll patent were made to distinguish prior art patents. With respect to the Stoll patent, we determined that the “sealing ring” amendment was made' to distinguish two prior art patents that did not disclose sealing rings. Festo VI, 234 F.3d at 589 (“[NJeither of [the two prior art patents] 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.”). Similarly, with respect to the Carroll patent, we stated that, even though a prior art patent disclosed a piston with sealing rings, Festo distinguished that reference by claiming a combination of features that included a pair of sealing rings. Id. at 591. Thus, we have already determined that the two “sealing ring” amendments were made to distinguish prior art patents based, at least in part, on the “sealing ring” aspect of the invention. Nothing in the prosecution history or the Supreme Court’s opinion has changed the soundness of those determinations. We therefore conclude that Festo cannot establish that the rationales underlying the “sealing ring” amendments were only tangentially related to SMC’s accused sealing ring.
Third, we conclude that Festo has not established some “other” reason that the patentees could not reasonably have been expected to have described a single two-way sealing ring. Festo again argues that it can satisfy the third rebuttal criterion by showing that the patentees could not reasonably have been expected to have drafted claims to cover an inferior and unacceptable design. We again reject that argument as unpersuasive because, if the patentees knew of an inferior design and chose not to include it within the claims, then it cannot be said that they could not have been expected to have described that design. Festo also argues that it would have been unreasonable to have expected Stoll to have broadened the original claim to cover the accused equivalent. Festo’s premise — that the original claim did not encompass an equivalent two-way sealing ring — is in error, however. It overlooks our earlier conclusion, which we ratify here, that the original “sealing means” limitation literally encompassed structural equivalents under § 112, ¶ 6. Id. at 589. Therefore, SMC’s single two-way sealing ring, if in fact equivalent, would have fallen within the literal scope of the original claim, and Festo’s argument cannot succeed. More to the point, it cannot be said that there was a linguistic or “other” limitation preventing Stoll and Festo from describing the equivalent in question, especially where, as here, the difference between the claimed limitation and the accused equivalent is principally a difference in quantity. Instead of reciting “first sealing means ... and second sealing means” or “a pair of ... sealing rings,” the patentees easily could have encompassed SMC’s sealing ring by claiming, for example, “at least one sealing ring.” We therefore conclude that Festo cannot rebut the presumption that Stoll and Festo surrendered a single two-way *1374sealing ring under the third rebuttal criterion.
E. Remand
On remand, both parties may introduce evidence relating to the unforeseeability of the equivalents in question, as the trial court deems appropriate. If the court determines that Festo has failed to rebut the presumption of surrender, then prosecution history estoppel bars Festo from relying on the doctrine of equivalents. If, however, the court determines that Festo has successfully rebutted the presumption with respect to either of the two accused equivalents, then the court may reinstate its and the jury’s findings regarding equivalency in fact, as appropriate.
CONCLUSION
For the foregoing reasons, we conclude that Festo cannot overcome the presumption of surrender by showing that the narrowing amendments to the “magnetizable” and “sealing ring” limitations of the Stoll and Carroll patents were only “tangential” or were made for “some other reason.” However, we remand to the district court to consider whether Festo can rebut the presumption by demonstrating that the two accused equivalents would have been unforeseeable to a person of ordinary skill in the art at the time of the amendments.

REMANDED.

. On a first remand from the Supreme Court, a panel of this court again affirmed the district court’s judgment of infringement under the doctrine of equivalents. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 172 F.3d 1361 (Fed.Cir.1999) ("Festo IV"). We then granted SMC’s petition for rehearing en banc. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 187 F.3d 1381 (Fed.Cir.1999) ("Festo V”).

. The Supreme Court referred to unforesee-ability both at the “time of the amendment” and at the "time of the application.” Festo VIII, 535 U.S. at 738, 741, 122 S.Ct. 1831. We. clarify that the time when the narrowing amendment was made, and not when the application was filed, is the relevant time for evalúating unforeseeability, for that is when the patentee presumptively surrendered the subject matter in question and it is at that time that foreseeability is relevant. See Pioneer Magnetics, Inc. v. Micro Linear Corp., 330 F.3d 1352, 1357 (Fed.Cir.2003).

. We recognize that rebuttal of the presumption may be subject to underlying facts, which we discuss in more detail below. Nonetheless, the resolution of factual issues underlying a legal question may properly be decided by the court, See, e.g., Markman v. Westview Instruments, Inc., 52 F.3d 967, 980-81 (Fed. Cir.1995) (en banc), aff'd, 517 U.S. 370, 390, 116 S.Ct. 1384, 134 L.Ed.2d 577 (1996) (claim construction).

. Consistent with Supreme Court precedent, the holdings of that Court and our own regarding the Festo presumption of surrender and its rebuttal apply to all granted patents and to all pending litigation that has not been concluded with a final judgment, including appeals. See Harper v. Va. Dep't of Taxation, 509 U.S. 86, 97, 113 S.Ct. 2510, 125 L.Ed.2d 74 (1993) (“When this Court applies a rule of federal law to the parties before it, that rule is the controlling interpretation of federal law and must be given full retroactive effect in all cases still open on direct review and as to all events, regardless of whether such events predate or postdate our announcement of the rule.").

. SMC argues that Festo is completely barred from relying on the doctrine of equivalents for the "magnetizable” amendment because that amendment was “unexplained.” However, as discussed above, an "unexplained” amendment — -just like a narrowing amendment made for a reason of patentability — triggers a rebuttable presumption that the patentee has surrendered the entire territory between the original and the amended limitations. See Festo VIII, 535 U.S. at 740, 122 S.Ct. 1831. Festo is thus entitled to attempt to rebut the presumption of surrender for the "magnetizable” amendment. In any event, the Supreme Court made clear that the "magnetizable” amendment gives rise to the Festo presumption of surrender. See id. at 741, 122 S.Ct. 1831.