• The New FESTO Rules: Determining Limitations on the Doctrine of Equivalents Due to Prosecution History Estoppel
  • October 21, 2003
  • Law Firm: Piper Rudnick LLP - Washington Office
  • On September 26, 2003, the Court of Appeals for the Federal Circuit, sitting en banc, handed down its most recent decision1 in the Festo line of cases, pursuant to a remand from the Supreme Court last spring.2 The central issue in the Festo line of cases is the proper analysis to be used in the application of the "doctrine of equivalents" in determining patent infringement, when the claims of a patent were narrowed by amendment in the Patent Office. The federal circuit's most recent decision elaborates upon the Supreme Court's decision last year, setting forth a detailed analysis to be made in determining when the rule of "prosecution history estoppel" may arise to limit the use of the doctrine of equivalents in establishing patent infringement.


    The doctrine of equivalents generally provides that even if elements of an accused device do not fall within the literal language of a patent claim, the device may nevertheless infringe if the device elements are "equivalent" to those claimed. The determination of what is "equivalent" to a claim element, not surprisingly, often introduces complexity into litigation and infringement analysis generally. Part of this complexity arises from the application of the rule of prosecution history estoppel, which provides that amendments and arguments made in the Patent Office may be used to limit the scope of the claims of a patent. Such amendments and arguments may bar the patentee from asserting that an accused device is an equivalent of the claimed invention. In Warner-Jenkinson v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), the Supreme Court held that any narrowing amendment made for a "substantial reason related to patentability" creates a rebuttable presumption that prosecution history estoppel applies to prevent the patentee from recapturing subject matter surrendered by amendment as a condition of obtaining the patent.3

    In the Festo line of cases, the federal circuit and the Supreme Court have sought to clarify when and how prosecution history estoppel may limit the use of the doctrine of equivalents in determining patent infringement. The Festo litigation first began in 1988 when Festo filed suit against Shoketsu Kinzoku Kogyo Kabushiki Co. and SMC Pneumatics, Inc. (collectively, SMC) for infringement of two patents for magnetically coupled rodless cylinders. Before the United States District Court for the District of Massachusetts, SMC's accused device was found to infringe certain claims of these patents under the doctrine of equivalents. 4

    After initially affirming the district court's judgment,5 the federal circuit reviewed the case en banc to address certain issues relating to prosecution history estoppel and the doctrine of equivalents that it felt "remained in the wake of" the Supreme Court's decision in Warner-Jenkinson.6 In this en banc decision, the federal circuit held that: (1) an amendment made for a "substantial reason related to patentability" that may give rise to an estoppel is not limited to overcoming prior art, but encompasses other reasons relating to the statutory requirements for a patent; (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; (3) no range of equivalents is available for an amended claim limitation when prosecution history estoppel applies; and (4) "unexplained" amendments are not entitled to any range of equivalents.7 The federal circuit concluded that the limitations at issue in Festo had been narrowed by amendments and that Festo had failed to establish reasons unrelated to patentability for those amendments. It also held that no range of equivalents was available for the amended claim limitations. Consequently, the federal circuit reversed the district court's judgment of infringement with respect to both patents. 8

    However, the Supreme Court rejected the federal circuit's complete bar to the use of any equivalents for situations where claim elements narrowed during patent prosecution.9 Instead, the Supreme Court reaffirmed the case-by-case analysis that it had set forth in Warner-Jenkinson and held that narrowing amendments create a presumption that the patentee surrendered any equivalents that fall within the territory between the original claim limitation and the amended claim limitation.10 The Supreme Court noted that this presumption may be overcome if the patentee can demonstrate 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.11

    Observing that the narrowing amendments at issue in Festo were made for reasons related to patentability, the Court remanded the case so that the lower courts could determine in the first instance whether Festo could demonstrate that the narrowing amendments did not surrender the particular equivalents in question.

    The Federal Circuit's Revised Analysis

    In its most recent en banc decision, the federal circuit first reiterated the portions of its prior holding that had not been disturbed by the Supreme Court: (1) a narrowing amendment made to comply with any provision of the Patent Act may invoke prosecution history estoppel, including changes made purely as to form; (2) a "voluntary" amendment may also give rise to the estoppel; and (3) in the case of an unexplained amendment, a patentee's failure to overcome the Warner-Jenkinson presumption gives rise to the new Festo "presumption of surrender" of all subject matter between the broader and the narrower language."12

    According to the federal circuit, the Warner-Jenkinson and Festo presumptions operate together as follows. The first question is whether an amendment filed in the Patent Office has narrowed the literal scope of a claim. 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 patentability.

    When the prosecution history 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. In this regard, the federal circuit held that a rebuttal of the Warner-Jenkinson presumption is restricted to the evidence contained in the prosecution history. If the patentee successfully establishes that the amendment was not for a reason related to patentability, 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 scope of the subject matter surrendered by the narrowing amendment must be addressed.

    At this point the presumption is that the patentee has surrendered all territory between the original claim limitation and the amended claim limitation. The patentee may rebut this Festo presumption of total surrender by demonstrating: 1) that the alleged equivalent would have been unforeseeable at the time of the narrowing amendment; 2) that the rationale underlying the narrowing amendment bore no more than a tangential relation to the equivalent in question (as determined solely from the prosecution history); or 3) that there was "some other reason" suggesting that the patentee could not reasonably have been expected to have described the alleged equivalent.

    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 of whether the accused element is in fact equivalent to the limitation at issue may be reached on the merits.

    Impact of the Festo Decisions

    The Festo decisions have created "new presumptions for the exception to the exception to the standard rule for infringement" that disrupt a fundamental aspect of patent practice (amending claims) that may have serious consequences on the acquisition and enforcement of patents. The Festo decisions have clearly shifted the burden to the patentee to establish the extent of equivalents that remain whenever an amendment is made to a claim. This strengthens the position of potential infringers in defending themselves where literal infringement does not exist. In this regard, the new Festo rules appear to provide greater certainty in determining the infringement of patents.13

    However, a certain amount of uncertainty still exists. For example, the determination of what constituted a "narrowing" amendment may often be difficult. When a narrowing amendment is found, determination of the aspects of a claim that were actually narrowed so as to lose equivalents may be hard to ascertain. Practical application of the "narrowing" rule is potentially further complicated in many cases in which an originally submitted claim was replaced with a new claim with different claim elements. In addition, because the Festo decisions are retrospective, many existing patents could be far less valuable than originally thought due to the unintended impact of amendments made prior to the new Festo rules.

    1 Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 2003 U.S. App. LEXIS 19867 (Fed. Cir. Sept. 26, 2003).
    2 Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002).
    3 Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 33 (1997).
    4 Specifically, the District court granted partial summary judgment that SMC¿s accused device infringed certain claims of these patents under the doctrine of equivalents, and a jury also found that SMC¿s accused device infringed other claims under the doctrine of equivalents. Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., No. 88-1814-PBS (D. Mass. Oct. 27, 1994).
    5 Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 72 F.3d 857 (Fed. Cir. 1995), vacated and remanded, 520 U.S. 1111 (1997).
    6 Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 234 F.3d 558, 563 (Fed. Cir. 2000) (en banc).
    7 Id. at 566-78.
    8 Id. at 588-91.
    9 See our prior discussion of this decision in The IP Report, Summer 2002, pp. 1-4.
    10 Festo Corp., 535 U.S. at 740.
    11 Id. at 741.
    12 Festo Corp., 2003 U.S. App. LEXIS 19867.
    13 Id., Judge Rader¿s concurring opinion at 2.