The degree to which prosecution history estoppel limits the doctrine of equivalents has long been the subject of much debate among patent owners, competitors, and the courts. In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co.,1 the Supreme Court attempted to provide guidance on the issue by establishing that whenever patent claims are narrowed by amendment, a rebuttable presumption arises that prosecution history estoppel bars all equivalents.2 However, the Court's decision may have done more harm than good by introducing a foreseeability element into the requirements for rebutting the presumption.
The state of the law prior to Festo was unclear at best. In 1997, the Supreme Court held that prosecution history estoppel was a flexible, not an absolute, bar to the doctrine of equivalents in patent infringement cases, meaning that some, but not all, claims of equivalence would be barred.3 In 2000, the Federal Circuit departed from the flexible-bar rule by holding that whenever a patentee amends claims in order to obtain a patent, prosecution history estoppel acts as an absolute bar to the doctrine of equivalents with respect to the amended elements.4 The Federal Circuit justified its harsh, absolute-bar rule on the grounds that the flexible-bar approach had proven "unworkable" and that an absolute bar would IMAGE FORMULA3
provide desired certainty in determining the scope of an amended patent claim.5
The Federal Circuit's decision was the source of great concern to thousands of patentees because it significantly limited the range of subject matter against which a patentee could successfully assert a claim of infringement by equivalence.6 Patent claims narrowed by amendment during patent prosecution-and many claims are-- would be limited to their literal language for all amended elements, thereby depriving patentees of protection against competitors' devices falling just outside the literal language. Patentees who amended their claims with a flexible-bar rule in mind were understandably concerned that the Federal Circuit's absolute bar devalued their already-issued patents by effectively granting a much narrower monopoly.
Concerned patent holders were relieved when, on May 28, 2002, the Supreme Court vacated the Federal Circuit's decision and reinstituted a flexible-bar rule.7 In re-instituting a flexible-bar rule, the Supreme Court held that a presumption exists that prosecution history estoppel bars all equivalents but that the patent owner may rebut the presumption under certain circumstances.8 The difference, therefore, between the Supreme Court's flexible bar and the Federal Circuit's absolute bar lies in the fact that the presumption is rebuttable. The problem with the Supreme Court's decision is that it sets forth contradictory standards for how rebuttal is to be accomplished and it creates incentives that undercut the goals of the patent system.
This Note will discuss the tension between the doctrine of equivalents and prosecution history estoppel and how the Supreme Court attempted to resolve that tension in its Festo decision. Part II will briefly explain several basic patent law principles and outline the state of the law in 1997 as set forth in Warner-Jenkinson Co. v. Hilton Davis Chemical Co.,9 against which the Federal Circuit's IMAGE FORMULA5
decision and its subsequent vacation by the Supreme Court were set. Part III will follow with a description of the facts of the Festo case and a brief synopsis of the holdings of the Federal Circuit and the Supreme Court. Part IV will analyze the Supreme Court's Festo decision vacating the Federal Circuit and assert that while the Court correctly reaffirmed estoppel as a flexible, not an absolute, bar to the doctrine of equivalents, the Court undercut some of the most basic policies of the patent system by introducing foreseeability as a component of the flexible bar. …