Introduction

    In the en banc decision Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., No. 95-1066 (Nov. 29, 2000), the Federal Circuit laid to rest several festering questions regarding the doctrine of equivalents.  In doing so, it greatly limited the scope and applicability of the doctrine.  This bulletin summarizes the main holdings of Festo.  The decision itself, however, is a whopper, totaling over 150 pages, including the main opinion, two concurring opinions, and four opinions concurring-in-part and dissenting-in-part.  For readers interested in the details, please click here for the full text of the decision.  Additionally, please feel free to contact me if you have any further questions regarding Festo after reading this bulletin.

The Doctrine of Equivalents

    The doctrine of equivalents is an equitable doctrine that prevents an accused infringer from avoiding infringement by changing only minor or insubstantial details of a claimed invention, while retaining the invention’s essential identity.  For example, a patent may claim two plates connected by a screw.  Under the doctrine of equivalents, an accused infringer may still be liable for patent infringement if it substitutes a rivet for the screw.  Although the claim limitation of a screw does not read literally on a rivet, a rivet may nevertheless be found to be an equivalent of a screw, ensuring the infringement of the patent.

    A general issue that has been raised by the Federal Circuit over the past decade or so is the interplay of the doctrine of equivalents with the notice aspect of patents.  The claims of a patent generally have two aims.  First, they serve to indicate the extent of the limited monopoly accorded to the patent holder.  Second, the claims serve to give notice to the public as to what is, and what is not, covered by the patent.  The doctrine of equivalents to some extent is contradictory to this latter goal.  For example, if a claim covers two plates connected by a screw, the public has notice that the claim does not cover two plates connected by another fastening mechanism, such as a rivet.  Under the doctrine, however, using a rivet may nevertheless subject the accused infringer to liability.

    Furthermore, a recognized factor that militates against application of the doctrine of equivalents is the doctrine of prosecution history estoppel.  If a patent applicant relinquishes claim coverage during prosecution, the applicant cannot later in litigation regain the coverage under the doctrine of equivalents.  For example, a claim may initially be directed to two plates connected by a fastening mechanism.  To overcome prior art cited by the examiner, the claim may be amended in prosecution to plates connected by a screw.  Prosecution history estoppel may prevent the patentee from claiming in litigation that a rivet is equivalent to a screw.  Because a rivet is arguably also a fastening mechanism, and coverage to a fastening mechanism was given up by the patentee during prosecution, the doctrine of equivalents is no longer available. 

The Questions Answered by Festo

    The Festo decision in large part decides in favor of the notice function of patent claims over the doctrine of equivalents.  Festo articulates the scope and the extent to which prosecution history estoppel is available.  In particular, the Festo decision answers the following questions:

1. For the purposes of determining whether an amendment to a claim creates prosecution history estoppel, is a substantial reason related to patentability limited to those amendments made to overcome prior art under sections 102 and 103, or does patentability mean any reason affecting the issuance of a patent?

2. 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, 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, thus invoking the presumption of prosecution history estoppel, what range of equivalents, if any, is available under the doctrine of equivalents for the claim element so amended?

Question One: What is a Substantial Reason Related to Patentability?

    The first issue decided by the Federal Circuit in Festo relates to when prosecution history estoppel applies to limit the applicability of the doctrine of equivalents.  There is a body of case law that generally states prosecution history estoppel is raised only when claims have been amended to overcome an anticipation rejection under section 102, or an obviousness rejection under section 103.  Another line of reasoning, however, posits that prosecution history estoppel is invoked any time a substantial reason related to patentability is behind the amendment of a claim.

    Festo answers this question by holding 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.  An amendment that narrows the scope of a claim for any reason related to the statutory requirements for a patent gives rise to prosecution history estoppel with respect to the amended claim element.  Claim amendments made to satisfy section 112, for example, also raise estoppel.  Section 112 requires that the patent specification describe, enable, and set forth the best mode of carrying out the invention.  The section also requires that the claims set forth the subject matter that the applicant regards as its invention, and that the claims particularly point out and define the invention.

Question Two: Do Voluntary Amendments Create Prosecution History Estoppel?

    The second question decided in Festo relates to the types of amendments that give rise to prosecution history estoppel.  Most claim amendments made during prosecution are directly in response to an examiner’s objections or rejections.  However, often claim amendments are made even where the examiner has not objected to or rejected a given claim.  The applicant, for example, may have found prior art that affects patentability of the invention.  In addition to citing the prior art to the Patent and Trademark Office, the applicant may also voluntarily amend the claims to avoid reading on the prior art.

    Festo holds that any voluntary amendment that narrows the scope of a claim for a reason related to the statutory requirements for a patent gives rise to prosecution history estoppel with respect to the amended claim element.  For example, the applicant’s claim originally may read on two plates connected by a fastening mechanism.  The applicant later finds prior art regarding a rivet to connect two plates, and therefore voluntarily narrows the claim to two plates connected by a screw.  Under Festo, prosecution history estoppel limits the application of the doctrine of equivalents in this situation.

Question Three: What Range of Equivalents Is Available When Estoppel Applies?

    The third question answered by Festo relates to how, or the extent to which, prosecution history estoppel limits the applicability of the doctrine of equivalents.  The example of the previous paragraph is illustrative in describing the two approaches that can be followed.  First, a flexible bar still gives the patentee some range of equivalents.  Therefore, because the applicant gave up claim coverage only in light of prior art that shows a rivet connecting two plates, the applicant still can resort to the doctrine of equivalents to obtain infringement on anything else equivalent to a screw other than a rivet, such as a nut and bolt.  Second, an absolute bar deprives the patentee from any range of equivalents.  Therefore, because the applicant gave up claim coverage in light of prior art showing a rivet connecting two plates, the applicant is barred from using the doctrine of equivalents to obtain infringement on anything else equivalent to a screw, even a nut and bolt.

    Festo sides with the latter approach.  When a claim amendment creates prosecution history estoppel, no range of equivalents is available for the amended claim element.  The Federal Circuit reasoned that to instead favor the flexible bar would inject uncertainty into the public notice function of claims.  The public must be able to examine a claim, and the prosecution history, to make an objective and clear determination as to the coverage that will be accorded the claim in litigation.  The flexible bar, the Federal Circuit maintained, adds an aura of uncertainty to the ability of public to do this, and therefore it opted for the absolute bar.

Question Four:  Does It Matter If No Explanation for an Amendment Is Established?

    The last question answered by the Federal Circuit in Festo relates to the scenario where no explanation is established for why a claim amendment was made.  The Supreme Court in Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), had held that prosecution history estoppel acts to limit the doctrine of equivalents in such situations.  The facts of Warner provide a good example in this regard.  The claims at issue included a limitation that a process is to be carried out at a pH from approximately 6.0 to 9.0.  The upper limit of 9.0 was added during prosecution to overcome cited prior art.  However, the addition of the lower limit of 6.0 was a mystery; there was no reason for the applicant to add this limitation during prosecution.  This is an example of a claim amendment made with no explanation.

    Festo holds that claim amendments having no established explanation do not differ in the range of equivalents their affected claim elements are accorded.  Consistent with the answer to question three, such claim amendments are not entitled to any range of equivalents.  The Federal Circuit’s reasoning here is also based on the notice function of claims.  When the public examines the language of a claim and the file history as to how that language was inserted into the claim, there should be maximum clarity to what the patentee is claiming coverage.  Allowing a flexible bar for unexplained claim amendments would add uncertainty to this process.

Analysis and Conclusion

    The Festo decision lays to rest much of the controversy of the application of the doctrine of equivalents, and the extent to which it is limited when applied.  In large part, the Federal Circuit in Festo favors the public’s ability to objectively rely on the claim language of a patent over the patentee’s ability to prevent potential infringers from trespassing its rights.  Festo implicitly holds that the notice function of patents is more important than ensuring that the patentee still is able to successfully maintain an infringement suit against clever and unscrupulous infringers.

    The Festo decision also reemphasizes the need for careful and clearly drawn patent claims submitted in the original filing of an application.  Claims that are amended during prosecution for reasons of patentability will not lend themselves to application of the doctrine of equivalents later in litigation.  It is important, therefore, that some of the claims be clearly enough drafted, and perhaps sufficiently narrow, that they will survive prosecution without amendment for reasons of patentability.  While Festo is likely not the last word on the doctrine of equivalents, it was spoken with the full force of the Federal Circuit, and therefore must be seriously heeded.