Blueprint of a gear train.

 Robert J. Yarbrough
Patent Attorney

 Patents - Inventions - Trademarks 

 The Doctrine of Equivalents

Robert J. Yarbrough

 I.   Introduction

 The doctrine of equivalents is a common law doctrine providing generally that a patent may be infringed even if the literal claims of the patent are not infringed. The most often-quoted definition is from Graver Tank, infra, and provides that a device will infringe the claims of a patent under the doctrine of equivalents if it “performs substantially the same function in substantially the same way to obtain the same result” as the claimed invention.  The doctrine of equivalents serves to expand the patent protection beyond the literal language of the claims.  The related doctrine of prosecution history estoppel provides that a patentee may not protect subject matter under the doctrine of equivalents that was surrendered during the prosecution of the patent.  A tension exists between the two doctrines and they have been the subject of extensive litigation.   Modern Supreme Court jurisprudence on the subject of the doctrine of equivalents generally dates to Graver Tank v. Linde, infra.  The Court has revisited the issue twice since Graver Tank.  In Warner-Jenkinson v. Hilton Davis, infra, the Court examined the interface between the doctrine of equivalents and the doctrine of prosecution history estoppel.  In Festo v Shoketsu Kinzoku Kogyo, infra, the Court again considered the scope of prosecution history estoppel.  Each of these cases is discussed below.

 II.  Supreme Court Cases

      A.   Graver Tank v Linde, 339 U.S. 605 (1950).

           1.   Factsimage of welding

 The technology in question was the formulation of welding flux.  The Linde patent claimed welding fluxes including ‘earth metal silicates.’  Linde’s flux actually did not conform to the literal claims of the patent and included instead over 80% magnesium silicate, which is not an “earth metal.”  Graver copied Linde’s flux, and Linde alleged patent infringement.  Since there was no literal infringement, Linde’s claim was based on the doctrine of equivalents. 

           2.   Doctrine of equivalents

 The majority held the patent to be infringed under the doctrine of equivalents.  The Court made the famous statement that:  A patentee may invoke this doctrine to proceed against the producer of a device “if it performs substantially the same function in substantially the same way to obtain the same result.”  The Court actually quoted this language from an earlier case, Sanitary Refrigerator v Winters, 280 U.S. 30.  Justice Black on dissent noted that use of magnesium silicate as a flux was old in the art and was addressed by earlier patents.  Although Linde’s research and development effort had studied magnesium silicate extensively prior to submission of the patent application, Linde did not try to claim the magnesium silicate.  Justice Black speculated that the reason was that Linde knew that it would not be able to patent compositions of magnesium silicate in light of the prior art.

           3.   Sword vs. shield

 In dicta the Court noted that the doctrine of equivalents can be used as a sword as well as a shield.  The Court said:  The wholesome realism of this doctrine is not always applied in favor of a patentee but is sometimes used against him.  Thus, where a device is so far changed in principle from a patented article that it performs the same or a similar function in a substantially different way, but nevertheless falls within the literal works of the claim, the doctrine of equivalents may be used to restrict the claim and defeat the patentee’s action for infringement.

B.   Warner-Jenkinson Company v. Hilton Davis Chemical Co., 520 U.S. 17 (1997)image of dyes

              1.   Facts

 The technology at issue in Warner-Jenkinson was the production of dyes.  Hilton Davis’ applied for a patent using an ‘ultrafiltration’ process.  In response to an examiner’s rejection based on a prior art patent that operated at a pH of greater than 9, Hilton Davis amended the claims.  The amendment restricted the claims to operation at a pH of greater than 6 but less than 9.  Hilton Davis clearly limited the claim to the higher pH limit to avoid the prior art.  There was no explanation as to why Hilton Davis included the lower pH limit.  The patent issued with the pH limitations.  Warner-Jenkinson developed a similar dye production process that operated at a pH of 5.  Hilton Davis sued, arguing infringement.  Since there was no literal infringement, Hilton Davis argued infringement under the doctrine of equivalents.

           2.   Attack on doctrine of equivalents

 Warner-Jenkinson mounted a broad-based attack on the doctrine of equivalents, arguing among other things that the doctrine as set forth in Graver Tank did not survive the 1952 Patent Act, that the doctrine violated the requirement of section 112 that the patentee specifically claim his invention, and that the doctrine violated the primacy of the Patent and Trademark Office to set the patent’s scope.  The Court rejected these arguments.   The Court also rejected Warner-Jenkinson’s argument that the doctrine of equivalents was replaced by the addition of equivalents language to section 112(6), relating to means-plus-function claims.  The Court noted that the purpose of section 112(6) was to overrule a specific case prohibiting means-plus-function claims and that the purpose of the equivalents limitation in section 112(6) was to limit means-plus-function, not to expand the scope of such claims.  In short, equivalents language in section 112(6) had nothing to do with the doctrine of equivalents.  The Court expressed concern at the broad manner in which the doctrine of equivalents had been applied in cases subsequent to Graver Tank effectively to enlarge patent claims.  The Court stated that the doctrine should be applied on an element-by-element basis rather than to the invention as a whole to protect the integrity of the claims.

           3.   Prosecution history estoppel

 The Court considered the effect of prosecution history estoppel on the doctrine of equivalents.  Prosecution history estoppel means that a patentee who surrenders subject matter during patent prosecution cannot later allege infringement of the surrendered subject matter under the doctrine of equivalents.  The doctrine prevents a patent holder from gaining subject matter in an infringement action that the patent holder could not obtain from the Patent and Trademark Office.  The Court held that the reason for an amendment during prosecution is paramount.  If the reason relates to patentability by avoiding prior art, clearly the amendment works an estoppel.  If the reason is for some other purpose, an estoppel may not be appropriate.  The amendment in question was made for an unknown purpose.  In this instance, the Court held that the burden was on the patentee to demonstrate that the amendment was not ‘related to patentability.’   The Court did not address the scope of the prosecution history bar.  The Court also did not address what would happen if an amendment was made for the reasons related to patentability but not to avoid prior art.

     C.   Festo Corp. v Shoketsu Kinzoku Kogyo, number 00-1543, decided May 28, 2002.Festo logo

          1.   Facts

 The technology in question in the two Festo patents related to magnetic conveyors.  The claims of the first patent application were initially rejected under section 112 because the exact method of operation was unclear and some claims were multiply dependent.  The applicant submitted a new application containing additional information to meet the examiner’s objection.  The claims also were amended and included new limitations relating to magnetizable materials and design of sealing rings.  The second patent, which had been issued, was amended in reexamination proceedings to include the sealing ring and magnetizable material limitations.  SMC (another name for Shoketsu Kinzoku Kogyo) began marketing a similar device, but with a different seal arrangement and made from non-magnetizable materials.  Festo alleged infringement based on the doctrine of equivalents.  SMC defended on the basis of prosecution history estoppel.    

           2.   Litigation history

 The district court held that the purpose of Festo’s amendment was not to avoid prior art and therefore prosecution history estoppel did not arise.  The Federal Circuit affirmed.  In the meantime, the Supreme Court decided Warner-Jenkinson v Hilton Davis.  The Supreme Court accepted certiorari and summarily remanded for further consideration.   On remand, the Federal Circuit decided (1) that any narrowing of claims to obtain a patent gives rise to prosecution history estoppel, and (2) prosecution estoppel bars every equivalent to the amended claim element.  The bar imposed by the Federal Circuit is referred to as a ‘complete bar’ as opposed to a ‘flexible bar.’  The Federal Circuit expressly overruled inconsistent precedent, holding that the doctrine of equivalents in general and the flexible bar in particular had proven to be unworkable.

           3.   The decision of the Supreme Court

               a.   Doctrine of Equivalents
 The Supreme Court restated its support for the doctrine of equivalents, even when the result is a loss of certainty and judicial economy.  The Court described the purpose of the doctrine as follows:  The doctrine of equivalents is premised on language’s inability to capture the essence of innovation, but a prior application describing the precise element at issue undercuts that premise.
               b.   Amendments creating prosecution history estoppel
 The Court first considered whether an amendment made to satisfy a rejection under the section 112 statutory requirements would give rise to an estoppel.  The Court concluded that any amendment that narrows a claim gives rise to prosecution history estoppel.  The Court further concluded that the reason for the amendment does not control.  The Court said:

Estoppel arises when an amendment is made to secure the patent and the amendment narrows the patent’s scope. … A patentee who narrow a claim as a condition for obtaining a patent disavows his claim to the broader subject matter, whether the amendment was made to avoid the prior art or to comply with section 112.

                c.   Equivalents subject to the bar   
 Although the opinion is somewhat vague, the Court apparently determined that the prosecution history estoppel bar applies only to subject matter that would have been included within the unamended claims but is not included in the claims as amended.  For example, the following discussion relates to estoppel when no reason for an amendment is established:

 …[Warner-Jenkinson provides] that when 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. (Emphasis supplied).

 Apparently, the doctrine of equivalents still applies freely to equivalents outside of the scope of the original, unamended claims.  This is a significant departure from the rule enunciated by the Federal Circuit.
               d.   Effect of the bar
 The Court examined the scope of a prosecution history estoppel bar; namely, whether the bar should be complete, as determined by the Federal Circuit, or should be flexible.  The Court came down on the side of flexibility, sort of.  The Court stated its policy reasons as follows:  There is no reason why a narrowing amendment should be deemed to relinquish equivalents unforeseeable at the time of the amendment and beyond a fair interpretation of what was surrendered.  Nor is there any call to foreclose claims of equivalence for aspects of the invention that have only a peripheral relation to the reason for amendment was submitted.  The Court gave some examples where the bar would be flexible:

There are some cases, however, where the amendment cannot reasonably be viewed as surrendering a particular equivalent.  The equivalent may have been unforeseeable at the time of the application; the rationale underlying the amendment may bear no more than a tangential relation to the equivalents in question; or there may be some other reason suggesting that the patentee could not reasonably be expected to have described the insubstantial substitute in question.  In those cases the patentee can overcome the presumption that prosecution history estoppel bars a finding of equivalence.   

              e.   Burden on the patentee
 The Court placed the burden on the patentee to prove that the prosecution history estoppel bar should not apply to a particular equivalent.  Said the Court:

[W]e hold here that the patentee should bear the burden of showing that the amendment does not surrender the particular equivalent in question.

 The Court gave guidance on how the patentee could meet its burden:

… [T]he patentee still might rebut the presumption that estoppel bars a claim of equivalence.  The patentee must show 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.

 The Court remanded to give Festo a chance to show that it did not surrender the SMC equivalents.

III. Conclusions

     1.   In the absence of prosecution history estoppel, a patent provides protection broader than the literal language of the claim.  The protection extends to accused devices that perform substantially the same function in substantially the same way to obtain the same result as the claims of the patent.      2.   If the patentee narrows the claims during prosecution for any reason, prosecution history estoppel applies and the patentee waives the difference between the subject matter of the original claims and the amended claims.  The patentee does not waive other equivalents, such as equivalents not addressed by the amendment.      3.   The presumption of a waiver is not absolute and the patentee may be able to overcome that presumption.