The
Doctrine of Equivalents
Robert J. Yarbrough
© 2002
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. Facts
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)
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.
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.
