17

Interpretation of Functional Claimsin the United States

Researcher：Takashi Ohno(*)

The way in which a patent claim should be interpreted for determining the scope of protection of a patentright is an important subject. Functional claims, which are patent claims described using functional
expressions, are convenient and are frequently used for inventions that are characterized by their functions orinventions in technical fields where there are no established terms to express the means for performing thefunctions. On the other hand, it has been indicated that functional claims make the scope of protection
ambiguous and excessively broad since they literally cover all means for performing the function. In the UnitedStates, 35 USC §112, ¶6 stipulates that a claim can be described by a combination of functions, but that thescope of protection of such a claim should be narrowly interpreted. Thus, the question of how functional claims
should be interpreted has been examined in many court decisions.
In this report, recent court decisions involving interpretation of functional claims, in particular, their scopeof protection, were analyzed based on the historical background of interpretation of functional claims in the
United States, and a brief comparative study was conducted with the situation of protection in Japan.

Ⅰ Introduction
Patent protection for an invention can only besought by stating the concrete content of theinvention in a specification and describing thecontent to be protected in the form of claims.
Although inventors try to draft broad claims to seek
a broad scope of protection, protection exceeding
the actual scope of the invention would discourage
third persons from developing new technology, andwould not benefit the whole society. On the other
hand, if the methods for expressing claims were too
limited and the inventor could only enjoy a narrow
scope of protection, it would not be possible torestrict imitations by trivial alterations. The issueof the treatment of functional claims is essentially aquestion of how to achieve balance between thefreedom in describing claims and the desirable
protection.
A functional claim is a patent claim of which atleast one part is described by a means for
performing a function. For example, by describing“a means for tightening” of a constituent element“screw,” one would not only be able to express the“screw” itself in the claim language, but the wholemeans of tightening.
Since such a patent claim can directly express
the function to be performed by a constituent
element in the claim, it is useful for claim drafters
to draft a broad claim covering the generic concept
for inventions characterized by functions, and forpatents in technical fields where words forexpressing the means for performing certain
functions have yet to be established. At the sametime, however, it has the problem of making thescope of protection too ambiguous and broad inlight of the disclosed invention, because, literally, it

covers all means for performing the function.
35 USC §112, ¶6(*1) allows inventors to
describe an element in a claim for a combination asa means for performing a specified function without
describing the structure, material, or action
involved, i.e. as a functional claim, and the scope ofprotection of such a functional claim is limited tothe embodiments described in the specification and“equivalents” thereof (hereafter “statutory
equivalents”).
However, the statutory law is insufficient forclearly determining what kinds of descriptions
should be judged as a functional claim and subject
to this provision, and how the scope of protection
would differ based on the statutory equivalents,
compared to those based on the doctrine ofequivalents. Thus, court decisions related tointerpretation of functional claims are drawing
much attention. While more and more theories
have come to limit application of the doctrine ofequivalents, as typified by prosecution history
estoppel, there is a view that the filing of patentapplications using the functional claims will
increase in the future with the aim of at leastenjoying protection of statutory equivalents.
In this report, the trend of interpretation offunctional claims in the United States, particularly
the application of the doctrine of equivalents tofunctional claims, was analyzed based on theseviewpoints.

(*) Assistant Manager, ＩＰ Dept., Kawasaki Heavy Industries, Ltd.
(*1) 35 U.S.C. §112, ¶6.

IIP Bulletin 2003

● 134 ●Ⅱ Basic Interpretation of Functional
Claims1

Background of Establishment of 35 USC§112, ¶6

The treatment of functional claims in the
United States has long been subject to debate withrespect to the balance between disclosure andprotection.
The types of claims that were addressed by
the U.S. Supreme Court in its initial period, were
those solely composed of a means for performing asingle function. The Supreme Court judged such aclaim to be invalid, stating that the patentee wasclaiming beyond his actual invention. Furthermore,in the Halliburton case(*2) in 1946, the Supreme
Court, regarding the novelty of a claim consisting ofa combined means for performing functions,declared that such a claim was invalid due to being
too broad, ambiguous, and contained an underlying
threat of going beyond its scope of invention.
However, practitioners strongly opposed thepractice of immediately invalidating functional
claims, which had been prevailing in the actual
patent affairs, and in 1952, the U.S. Congress added§112, ¶6 in response to the Halliburton casedecision in order to ensure convenience in practice,by allowing claims consisting of combined meansfor performing functions. At the same time, it
stipulated that the scope of protection should be
limited to the embodiments and equivalents thereof,so as to legislatively remove the grounds forinvalidation of being too broad, ambiguous, andcontaining an underlying threat of going beyond its
scope of invention.
2

Application of §112, ¶6 in Infringement
Lawsuits(1) Confusion over interpretation of §112, ¶6
Although the principles of interpretation of an
ordinary claim are basically applied to interpretationof a functional claim, its scope of protection isalready stipulated by statutory law, and this scope
covers the embodiments and “equivalents thereof”(statutory equivalents). Therefore, this provision
has confused the determination in practice as towhether the scope of protection defined in §112, ¶6
covered the embodiments described in thespecification and their statutory equivalents, as wellas their equivalents based on the doctrine ofequivalents (i.e., equivalents of statutory equivalents),
or whether it was almost limited to theembodiments described in the specification.

Since the 1952 amendment of the Patent Act,
courts had not indicated an interpretation beyond“the embodiments described in the specificationand equivalents thereof” and adopted a literal,
relatively broad interpretation regarding this issue.
However, the United States Court of Appeal for theFederal Circuit (hereafter “the CAFC”), which wasestablished in 1982 for the purpose of making
determination of law in appellate instances ofpatent infringement lawsuits consistent, seriously
addressed this issue.
In the DMI case decision(*3) in 1985, the CAFC
denied limited interpretation, stating that tointerpret “means plus function” limitations aslimited to a particular means defined in thespecification would be to nullify the provision
requiring that the limitation shall be construed tocover the structure described in the specificationand equivalents thereof. Based on this, the CAFC
declared that, although §112, ¶6 required somedisclosure of the enabling means for accomplishing
the function as embodiments in the specification,
there was no requirement for every possible means
to be disclosed, so the scope of protection was not
limited to the disclosed embodiments alone, andemphasized the expansion of the scope ofprotection from mere embodiments to also coverstatutory equivalents.
The Texas Instruments court decision(*4) in1986 interpreted functional claims by an extremely
peculiar argument; it is perhaps the decision which
best illustrates the CAFC’s anguish. The patent inquestion related to a miniature electronic calculator,
wherein each constituent element in the claims wasfunctionally described. In determining infringement,
the CAFC first judged that the claimed functions
were all performed in the respective elements of
the accused product, and that the accused productwas a statutory equivalent to the corresponding
structure described in the specification. Despite
literary infringement being generally found basedon this judgment, the CAFC went further tocompare the entirety of the invention to theentirety of the accused product, and denied bothliterary infringement and infringement based on thedoctrine of equivalents, on the basis that theconstituent elements of the accused product were alater-developed technology, which realized a far
smaller miniature electronic calculator than thedisclosed embodiments of the originally patented
invention. Although this decision has been
criticized by some people for not clarifying therelationship between §112, ¶6 and the reverse
doctrine of equivalents, it certainly was a case that
affected the later development of interpretation(*2) 329 U.S. 1 (1946).
(*3) 755 F.2d 1570, 225 U.S.P.Q. 236 (Fed. Cir. 1985).
(*4) 805 F.2d 1558, 231 U.S.P.Q. 833 (Fed. Cir. 1986).

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methods.
In the Valmont case decision(*5) the CAFC
stated that §112, ¶6, while allowing claim
description by a combination of functional elements
in its first part, set a limitation to that scope ofprotection in the latter part, which was a limitation
to the corresponding structure, material, or acts
described in the specification and equivalents
thereof, wherefore it operated more like thereverse doctrine of equivalents, rather than thedoctrine of equivalents because it restricted thecoverage of literal claim language.
(2) Basic principles for interpretation offunctional claims
The basic principles for interpretation offunctional claims, which were established as aresult of confusion, can be summarized as follows.
(i) Identification of the structure corresponding to
the function
The interpretation is made in two stages. The
first stage is to identify the claimed function.
Interpretation of the claimed function is based on
the principles for interpretation of ordinary claims,
and it is inappropriate to interpret the scope ofclaim narrower or broader than the literal claim
language.
After distinguishing the function, determination
is made as to composition of the structure disclosed
in the specification corresponding to the claimed
function. For sufficient correspondence, thestructure needs to perform the claimed function,and the specification must clearly associate thestructure and the enabling of the function. This
criterion must be determined from the viewpoint ofa person skilled in the art in that technical field. A
patent claim is effective not only when two
embodiments are disclosing separate corresponding
structures, but also when a single embodiment isdisclosing the corresponding structure.
On the other hand, if it becomes clear thatnone of the embodiments disclose the structure
corresponding to the claimed function, the claim
will be invalid for failing to satisfy the definitenessrequirement in §112, ¶2(*6). However, there is slight
confusion in recent court decisions(*7) as to theextent to which the corresponding structure must
be described and whether everything including thecommon knowledge of a person skilled in the art
must be described. While there is a possibility of
being able to enjoy a remedy to the effect that aperson skilled in the art can understand thecorresponding structure even if it were notdescribed, there is also an opinion that such remedy
should not be extended based on the purport of§112, ¶6. Therefore, when one seeks to receive

application of §112, ¶ 6, he/she needs to sufficiently
describe the corresponding structure for
performing the function described in the claim. In
addition, since the scope of the corresponding
structure for performing the function becomessubject to dispute(*8), it is also necessary to
sufficiently describe the corresponding relationshipin the specification so as to prevent it from being
construed with unnecessary limitation.
(ii) Scope of protection of functional claims(A) Literal infringement
After identifying the function and thecorresponding structure, examination is made as toliteral infringement. Examination on literal
infringement of a functional claim includes twodetermination items. The first is determination ofwhether or not the accused product performs thesame function as the claimed function. The second
is determination of whether or not the accused
product has the same structure as or a statutory
equivalent to the structure corresponding to thefunctional elements described in the specification.
The “statutory equivalent” here means theequivalent within the coverage of literal claim
language, as is explained as the reverse doctrine ofequivalents in the Valmont case decision, and isdifferent from the doctrine of equivalents, whichattempts to cover minute differences that do notcorrespond to claim language.
By reading the language of a functional claim
as is, everything would be covered as long as it
performs the same function. Nevertheless, the enbanc decision in the Pennwalt case(*9) in 1987 stated,while citing an explanation by Judge Rich who was
one of the drafters of §112, ¶ 6, that the literal
scope of a functional claim would be construed as
the structure corresponding to the function
described in the specification and equivalents
thereof. Based on this, the CAFC judged that literal
infringement of a functional claim must be
determined by comparing the accused product andthe structure described in the specification to judge
not only the identity of the function performed by
the structure, but also whether the structure was
equivalent.
Thus, literal infringement of a functional claim
is determined by comparing the accused productand the structure corresponding to the function
described in the specification, based on the premiseof identity of the function, and by judging whether
or not the two are identical or equivalent.
As the determination standards for “statutory
equivalents,” the “tripartite test” and the“interchangeability test” may be used. Although thetwo tests have different purposes and origins, they(*5) 983 F.2d 1039, 25 U.S.P.Q. 2d 1451 (Fed. Cir. 1993).
(*6) 35 U.S.C. §112, ¶2.
(*7) S3 Inc. v. Nvidia Co., 259 F.3d 1364, 59 U.S.P.Q.2d 1745 (Fed. Cir. 2001).
(*8) Odetics, Inc. v. Storage Tech. Corp., 185 F.3d 1259, 51 U.S.P.Q.2d 1225 (Fed. Cir. 1999).
(*9) 833 F.2d 931, 4 U.S.P.Q.2d 1737 (Fed. Cir. 1987) (en banc).
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● 136 ●

are closely related in that they both make thedetermination based on the insubstantial difference.
Nevertheless, since the accused product is notcompared with the claim itself, but the structure
corresponding to the function described in thespecification, there is confusion as to how strict thecomparison should be.
Such state of confusion was most clearly
illustrated by the IMS case decision and the Kemcocase decision rendered in 2000.
In the IMS case(*10), the plaintiff, IMS, owned apatent relating to a control system fornumerically-controlled machine tools that enabledinteractive programming of the processes, and theclaim included an “interface means” fortransferring data from an external storage medium
into a memory. In the embodiment disclosed in thespecification, a cassette tape device was disclosed
as the structure corresponding to the “interface
means,” while the product of the defendant, Haas,
was a floppy disk drive. The district court decision
denied literal infringement on the basis that the twowere not equivalent structures, among otherreasons. In the appellate instance, Judge Plager
explained that a “statutory equivalent” only
required the two to have equivalent structures, anddid not require them to be structural equivalents.
He stated that the determination of equivalentsshould be made from the context of the claimed
invention. The CAFC remanded this case to the
district court for further proceedings on thefollowing bases: “interface means” was merely away of storing created data; its physicalcharacteristics were not important to the invention;and the plaintiff had supplied evidence on theinterchangeability of the two apparatuses.
This decision explored a new aspect indetermination of “statutory equivalents,” in thatthe scope of equivalents could be flexibly
determined according to the importance of theelement.
The Kemco case decision(*11), in contrast, clearly
indicated the need for component-by-component
structural comparison. The plaintiff, Kemco, owned
a patent relating to an envelope, which prevented itfrom being illicitly opened. With conventional
envelope technology, the adhesive can be melted byheat, so their enclosed contents could be removed
without leaving a trace of being opened. This patent
was characterized by having two kinds of sealingmeans in order to solve this problem: the first being
an ordinary sealing means merely intended forclosing the envelope, and the second being asealing means that easily reacted to and wasdamaged by heat. In addition, the claims included afunctional element, “closing means.” Thedefendant’s product also had two kinds of sealingmeans for preventing it from being illicitly opened.
However, these two differed in that, while the twokinds of sealing means were attached to a fold-overflap in the embodiment of the plaintiff’s invention,
the defendant’s product was comprised of a dual-lip
structure that covered the inside of the envelope
opening as well as the whole outside of theenvelope opening. In analyzing literal infringement,
Judge Lourie compared the structural features ofthe defendant’s product and the embodiment, andfinding that, although the two coincided in having
the same function of closing the envelope, thedifference in their structure resulted in a difference
between the structures for attaching the adhesive,
he declared the way and the result for performing
the function to be substantially different, and denied
literal infringement. He also stated that thedoctrine of equivalents was inapplicable because it
was already clear that the way and the result weredifferent, and supported the district court decisionof non-infringement.
In this decision, no examination was made as
to the importance of the functional elements, which
was indicated in the IMS decision, but only
structural comparison was conducted. If thestandard in the IMS decision was applied to thiscase, the important part of the invention would be
to use two kinds of sealing means, and not thestructure itself for closing the envelope, so areverse conclusion could have been derived.
In this manner, courts have been making effort
to clarify the determination standards by indicatingthat the tests for the doctrine of equivalents can beused to determine “statutory equivalents,” butcourt decisions still remain unstable.
(B) Doctrine of equivalents
Even if literal infringement could not be found,infringement under the doctrine of equivalents
could be established if the difference between theclaimed invention and the accused product orprocess were insubstantial. Functional claims
already encompass the “statutory equivalents”
under statutory law. Therefore, applicability of thedoctrine of equivalents to functional claims has
been questioned in terms of overprotection andindefiniteness of the scope, and many people had
been negative about such application.
Nevertheless, CAFC decisions in recent years
have clarified the difference between the two, andhave judged that functional claims could also beprotected by the doctrine of equivalents.
Application of the doctrine of equivalents tofunctional claims will be discussed in detail in
Chapter III.
(iii) Scope of protection of functional claims andprosecution history
Prosecution history is taken into account to(*10) 206 F.3d 1422, 54 U.S.P.Q.2d 1129 (Fed. Cir. 2000).
(*11) 208 F.3d 1352, 54 U.S.P.Q.2d 1308 (Fed. Cir. 2000).
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interpret the literal scope, that is, to determine theextent of “statutory equivalents” in interpretationof a functional claim, while it also sometimes
functions to limit application of the doctrine ofequivalents. In addition, since a functional claim
covers “statutory equivalents” under its literal
scope, when a functional claim is amended into an
ordinary claim, a mere amendment to replace themeans-plus-function limitation with the structure
corresponding to the functional element will be
judged as a narrowing amendment.
(iv) Who should determine the scope of afunctional claim
While the literal scope of a functional claim
includes the corresponding embodiments and theequivalents thereof, there is a controversy overwhether determination on these “statutory equivalents”
should be considered as a question of law, since it is
only a question of literal interpretation of the claim,
or it should be considered as a question of fact thatshould be judged by a jury, since suchdetermination inevitably assumes identification of
the accused article, to determine whether thearticle is directly covered by the literal scope. With
regard to this issue, the CAFC judged in the
Odetics case decision(*12) that whether an accused
product or process performed the same function by
the same structure, material, or acts, or equivalents
thereof, was a question of fact.
3

Application of
Examination

§112,

¶6

to

Patent

The courts have treated the scope ofprotection for a functional claim to be different fromthat for an ordinary claim, but the United States
Patent and Trademark Office (hereafter the“USPTO”) has considered §112, ¶6 to be a provision
for infringement litigation, and has examinedfunctional claims by a broad interpretation similar
to ordinary claims in the patenting procedure.
In the In re Donaldson(*13) case, the CAFC
stated that the “broadest reasonable interpretation”
of a functional claim was merely the scope to which§112, ¶6 was applied, and strongly encouraged the
USPTO to apply §112, ¶6 in the patent examination
phase. In response, the USPTO revised its Manualof Patent Examining Procedure (MPEP) to apply§112, ¶6 also in examination(*14).
Accordingly, identification of the gist of theinvention becomes an issue in patent examination.
If the examiner finds that a prior art element (A)performs the function specified in the claim, that(B) is not excluded by any explicit definition
provided in the specification for an equivalent, andthat (C) is an equivalent of the means- (or step-)plus-function limitation, the examiner should
provide an explanation and rationale in the Officeaction as to why the prior art element is anequivalent(*15). In the explanation as to why theprior art element is an equivalent, if the examiner
indicates a prima facie case of equivalence based on
at least one of the tripartite test, interchangeability
test, insubstantial difference, or structural equivalence,
based on a prior CAFC decision, the burden of proof
will be shifted to the applicant, and the patent will
not be issued unless the applicant proves that theprior art element is not an equivalent. Even if theapplicant proves that the prior art element is not an
equivalent, the examiner still has to examine theunobviousness analysis under §103(*16).
The applicant may prove that the prior art
element is not an equivalent by reasons including
teachings in the specification that specific prior art
is not equivalent, teachings in the prior art
reference itself that may tend to show
nonequivalence, or affidavit evidence of facts
tending to show nonequivalence(*17).
4

Once a claim is judged to be a functional claim,
the special treatment under §112, ¶6 becomesapplicable both in infringement litigation and patentexamination, so the standard for determining whatkind of description is a functional claim becomes aquestion.
Indeed, this point has been debated in many
court decisions, and a standard of rebuttablepresumption based on a special description form
was established.
The MPEP summarizes the determination
standards for invoking §112, ¶6 as follows, by citing
many CAFC decisions(*18):(a) the claim limitations must use the phrase“means for” or “step for”;(b) the “means for” or “step for” must be modified
by functional language; and(c) the phrase “means for” or “step for” must not
be modified by sufficient structure, material oracts for achieving the specified function.
However, the omission of the phrase “meansfor” or “step for” does not preclude application of§112, ¶6.

(*12) 185 F.3d 1259, 51 U.S.P.Q.2d 1225 (Fed. Cir. 1999).
(*13) 16 F.3d 1189, 29 U.S.P.Q.2d 1845 (Fed. Cir. 1994).
(*14) MPEP §2181-186 (2001).
(*15) MPEP §2183.
(*16) Supra note.
(*17) MPEP §2184.
(*18) MPEP §2181.

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Standards for Invoking §112, ¶6● 138 ●

Ⅲ Application of the Doctrine ofEquivalents to Functional Claims
The applicability of the doctrine of equivalents
to functional claims has been questioned in terms ofoverprotection and indefiniteness of the scope, andhas been subject to considerable debate, but recent
court decisions have indicated two determination
standards.

embrace technology developed after the issuance ofthe patent, while such a technology could be also
included under the doctrine of equivalents. He also
added, while the function must be identical in thecase of an equivalent under §112, ¶6 that premises
literal infringement, the function needs only to be
substantially the same in the case of the doctrine ofequivalents.
2

1

Difference in the Timing of Analysis

Chiuminatta case(*19)
In this case, the CAFC denied literal
infringement, stating that the accused product was
not a statutory equivalent under §112, ¶6, and theapplicability of the doctrine of equivalents became
the point of discussion. In the decision, Judge
Lourie, while acknowledging that the statutory
equivalents under §112, ¶6 and the doctrine ofequivalents had different purposes and origins,declared that they were similar, in that theyprotected the substance of a patentee’s right toexclude, by preventing mere colorable differences
or slight improvements from escaping infringement
by applying similar analyses of insubstantiality ofthe differences. He therefore judged that “a findingof a lack of literal infringement for lack ofequivalent structure under a means-plus-function
limitation may preclude a finding of equivalence
under the doctrine of equivalents.”
Nevertheless, he explained the role of thedoctrine of equivalents that, since the doctrine ofequivalents could protect against a variant
technology at the time of infringement while literal
infringement could not protect against after-arisingtechnology, even if such an after-arising variant wasdenied of being a §112, ¶6 equivalent, this analysis
should not foreclose it from being an equivalent
under the doctrine of equivalents.
(ii) Al-Site case(*20)
As the accused technology in this case was not
an after-arising technology either and no courts
have applied the doctrine of equivalents based on
this reasoning, the details of this case shall beomitted. In the course of the determination,
however, Judge Rader cited some court decisions
that analyzed the difference between an equivalent
under the doctrine of equivalents and an equivalent
under §112, ¶6, and analyzed that one importantdifference between §112, ¶6 and the doctrine ofequivalents was the timing of the separate analyses
for an “insubstantial change.” He stated that anequivalent under §112, ¶6 must have existed at thetime of the issuance of the patent, and it cannot(i)When the Function is Not the Same, But
Substantially the SameThe two court decisions clearly summed up
the application of the doctrine of equivalents tofunctional claims based on the difference in thetiming of analysis for application, but theprerequisite, “when having the same function,” hasan extremely important meaning. Specifically, it is aquestion of whether the doctrine of equivalents
would be applicable when the function was not “thesame” but was “substantially the same.” Thispossibility was not denied in obiter dictum in the
Al-Site decision, but about four months later, in the
WMS Gaming case in 1999, the CAFC actually
made judgment on this issue for the first time.
(1) WMS Gaming case(*21)
The plaintiff owned a patent relating to a slot
machine which increased the gambling aspect by
decreasing the odds of winning. The defendant,
WMS Gaming, was selling a slot machine which
also decreased the odds of winning, but while thepatent had virtually increased the reel stop
positions, the defendant’s product first calculated
the payoff and controlled the reel to stop at theposition that represented that payoff.
In the decision, Judge Schall affirmed that thedefendant’s product was a statutory equivalent, butdenied literal infringement for not performing afunction identical to that described in the claim.
Nevertheless, in the determination of thedoctrine of equivalents, he judged that infringement
was found under the doctrine of equivalents basedon the district court’s decision that the two
products were equivalents, since the function was
substantially the same though not identical.
(2) Interactive Pictures case(*22)
The plaintiff, Interactive Pictures, owned apatent relating to a device for image viewing, whichdisplayed a specific part of circular image data takenfrom a fish-eye lens camera by correcting it into anormal image. The patent claim in issue included
an “image transform processor means for...” among
other multiple functional elements, and the patent
was characterized by the fact that the system
converted the circular image by electronic(*19) 145 F.3d 1303, 46 U.S.P.Q.2d 1752 (Fed. Cir. 1998).
(*20) 174 F.3d 1308, 50 U.S.P.Q.2d 1161 (Fed. Cir. 1999).
(*21) 184 F.3d 1339, 51 U.S.P.Q.2d 1385 (Fed. Cir. 1999).
(*22) 274 F.3d 1371, 61 U.S.P.Q.2d 1152 (Fed. Cir. 2001).
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calculation, without mechanically moving thecamera, preferably at real time rates. The defendant,
Infinite, manufactured and sold a software package
composed of image-making software that created a
360 degree panorama image by seaming images
taken by a fish-eye lens camera or similar device,
and a viewer that displayed a desired portion of a
panorama image in an equirectangular format as anormal image.
In the appeal from the district court’s decisionthat found infringement under the doctrine ofequivalents, the defendant cited the Chiuminatta
decision and claimed that the doctrine ofequivalents was inapplicable since the “imagetransform processor means” limitation was not
literally present in the defendant’s product. In
response, Judge Lourie summarized that theChiuminatta decision and the WMS Gaming decision
had different preconditions as follows: “In Chiuminatta,
we held that a finding that a component of an
accused product is not a structure ‘equivalent’ tothe corresponding structure of a means-plus-function
limitation for purposes of literal infringement
analysis, precludes a finding that the samestructure is equivalent for purposes of the doctrineof equivalents, unless the component constitutes
technology arising after the issuance of the patent.
However, when a finding of noninfringement under
35 U.S.C. §112, ¶6, is premised on an absence ofidentical function, then infringement under thedoctrine of equivalents is not thereby automatically
precluded.” Based on this, the CAFC held that, in
this case, as in WMS Gaming, the absence of literal
infringement was due to a lack of identical functionof the claimed means, not a lack of equivalent
structure, and it did not preclude application of thedoctrine of equivalents. In conclusion, the CAFC
found no error in the district court’s decision,
which allowed application of the doctrine ofequivalents, and affirmed the decision.
3

Summary

Although there had been negative views on
the applicability of the doctrine of equivalents tofunctional claims because the word “equivalents
thereof” is already stipulated in statutory law
regarding the scope of protection for functional
claims, the above two categories of application of
the doctrine of equivalents have been clarified.
With regard to the former, when an accused
product is denied as being a statutory equivalent interms of structure, even though it performs thesame function as the claimed functional element,
the determination will be made based on a similar
standard – insubstantial difference – and thedoctrine of equivalents will be inapplicable.
However, the literal scope of protection isdetermined at the time of the patent issuance,
which under the doctrine of equivalents is

IIP Bulletin 2003

determined at the time of infringement, so if theaccused product is an after-arising technology, it
could become subject to the doctrine of equivalents.
On the other hand, in the case of the latter thedoctrine of equivalents will be applicable if thefunction is not the same, but substantially the same,and the difference between the accused productand the patented invention is insubstantial.
Consequently, the scope of protection takes aseemingly odd structure in which the possibility of
infringement arises again by choosing a structure
farther away from the claim language.

Ⅳ Considerations on the Applicationof the Doctrine of Equivalents toFunctional Claims
The scope of protection of a functional claim in
the United States covers the structure
corresponding to the function described in thespecification and equivalents thereof, and additional
protection under the doctrine of equivalents may
also be enjoyed. In determining whether or not anaccused product is covered by the literal scope ofthe claim, i.e., whether or not it is judged to be an
equivalent of the structure corresponding to thefunction, determination standards that are almost
identical to the doctrine of equivalents are being
used as a result of various debates, although there
was a discussion that the concept of the statutory
equivalents and that of the doctrine of equivalents
had different purposes and origins. Specifically,
whether or not an accused product and thestructure corresponding to the function are
insubstantially different is judged by whether or not
the way and the result are the same or a person
skilled in the art could have known theinterchangeability, on the basis that the function is
the same. If the accused product having the samefunction is judged not to be a statutory equivalent
as a result of this analysis, it will not be an
equivalent under the doctrine of equivalents either,unless it is an after-arising technology. Since thetripartite test does not require the function to be
the same, but only substantially the same, thedoctrine of equivalents may also be applicable when
the function is not the same, but substantially thesame.
Is such a scope of protection appropriate as thescope of protection of a functional claim? In
particular, when applying the doctrine ofequivalents based on substantial identity of thefunction, the possibility for application of thedoctrine arises again by deviating from the literal
scope, on the condition that the function is not
identical, which appears to take an abnormal
structure. Can this be considered as appropriate
protection?
The doctrine of equivalents is originally a● 140 ●

theory that tries to expand the scope of protectionof a patent right to an area that does not necessarily
coincide with the literal scope, in order to prevent
unlawful imitators from escaping infringement bymaking substantially unimportant changes. On theother hand, §112, ¶6 is a theory of limitation thattries not to expand the scope of protection beyond
what has actually been assumed by the inventor incompensation for allowing the inventor some
freedom in expression by allowing claim description
by a combination of functions performing theconstituent elements of the invention. Since thetwo theories thus have different purposes andorigins, it may not always be appropriate to use adetermination
methodofapplying
thescope-expanding theory of the doctrine ofequivalents to the determination of statutory
equivalents under §112, ¶6. Indeed, an older court
decision has indicated a view that the statutory
equivalents under §112, ¶6 already include theequivalents under the doctrine of equivalents.
Nevertheless, prior to the establishment ofsuch a determination method, there was only amethod for determining statutory equivalents
under §112, ¶6, and since §112, ¶6 was not properly
functioning as a limiting theory, the literal broad
scope of protection had been allowed as a result.
Therefore, it is possible to say that the limiting
theory of §112, ¶6 actually started to operate only
after the CAFC accumulated case law on themethod for determining statutory equivalents under§112, ¶6, and indicated that such determination could
be approached by applying the doctrine of equivalents.
In that sense, the approach using the doctrine ofequivalents could be highly valued as an attempt toclarify the extent of the scope of protection, though
it may include some inappropriate aspects.
When the two determination methods using
the doctrine of equivalents are analyzed from such a
viewpoint, the way in which the CAFC summed up– when an accused product having the samefunction is judged not to be an equivalent under§112, ¶6, on the basis of the difference in the timingof analysis, it is not an equivalent under thedoctrine of equivalents either, unless it is anafter-arising technology – is found to have been
extremely explicit and clear-cut. Because there
remains a problem that the significance of using thefunctional claim would be lost, i.e., the scope ofprotection becomes exactly the same as the casewhere the claim has been directly described by the
structure corresponding to the function, thefundamental error is likely to be in the approach of
applying the doctrine of equivalents itself, but it isconsidered to be an appropriate determination
method in that it can clarify the extent of thefunctional claim.
What about the method of expanding the scopeof protection by the doctrine of equivalents when
the function is not the same, but substantially thesame? Since this theory has only been applied in
two CAFC decisions, analysis can only be madebased on them, but some commonalities can befound between the two. Firstly, the invention was asoftware invention in both cases. Secondly,
infringement had been found by the district court inboth cases, the jury had found that the accused
product was equivalent to the embodimentcorresponding to the function. What impact dothese two common links have, and in what kind ofcase is the doctrine of equivalents applicable by thismethod?
Functional claims can roughly be divided into
two kinds based on the nature of the invention: aclaim in which the combination of functions is theimportant factor and the means for performing it
does not matter; and a claim in which the concretemeans performing the function is the importantfactor and the functional expression merely
expresses the means as a comprehensive concept.
Generally, the former can be more often found forsoftware inventions, and the latter for mechanicalinventions. Since the important factor for asoftware invention is its function, as long as the
combination of functions executing the invention is
described to the extent that can be enabled by aperson skilled in the art, the enabling requirement
would be met without needing to disclose detailed
programs. Meanwhile, a functionally describedclaim must correspond to the embodiment
disclosed in the specification according to §112, ¶6,
and in infringement litigation, the literal scope of asoftware invention described by functional
elements would be judged to be the machine
executing the algorithm, described in theembodiment as the structure corresponding to thefunction, as well as its equivalents. In other words,
although the important factor for a software
invention is the claim expressed by the functional
language as such, instead of the concrete means,the comparison will be made between the concretemeans and the accused product in thedetermination of literal infringement, and once theaccused product is judged not to be covered within
the scope of the embodiment and statutory
equivalents, the doctrine of equivalents will not beapplied unless it is an after-arising technology. Sucha narrow scope of protection would be contrary
both to the purport of including software inventions
into patentable subject matter as well as to the
purport of establishing §112, ¶6.
The above analysis reveals that the theory ofallowing application of the doctrine of equivalents
when the function is not the same, but substantiallythe same, is properly serving a supplementary role
as a means for saving inventions from imitators
who escape infringement by only making slightalterations to take advantage of the fact thatfunctional claims are interpreted in a limiting
manner, in cases where the function itself is● 141 ●IIP Bulletin 2003

relatively important.
However, such a precondition – the doctrine ofequivalents could be applicable based on substantial
identity of the function when the function itself isrelatively important – has not been indicated incourt decisions. Since this theory would also be
applicable to existing machines and otherinventions as well, is there a possibility that it
would actually be applied to such inventions,allowing the scope of protection to become
unlimitedly broad? In the case of a software
invention, it is easy to organically separate or
combine the functional element with otherelements, but in the case of a mechanical invention,
separation or combination of the functional
elements would make the corresponding structure
fundamentally different. Accordingly, in the case ofexisting mechanical and other inventions, evenwhen an accused product and the claim were judged
to have a substantially identical function, there
would be a relatively high possibility that the way
and the result will be judged to be different.
Nevertheless, as indicated by the second point incommon, the district court had found infringement
in both cases, and in that instance, the jury had
found the accused product to be equivalent to theembodiment corresponding to the function. In lightof this precondition, the CAFC merely allowed thedoctrine of equivalents on the basis that, although
literal infringement was denied because thefunction was different, the function was
substantially the same, and the two could beconsidered as statutory equivalents based on theabove precondition. Thus, it was not indicated as a
guideline on a determination method. Accordingly,
it may be too hasty to conduct such analysis atpresent.
As a conclusion, between the two guidelines
indicated for application of the doctrine ofequivalents to the scope of protection of functional
claims in the United States, the one based on thetiming of analysis has succeeded in clearlysumming up the extent of the scope of protectionof functional claims. On the other hand, thedetermination method for application of thedoctrine of equivalents based on substantial identityof the function involves the risks of also unlimitedly
expanding the extent of the scope of protection forexistent mechanical and other inventions, eventhough it is serving a supplementary role inprotecting inventions like software inventions inwhich the function itself is the important factor, so
attention should be paid to future trends of related
court decisions.
Japan is in the phase of accumulating court
decisions on determination standards for thedoctrine of equivalents, so it is not easy to conduct
a comparative study with the United States.

Nevertheless, although confusion occurred in the
United States due to the existence of a provision
under the statutory law, the extent of functional
claims is gradually being elucidated through the
CAFC’s accumulated efforts, and Japan has much tolearn from the course of development of suchdiscussions in the United States.

Ⅴ Closing Chapter
Literal expressions are inevitably ambiguousby nature, but inventors must express theirinventions in words. The words chosen by aninventor, a patent claim, could be expressed by
concrete things alone in some cases and would haveto include abstract expressions in other cases. If
abstract expressions were completely banned,
there would be inventions that cannot be properly
expressed, and if such expressions were overly
protected, it would diminish the motivation of athird person to develop new technology. Therefore,
when the literal claim language is too abstract tounderstand its true meaning, it is necessary tolearn the invention originally intended by theinventor by referring to the specification.
Interpretation of functional claims is considered toinclude such problems in which the basic conceptsof the relationship between freedom of expression
and appropriate interpretation are compressed.
In the United States where the existence of a
special provision on interpretation of functional
claims had brought about confusion, efforts havebeen made toward clarifying the standards throughaccumulation of case law. Thus, Japan, which has
been taking flexible actions due to lack of such aprovision, would be able to gain many useful
insights from the discussions in the UnitedStates(*23). While functional claims are frequently
used in inventions such as software inventions thatare characterized by the function itself, theapplication of the doctrine of equivalents based on
substantial identity of the function may serve therole to supplement the limiting interpretation of thefunctional claims in such fields of technology where
the function itself is important, so the theory of its
application should be analyzed even further byobserving the future trends of related court
decisions.

(*23) See Chapter IV of the report for the current situation in Japan.

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