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13 Fed. Cir. B.J. 75 (2003-2004)
The Doctrine of Equivalents: Both a Sword and a Shield

handle is hein.journals/fedcb13 and id is 89 raw text is: The Doctrine of Equivalents:
Both a Sword and a Shield
George M. Sirilla, Thomas P. Feddo, and Michael C. Antone*
Introduction
The patentee may bring the defendant within the letter ofhis claims, but if the latter has
so far changed the principle ofthe device that the claims of the patent, literally construed,
have ceased to represent his actual invention, he is as little subject to be adjudged an
infringer as one who has violated the letter of a statute has to be convicted, when he has
done nothing in conflict with its spirit and intent.'
And so it was established over 100 years ago that the doctrine of equivalents
(DOE) can be used defensively, as a shield, to establish non-infringement
(sometimes referred to as the reverse doctrine of equivalents (RDOE)) as well
as offensively, as a sword, to establish infringement.
While the use of the DOE as a sword has been analyzed systematically and
extensively by the legal community,2 other aspects of the DOE when used as
a shield have likewise had a long history in patent jurisprudence, and yet they
have not received as much attention.' This article explores two such aspects
of the DOE, namely: (1) that the DOE is a viable and legally sound defense
when the accused device falls within the letter of [the patentee's] claims4;
and (2) that whether used as a sword or a shield, the same analysis must be
made, namely, whether the accused device and/or the elements thereof can
fairly be said to be equivalent to the claimed subject matter considered in light
of the invention as disclosed in the patent's specification (written description
* Mr. Sirilla and Mr. Feddo are attorneys with Pillsbury Winthrop LLP. Mr. Antone is the
Intellectual Property Counsel of Corvis Corporation. The authors would like to acknowledge
with appreciation the helpful research and analysis performed by Kerry T. Hartman, an
attorney with Pillsbury Winthrop, and the research by Noah Webster, a 2002 summer
associate at Pillsbury Winthrop.
'Westinghouse v. Boyden Power Brake Co., 170 U.S. 537, 568 (1898) (emphasis added).
2 See, e.g., Sanitary Refrigerator Co. v. Winters, 280 U.S. 30, 41-42, 3 U.S.P.Q. 40, 44
(1929); Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 U.S. 605, 608, 85 U.S.P.Q.
328, 330 (1950).
1 Indeed, there seems to be a misconception in some quarters that the use of the DOE as
a shield to defeat a patentee's case has been rare since Westinghouse. As this article will
demonstrate, however, the courts have been consistent and unanimous in affirming and
upholding this defense in numerous cases.
' Westinghouse, 170 U.S. at 568.

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