MPEP 2173.01
Interpreting the Claims

Ninth Edition of the MPEP, Revision 07.2022, Last Revised in February 2023

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2173.01    Interpreting the Claims [R-10.2019]

[Editor Note: This MPEP section is applicable to applications subject to the first inventor to file (FITF) provisions of the AIA except that the relevant date is the "effective filing date" of the claimed invention instead of the "time of the invention," which is only applicable to applications subject to pre-AIA 35 U.S.C. 102. See 35 U.S.C. 100 (note) and MPEP § 2150 et seq.]

A fundamental principle contained in 35 U.S.C. 112(b) or pre-AIA 35 U.S.C. 112, second paragraph is that applicants are their own lexicographers. They can define in the claims what the inventor or a joint inventor regards as the invention essentially in whatever terms they choose so long as any special meaning assigned to a term is clearly set forth in the specification. See MPEP § 2111.01. Applicant may use functional language, alternative expressions, negative limitations, or any style of expression or format of claim which makes clear the boundaries of the subject matter for which protection is sought. As noted by the court in In re Swinehart, 439 F.2d 210, 160 USPQ 226 (CCPA 1971), a claim may not be rejected solely because of the type of language used to define the subject matter for which patent protection is sought.


The first step to examining a claim to determine if the language is definite is to fully understand the subject matter of the invention disclosed in the application and to ascertain the boundaries of that subject matter encompassed by the claim. During examination, a claim must be given its broadest reasonable interpretation consistent with the specification as it would be interpreted by one of ordinary skill in the art. Because the applicant has the opportunity to amend claims during prosecution, giving a claim its broadest reasonable interpretation will reduce the possibility that the claim, once issued, will be interpreted more broadly than is justified. In re Yamamoto, 740 F.2d 1569, 1571, 222 USPQ 934, 936 (Fed. Cir. 1984); In re Zletz, 893 F.2d 319, 321, 13 USPQ2d 1320, 1322 (Fed. Cir. 1989) ("During patent examination the pending claims must be interpreted as broadly as their terms reasonably allow."). The focus of the inquiry regarding the meaning of a claim should be what would be reasonable from the perspective of one of ordinary skill in the art. In re Suitco Surface, Inc., 603 F.3d 1255, 1260, 94 USPQ2D 1640, 1644 (Fed. Cir. 2010); In re Buszard, 504 F.3d 1364, 84 USPQ2d 1749 (Fed. Cir. 2007). In Buszard, the claim was directed to a flame retardant composition comprising a flexible polyurethane foam reaction mixture. Buszard, 504 F.3d at 1365, 84 USPQ2d at 1749. The Federal Circuit found that the Board’s interpretation that equated a "flexible" foam with a crushed "rigid" foam was not reasonable. Id. at 1367, 84 USPQ2d at 1751. Persuasive argument was presented that persons experienced in the field of polyurethane foams know that a flexible mixture is different than a rigid foam mixture. Id. at 1366, 84 USPQ2d at 1751. See MPEP § 2111 for a full discussion of broadest reasonable interpretation.

Under a broadest reasonable interpretation, words of the claim must be given their plain meaning, unless such meaning is inconsistent with the specification. The plain meaning of a term means the ordinary and customary meaning given to the term by those of ordinary skill in the art at the time of the invention. The ordinary and customary meaning of a term may be evidenced by a variety of sources, including the words of the claims themselves, the specification, drawings, and prior art. However, the best source for determining the meaning of a claim term is the specification - the greatest clarity is obtained when the specification serves as a glossary for the claim terms. The presumption that a term is given its ordinary and customary meaning may be rebutted by the applicant by clearly setting forth a different definition of the term in the specification. In re Morris, 127 F.3d 1048, 1054, 44 USPQ2d 1023, 1028 (Fed. Cir. 1997) (the USPTO looks to the ordinary use of the claim terms taking into account definitions or other "enlightenment" contained in the written description); But c.f. In re Am. Acad. of Sci. Tech. Ctr., 367 F.3d 1359, 1369, 70 USPQ2d 1827, 1834 (Fed. Cir. 2004) ("We have cautioned against reading limitations into a claim from the preferred embodiment described in the specification, even if it is the only embodiment described, absent clear disclaimer in the specification."); In re Bigio, 381 F.3d 1320, 1325, 72 USPQ2d 1209, 1211 (Fed. Cir. 2004) (The claims at issue were drawn to a "hair brush." The court upheld the Board’s refusal to import from the specification a limitation that would apply the term only to hairbrushes for the scalp. "[T]his court counsels the PTO to avoid the temptation to limit broad claim terms solely on the basis of specification passages."). When the specification sets a clear path to the claim language, the scope of the claims is more easily determined and the public notice function of the claims is best served. See MPEP § 2111.01 for a full discussion of the plain meaning of claim language.

If an Office action has issued where the plain meaning of the claim terms was used, applicant may point out that the term has been given a special definition. Since there is a presumption that claim terms are given their plain meaning, and the use of special definitions is an exception, the applicant must point to where the specification as filed provides a clear and intentional use of a special definition for the claim term to be treated as having a special definition.

An applicant may not add a special definition or disavowal after the filing date of the application. However, an applicant may point out or explain in remarks where the specification as filed contains a special definition or disavowal.


As part of the claim interpretation analysis, examiners should determine whether each limitation invokes 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph or not. If the claim limitation invokes 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, the claim limitation must "be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof." 35 U.S.C. 112(f) and pre-AIA 35 U.S.C. 112, sixth paragraph; see also In re Donaldson Co., 16 F.3d 1189, 1193, 29 USPQ2d 1845, 1849 (Fed. Cir. 1994) (en banc) ("[W]e hold that paragraph six applies regardless of the context in which the interpretation of means-plus-function language arises, i.e., whether as part of a patentability determination in the PTO or as part of a validity or infringement determination in a court."). See MPEP § 2181, subsection I. for more information regarding the determination of whether a limitation invokes 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph, and means- (or step-) plus- function claim limitations.