Cite as: 520 U. S. 17 (1997)
Opinion of the Court
rendered the claimed subject matter unpatentable. Thus, in Exhibit Supply Co. v. Ace Patents Corp., 315 U. S. 126 (1942), Chief Justice Stone distinguished inclusion of a limiting phrase in an original patent claim from the "very different" situation in which "the applicant, in order to meet objections in the Patent Office, based on references to the prior art, adopted the phrase as a substitute for the broader one" previously used. Id., at 136 (emphasis added). Similarly, in Keystone Driller Co. v. Northwest Engineering Corp., 294 U. S. 42 (1935), estoppel was applied where the initial claims were "rejected on the prior art," id., at 48, n. 6, and where the allegedly infringing equivalent element was outside of the revised claims and within the prior art that formed the basis for the rejection of the earlier claims, id., at 48.5
It is telling that in each case this Court probed the reasoning behind the Patent Office's insistence upon a change in the claims. In each instance, a change was demanded because the claim as otherwise written was viewed as not describing a patentable invention at all—typically because what it described was encompassed within the prior art. But, as the United States informs us, there are a variety of other reasons why the PTO may request a change in claim language. Brief for United States as Amicus Curiae 22-23
5 See also Smith v. Magic City Kennel Club, Inc., 282 U. S. 784, 788 (1931) (estoppel applied to amended claim where the original "claim was rejected on the prior patent to" another); Computing Scale Co. of America v. Automatic Scale Co., 204 U. S. 609, 618-620 (1907) (initial claims rejected based on lack of invention over prior patents); Hubbell v. United States, 179 U. S. 77, 83 (1900) (patentee estopped from excluding a claim element where element was added to overcome objections based on lack of novelty over prior patents); Sutter v. Robinson, 119 U. S. 530, 541 (1886) (estoppel applied where, during patent prosecution, the applicant "was expressly required to state that [the device's] structural plan was old and not of his invention"); cf. Graham v. John Deere Co. of Kansas City, 383 U. S. 1, 33 (1966) (noting, in a validity determination, that "claims that have been narrowed in order to obtain the issuance of a patent by distinguishing the prior art cannot be sustained to cover that which was previously by limitation eliminated from the patent").
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