Cite as: 520 U. S. 17 (1997)
Syllabus
subject matter, even if it is equivalent to the matter expressly claimed. But petitioner reaches too far in arguing that any such surrender establishes a bright line beyond which no equivalents may be claimed, and that the reason for an amendment during patent prosecution is therefore irrelevant to any subsequent estoppel. There are a variety of reasons why the PTO may request a change in claim language, and if the patent holder demonstrates that an amendment had a purpose unrelated to patentability, a court must consider that purpose in order to decide whether an estoppel is precluded. Where the patent holder is unable to establish such a purpose, the court should presume that the purpose behind the required amendment is such that prosecution history estoppel would apply. Here, it is undisputed that the upper limit of 9.0 pH was added to the '746 patent in order to distinguish the Booth patent, but the record before this Court does not reveal the reason for adding the lower 6.0 pH limit. It is therefore impossible to tell whether the latter reason could properly avoid an estoppel. Pp. 30-34. (e) The Court rejects petitioner's argument that Graver Tank requires judicial exploration of the intent of the alleged infringer or a case's other equities before allowing application of the doctrine of equivalents. Although Graver Tank certainly leaves room for the inclusion of intent-based elements in the doctrine, the Court does not read the case as requiring proof of intent. The better view, and the one consistent with Graver Tank's predecessors, see, e. g., Winans v. Denmead, 15 How. 330, 343, and the objective approach to infringement, is that intent plays no role in the doctrine's application. Pp. 34-36.
(f) The Court also rejects petitioner's proposal that in order to minimize conflict with the notice function of patent claims, the doctrine of equivalents should be limited to equivalents that are disclosed within the patent itself. Insofar as the question under the doctrine is whether an accused element is equivalent to a claimed element, the proper time for evaluating equivalency—and knowledge of interchangeability between elements—is at the time of infringement, not at the time the patent was issued. P. 37. (g) The Court declines to consider whether application of the doctrine of equivalents is a task for the judge or for the jury, since resolution of that question is not necessary to answer the question here presented. Pp. 37-39. (h) In the Court's view, the particular linguistic framework used to determine "equivalence," whether the so-called "triple identity" test or the "insubstantial differences" test, is less important than whether the test is probative of the essential inquiry: Does the accused product or process contain elements identical or equivalent to each claimed element of the patented invention? Different linguistic frameworks
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