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Prosecution History Disclaimer: Beware of What You Clearly and Unambiguously Say

By Jonathan S. Caplan and Benu Mehra

Patent prosecutors typically are cautious when making arguments that distinguish their client's invention from the prior art. This caution was traditionally based on the concern that later, when the client enforced its patent rights against a potential infringer, these arguments may provide the basis for restricting the range of equivalents available to the patentee under the doctrine of prosecution history estoppel. Prosecution history estoppel normally limits the range of equivalent elements that are available to satisfy a claim element under a doctrine of equivalents analysis (ie, when there is no literal infringement of that claim element). Recent decisions by the Federal Circuit not only reaffirm the significance of statements made during prosecution; they also extend their impact to a literal infringement analysis. A patentee who during prosecution “clearly and unequivocally” disavows the prior art (or even defines the invention) may affect the literal scope of the claims. This doctrine is now regularly referred to as prosecution history disclaimer.

Under this doctrine, a claim term may receive a “gloss” that limits the claim to a particular feature that is not expressly stated in the claim, and the result can play out at the level of a literal infringement analysis. Thus, an accused infringer should closely examine prosecution history statements, not only as a source of arguments to limit the patentee's range of equivalents, but also as a source of potentially determinative evidence for a favorable claim construction to avoid literal infringement. Similarly, patent prosecutors should carefully phrase the arguments made during prosecution so as to avoid unnecessarily emphasizing arguments or distinctions in order to obtain allowance of claims, thereby limiting the opportunity of a future alleged infringer to successfully invoke the doctrine of prosecution history disclaimer.

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