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On the Decline of the Doctrine of Equivalents

Lee Petherbridge

Loyola Law School Los Angeles

April 30, 2010

Cardozo Law Review, Vol. 31, No. 4, 2010
Loyola-LA Legal Studies Paper 2010-25

The doctrine of equivalents is a judicial creation that allows patentees to exclude others from the use of subject matter beyond the textual scope of a patent’s claims. This venerable – and extremely controversial – doctrine is tolerated (or promoted) on the theory that it is fundamentally necessary to protect the incentive structure of the patent system.

The perceived importance of the doctrine of equivalents makes all the more remarkable recent scholarly arguments that this ancient doctrine is a dead letter in American patent law. One recent empirical study argues that the doctrine is dead but hypothesizes that it did not succumb because courts acted to restrict it; indeed, it argues that the legal rules of the doctrine simply do not much matter. The hypothesis instead emphasizes that the doctrine succumbed because changes in the procedural circumstances in which equivalents claims are heard caused courts to lump them together with literal infringement determinations, making it more likely that they would be resolved in the same way – against the patentee.

This Article uses empirical techniques to independently test this hypothesis. It first develops evidence that supports the contention that the doctrine of equivalents has indeed been in decline over the last fifteen years. It then establishes detailed evidence for two additional findings. The first is that procedural context contributes to the decline of the doctrine. The second, however, is that the legal rules imposed by courts to restrict the doctrine also contribute. The Article interprets the results to mean that the decline of the doctrine of equivalents is something more than just the happy (or unhappy) accident of the procedural context in which equivalents claims are now litigated. It is the culmination of a concerted and prolonged court-driven effort to make its favorable application the exception, not the rule.

Number of Pages in PDF File: 36

Keywords: Patents, Doctrine of Equivalents, Courts, Federal Circuit, Jurisprudence, Doctrinal Development, Legal Rules, Legal Realism

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Date posted: May 4, 2010 ; Last revised: May 22, 2010

Suggested Citation

Petherbridge, Lee, On the Decline of the Doctrine of Equivalents (April 30, 2010). Cardozo Law Review, Vol. 31, No. 4, 2010; Loyola-LA Legal Studies Paper 2010-25. Available at SSRN: http://ssrn.com/abstract=1598549

Contact Information

Lee Petherbridge (Contact Author)
Loyola Law School Los Angeles ( email )
919 Albany Street
Los Angeles, CA 90015-1211
United States
213-736-8194 (Phone)
213-380-3769 (Fax)
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