Invention, Refinement and Patent Claim Scope: A New Perspective on the Doctrine of Equivalents

INTRODUCTION

Perhaps no doctrine in patent law is as controversial1 as the Doctrine of Equivalents (DOE),2 a common law creation that allows a court to expand patent scope beyond the rights literally claimed in the patent.3 Despite nearly two hundred years of development,4 patent law lacks a coherent vision of a doctrine that holds great intuitive appeal.5 Debate about the proper contours of the DOE is formal and unsatisfying because the doctrine lacks a strong normative foundation. This Article supplies a rigorous justification for the DOE that explains when it should apply and why its application should be "the exception . . . not the rule."6

The traditional justification explains that the DOE prevents "an unscrupulous copyist" from skirting patent claim language by making insignificant, yet non-infringing, changes in the technology.7 This fairness theory seems to be loosely based on a Lockean notion that an inventor should be justly rewarded for her labors.8 One version of the fairness theory treats the DOE as a cure for mistakes by the Patent Office that improperly limit patent scope.9 Another version treats the DOE as a way to reverse the unjust enrichment of a competitor who profits from the patent and does little or nothing to advance the technology.10