A Penguin’s Defense of the Doctrine of Equivalents: Applying Cognitive Linguistics To Patent Law
There is no dearth of commentary about the doctrine of equivalents in patent law.1 Many articles proclaim the doctrine’s death, often noting its passage with unbridled delight.2 Some articles provide empirical evidence to support the assertion that the doctrine of equivalents is dead.3 Others simply yearn for the doctrine to fade from use, pointing out that no court has “articulated a convincing rationale” for the doctrine’s continued use.4 But maybe these scholars have it wrong. It may be true that the instances of doctrine of equivalents analysis in patent cases are on the decline and successful outcomes based on the doctrine waning further. But these observations tell only a small part of the story. This Article contends that, despite evidence to the contrary, the death of the doctrine of equivalents has been greatly exaggerated.5
The birth of the doctrine of equivalents was noble enough; it was created to soften the blow associated with literal interpretation of patent claim terms. During patent litigation, claims of the patent are generally construed as lists of necessary and sufficient features or conditions. During infringement analysis, if each and every claimed feature or condition is found in the accused device or process, infringement is found. Infringement, then, can be viewed like traditional set theory, where an object is deemed a member of a class if it meets the required attributes of the class.6 The discontent with this system comes when the accused device or process does not squarely satisfy each of the features or conditions of the claim, yet is essentially the same as the patented invention. Courts have been loath to excuse infringers who take the essence, if not the exact parameters, of the patented invention, whether intentionally or not.7 The doctrine of equivalents was thus crafted to permit a finding of infringement, even where the accused device or process does not literally infringe the claim and to prevent an infringer from avoiding liability by making trivial changes.8
The aspirations of the doctrine, however, reach farther. Effective application of the doctrine eases the difficulty of describing and defining the boundaries of new inventions using words.9 The doctrine moderates the differences between what the inventor invented, what the patent claims, and what of the invention could reasonably be described in the words of the claim.10 But if the doctrine of equivalents is dead, as many contend, where does that leave us?
