The Doctrine of Equivalents Lives On in Supreme Court Patent Decision

On March 3, 1997, the United States Supreme Court rendered its anxiously awaited patent law opinion in Warner-Jenkinson Company, Inc. v. Hilton Davis Chemical Co. This case involves the very complex "doctrine of equivalents." At risk of oversimplification, this doctrine holds that a patented invention is protected by its patent claims not only against devices or processes with identical descriptions (called "literal infringement"), but also against those which perform substantially the same function in substantially the same way to yield substantially the same result, even though there is some difference in elements of the two inventions. The patent claims, in other words, can be found to cover things not actually disclosed by the precise terms of the claims as allowed by the United States Patent Office.

It has long been argued that the doctrine of equivalents as applied by the courts has increased the number of patent infringement cases filed and resulted in a broadening of the scope of the claims when litigated.

While the Supreme Court's decision does not change the doctrine in any substantive way, it does establish a methodology for applying the doctrine to particular claims. That test requires examination of each element of the allegedly infringed claim, rather than the overall effect. Not every combination of devices or steps that produces the same effect as another combination is necessarily the same as the other. (Consider, for example, a fountain pen and a ballpoint pen: very different combinations of parts producing the same result.) Rather, it is the mere substitution of one element for another in an essentially identical invention that offends the patent.

This decision may allow courts to change individual elements of a claim without enlarging the scope of a patent beyond that of the specific claims allowed by the Patent Office. Its application will require more scrutiny of the underlying concept of an invention to guard against the broadening of the overall effect of the patent.

C. Fred Rosenbaum
Mr. Rosenbaum is a Senior Attorney in the Firm
E-mail: frosenba@woodsrogers.com