By Mr Joshua Krumholz & Mr Todd S. Parkhurst
On May 28, 2002, the Supreme Court reversed in substantial part the controversial decision of the Federal Circuit in Festo Corp. v. Shoketsu Kihzoka Kogyo Kabushiki Co., Ltd. At the heart of its decision lay a disagreement with the Federal Circuit over the proper scope of a legal principle known as the doctrine of equivalents. In Festo Corp., the Federal Circuit dramatically scaled back the application of that principle. As a result, the value of many patents was substantially reduced, and proving infringement of those patents became much more difficult. By rejecting the Federal Circuit's approach, the Supreme Court essentially reaffirmed prior law.
The Application of the Doctrine of Equivalents
The doctrine of equivalents is a principle applied when determining potential infringement of a patent. Under U.S. patent law, a patent may be infringed either literally -- where every element in a patent claim is literally found in an accused product -- or by equivalents -- where the product varies to some degree from the actual claim, but the difference is insubstantial. The doctrine of equivalents was created in recognition of the fact that language does not always capture in full the essence of an invention. The doctrine of equivalents protected patent holders from efforts by competitors to exploit the inherent limits of language by making only slight or insignificant changes to the invention claimed in the patent.
The problem with this approach, however, was the uncertainty that resulted. If an innovator with a new idea could be sued for something "equivalent" to a claimed invention, it became harder to predict the boundaries of that patent. To temper this concern, the Supreme Court previously had held that the public may look to the public record behind the patent to better understand its limitations. Known as prosecution estoppel, the Supreme Court previously held that patent holders would be limited by the representations they made to the Patent & Trademark Office (PTO) to get their patent allowed. If a patent holder "gave up" a portion of its claim in order to persuade the PTO to allow its patent (for instance, if it narrowed the scope of its claimed invention to avoid a claim that someone had already conceived of the invention), the patent holder could not later claim infringement by practicing in the same area that the patent holder had disclaimed.
The Federal Circuit's Decision in Festo...