The Doctrine of Equivalents

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By Rich Stim

The doctrine of equivalents is a secondary method for deciding whether a patent is being infringed. Instead of a straight infringement claim -- in which the infringing invention "reads" directly oin the patented invention claims -- the doctrine of equivalents considers whether a later device or process does the same work in substantially the same way to accomplish the same result as a patented invention. If it does, then patent infringement will be found to exist.

The primary method used by the courts to assess possible patent infringement is to compare the literal language of each element of the patent’s claims with each element of the device or process claimed to be infringing. (In patent jargon, do the patent claims “read on” the infringing device or process?) However, even if a patent’s claims don’t literally “read on” an allegedly infringing device or process, infringement may be found under the doctrine of equivalents so long as the element of the device is the “equivalent” of the claimed element. A device element is equivalent if it performs the same function in the same way to achieve the same result as the claim element, or the role of the device element is substantially the same as that of the claim element.

The doctrine of equivalents is intended to prevent designing around a patent on hyper-technical grounds. Unfortunately, there is no logical dividing line between (1) noninfringement based on legitimate designing around an invention, and (2) infringement based on the doctrine of equivalents. It is up to the courts to decide, on a case-by-case basis, if inventions are substantially equivalent.

In 2000, a federal appeals court barred the use of the doctrine of equivalents for any amended patent claims. In 2002, the U.S. Supreme Court struck down this absolute bar to the doctrine of equivalents and replaced it with a less--arbitrary standard. Under the Supreme Court’s standard, all amended claims are presumed to be narrowed so as to bar the doctrine of equivalents. But this presumption can be rebutted if a patent owner can demonstrate that the amendment involved a feature that was “unforeseeable at the time of the application” or “for some other reason” could not be included in the original claim. In that case, the patent owner can use the doctrine of equivalents. (Festo Corp. v. Shoketsu Kinzoku Kabushiki Co. Ltd., 535 U.S .722 (2002).)