More than 50 years ago, the U.S. Supreme Court enunciated the modern doctrine of equivalents, which provides a patentee with a scope of patent protection beyond what the literal text of the patent’s claims would otherwise afford.[1]� Under this doctrine, even though an accused article or method may not literally infringe a patent claim, infringement may still be found if the accused article or method is “equivalent” to or substantially the same as the claimed invention – if the differences between the claimed “invention” and the accused product or process are “insubstantial.”[2]� The purpose of the doctrine is to ward off the crafty infringer who makes a subtle insubstantial and insignificant substitution or change in order to avoid the literal text of the claim but still practice the invention.

The doctrine of equivalents brings to focus an increased tension between competing policies underlying our patent laws. On one hand, patents serve a role in providing notice of the scope of the patentee’s rights to competitors – as this column has stated in the past, a patent’s claims not only should define what is covered by the patent but by doing so should provide notice as to what is not covered, i.e., what competitors can and cannot do. On the other hand, a patentee should be afforded some protection against the shifty infringer who attempts to avoid liability simply by playing semantic games to avoid the literal text of a patent. The tension between these competing policies was exacerbated by the issuance of two arguably conflicting opinions by the Federal Circuit within a span of two years.

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