By Edward J. Marshall of DLA Piper US LLP
A few other attorneys and I were discussing how statements in a patent’s file history affect claim construction. During this discussion, as in almost every discussion about a patent’s file history, the question of “prosecution history estoppel” came up. Why, I thought, were we discussing prosecution history estoppel in the context of claim construction? One of the other attorneys attempted to explain that prosecution history estoppel prevents a patentee from amending his claims and later attempting to assert those claims in a way that is inconsistent with the amendment. His answer, while a technically correct statement of fact, didn’t actually answer the question. Prosecution history estoppel does prevent asserting a claim in a manner inconsistent with earlier amendments, but only to the extent of limiting the scope of equivalent elements available under the doctrine of equivalents.
A few months later, a related question brought the proper role of prosecution history estoppel issue to the forefront again. I was asked, “If prosecution history estoppel does not prevent a patentee from surrendering subject matter and later asserting that his claims cover the surrendered subject matter, what does?” This question, like the attempted explanation discussed above, slightly misses the point. Pros...