In Another Round of the Festo Case, the Federal Circuit Holds That Foreseeable Equivalents Are Those Known in the Field of Invention

Case: Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd. (Fed. Cir. No. 05-1492

The One Sentence Summary: Foreseeability for application of prosecution history estoppel applies when the equivalent surrendered by an amendment was known in the field of invention.


Federal Circuit Holdings:

• Prosecution history estoppel prevents application of the doctrine of equivalents to capture equivalents that were surrendered by amendment during prosecution. Amendments to claims surrender scope when they are made for a reason related to patentability. Under the Supreme Court's decision in Festo, amendments are related to patentability unless they fall within one of the following exceptions: (1) the equivalent was “unforeseeable at the time of the application,” (2) “the rationale underlying the amendment [bears] no more than a tangential relation to the equivalent in question,” or (3) that “some other reason suggest[s] that the patentee could not reasonably be expected to have described the insubstantial substitute in question.” Festo VIII, 535 U.S. at 740-41.
• Foreseeability under the first exception does not require that patentee understand how application of the function/way/result test of the doctrine of equivalents will work as to the claimed equivalent. Rather, an equivalent is foreseeable if it was known and disclosed in the pertinent prior art in the field of invention.