Devoted to Corporate Attorneys, Corporate Lawyers, and Corporate Counsel

The following is not meant to be legal advice.

On July 5, 2007, the Federal Circuit issued a decision in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co. (No. 05-1492), concluding that the foreseeability test does not require knowledge that the alternative would satisfy the function, way, result, or insubstantial differences test.

The Federal Circuit explained that the test was designed to determine whether an alternative was close enough to the claimed invention to be an equivalent.  The test is not designed to determine whether subject matter was surrendered during prosecution of the patent. Use of the test for determining foreseeability and equivalency would lead to inconsistencies requiring the patentee to argue that the alternative did not satisfy the test and was unforeseeable, but later argue the alternative does satisfy the test in claiming infringement under the doctrine of equivalents.

The Federal Circuit stated the alleged equivalent accused by Festo was surrendered during prosecution of the patent in suit.  If an amendment was made during prosecution relating to patentability, prosecution history estoppel bars the application of the doctrine of equivalents with respect to that element.