Washington Law Review


In Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., the Federal Circuit adopted a strict approach to prosecution history estoppel and thereby limited the availability of the doctrine of equivalents to patentees suing for infringement by after-arising technology. The court held that when a narrowing claim amendment creates prosecution history estoppel, the amended claim element maintains no range of equivalents and therefore the patentee is completely barred from applying the doctrine of equivalents. The court rejected the flexible approach, which allows a scope of equivalents even after a narrowing claim amendment. This Note argues that the Supreme Court should overrule the Festo decision and adopt the flexible approach to prosecution history estoppel in cases of infringement by after-arising technology. The strict approach adopted by Festo hinders the doctrine of equivalents in protecting patentees from infringement by after-arising technology. The Festo majority misinterpreted the Supreme Court's opinion in Warner-Jenkinson Co. v. Hilton Davis Chemical Co., which implies that a scope of equivalents is available after a narrowing claim amendment has been made for patentability reasons. In addition, the Festo decision leads to incongruous results with respect to after-arising technology, as it protects unamended claims but not amended claims, and predictable arts but not unpredictable arts. Furthermore, Festo conflicts with patent policy, which rewards pioneer inventions with a broad range of equivalents. Finally, this flexible approach would give patentees fair protection from infringement by after-arising technology under the doctrine of equivalents.

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