A Simplified Explanation of the Effect of the Festo Case on Patent Rights

David Feigenbaum

(c) Fish & Richardson 2001, all rights reserved.

To be liable for infringing a patent, a company must be doing something that falls within the scope of at least one of the claims found at the end of the patent. For example, a claim that says the invention is "Any pencil that includes the combination of (a) a fir wood shaft surrounding a writing lead and (b) an eraser mounted on the end of the shaft," would cover typical fir wood pencils with erasers. This is simple enough.

But what if a company tries to get around the claim by using maple for the shaft. Would the claim be infringed even though the pencil shafts were not made of fir? Possibly yes under a commonly applied principle of fairness that allows the court to stretch the words "fir wood" to include other materials that are not substantially different from fir. This principle (called the doctrine of equivalents) prevents an infringer from sidestepping the patent on what some would see as a wording technicality.

How far the word "fir" could be stretched to cover other shaft materials depends partly on how the words of the claim may have been adjusted as part of the back and forth with the patent office before the patent was granted.

Suppose the original claim did not say what the shaft was made of, calling it simply a "shaft". The patent office may have refused to allow that claim because it was so broad as to describe caveman drawing instruments having corn-cob shafts surrounding coal. The inventor may then have added the words "fir wood" to the claim to get the patent office to grant the patent.

Then, because the claim was narrowed to avoid the old corn-cob drawing instrument, a doctrine of the law called "estoppel" would prevent the patent owner from ever later contending that his claim covers either corn-cob drawing instruments or devices that have shafts that are even more unlike fir wood than is corn-cob. But, as the law stood until recently, the owner of the patent could still rely on the doctrine of equivalents to assert his patent against the oak-shafted pencil and against an intermediate range of other equivalent shaft materials, such as compressed wood or wound paper, that are more similar to the claimed "fir wood" than were the old corn-cob instruments. In other words, when the inventor added the words "fir wood" he gave up some of the range of equivalent materials to which the claim might be applied, but he did not give up all of the range of equivalent materials.

This principle has been turned upside down by the recent Festo decision. Under Festo, when the inventor narrowed his claim from "shaft" to "fir wood shaft" to avoid the old corn cob device, he gave up the right to contend that the claim extended to ANY shaft material other than fir wood. There is no longer any permitted range of equivalents. (Other kinds of changes to the claims will also cut off the right to equivalents if they are made to get the patent office to agree to grant a patent.) The Festo rule makes it easier for a possible infringer to know whether he infringes the claim, even though it may limit the patent owner to the actual words of his claim.

Thus, the specific claim wording changes that are made during the examination of the patent in the patent office have become more important to the question of how far the claims will later be interpreted to extend.

The Supreme Court has agreed to hear an appeal of the Festo case, with a decision expected in mid-2002. Many observers believe the decision will be reversed.