Does a patent mean more than it says, or more accurately, does the protection afforded by a patent exceed the literal meaning of the claim language? The short answer is yes! For many years, the meaning of patent claims has been expanded beyond its literal scope under the judicially created "doctrine of equivalents." The doctrine is intended to prevent a competitor from avoiding infringement of a patent's claims merely by making insubstantial changes to the patented design. Thus, while the doctrine may be viewed positively by patent holders, it makes it difficult for good-faith competitors to determine whether their product will infringe on another patent.
In the past, courts have put limits on how far the scope of the claims can be expanded under the doctrine of equivalents. Claims cannot be interpreted so broadly that they would read on devices known before the claimed invention was made. Also, claims cannot be expanded to exclude a limitation which the inventor introduces for the purpose of obtaining allowance of a claim. However, if the inventor introduced two claim limitations to obtain allowance of the claim, but only one of the limitations was needed to distinguish over the prior art, is the inventor prevented from later expanding the interpretation of the claims to include the unnecessary limitation?
In the summer of 1995, the United States Court of Appeals for the Federal Circuit -- which hears all appeals of patent infringement cases -- said "no" to this very question in Hilton Davis Chemical Co. v. Warner-Jenkinson Co., Inc. Arguably inconsistent with past Federal Circuit and Supreme Court decisions, Hilton Davis suggests that a patent's claims can be expanded very generously beyond their literal scope. The decision, which many feel injects still greater uncertainty into infringement analysis, is now being reviewed by the United States Supreme Court. Arguments from the parties were heard last fall, and it is hoped that the Supreme Court's decision this Term will provide appropriate limits on theapplication of the doctrine of equivalents.