Doctrine of equivalents

The doctrine of equivalents is a legal rule in many (but not all) of the world's patent systems that allows a court to hold a party liable for patent infringement even though the infringing device or process does not fall within the literal scope of a patent claim, but nevertheless is equivalent to the claimed invention. U.S. Judge Learned Hand has described its purpose as being "to temper unsparing logic and prevent an infringer from stealing the benefit of the invention".

German courts typically apply a three-step test known as Schneidmesser's questions. These questions are:

All of the above questions need to be answered in the affirmative in order to demonstrate equivalent infringement. In addition, an allegation of equivalent infringement needs to withstand the Formstein test. The corresponding question reads:

Ireland appears to subscribe to a doctrine of equivalents. In Farbwerke Hoechst v Intercontinental Pharmaceuticals (Eire) Ltd (1968), a case involving a patent of a chemical process, the High Court found that the defendant had infringed the plaintiff's patent despite the fact that the defendant had substituted the starting material specified in the patent claim for another material. Expert evidence showed that any technician who failed to obtain a good result using the specified starting material would try the replacement material. The two materials were therefore held to be chemically equivalent, and the replacement of one with the other by the defendant did not prevent a finding and injunction against him.

On 21 March 2013, the Federal Patent Court of Switzerland adopted an approach similar to the three-prong test applied in Germany. The court based its decision on the three questions:

The court denied equivalent infringement of EP0918791B3, since paragraph 19 of EP0918791B3 explicitly teaches that toxic chromium compounds may be replaced by metallic catalysts. A person skilled in the art would not consider the organic catalyst TEMPO as a solution of equal value to the ruthenium salts specified in claim 1. The answer to the third question was negative.

The court also ruled that there was equivalent infringement of EP1149840B1, since all questions of the three-prong test were answered in the affirmative. The court set forth that the replacement of the claimed p-Toluenesulfonic acid with pyridine/water constituted basic knowledge taught during the first years of an undergraduate course in organic chemistry.

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