The Doctrine of Equivalents is one of the most difficult-to-understand
issues regarding patent en-forcement and interpretation.
Simply stated, patent claims--that is, the numbered paragraphs at the end of the patent--measure the scope of protection that a patent offers.
Many argue that a properly interpreted scope of protection should represent the literal language of a patent's claims, and that this scope of protection should be limited to the literal language.
But, the courts suggest that, if we maintain this limitation, we risk the chance of a patent being fraudulently avoided. For instance, what if minor changes to a device create controversy because the exact words of the patent's claims did not specifically state the changes?
To guard against this possibility, the courts developed the Doctrine of Equivalents. The Doctrine is much like a gray area that surrounds the claims of a patent to broaden the scope of the patent's protection.
The gray area. In a typical situation, one obtains a patent on an invention. Another inventor develops a similar, but not identical, device. The former inventor has designed his/her invention with respect to the literal language of the patent's claims. The question that arises is whether the Doctrine of Equivalents will permit the latter device to fall under the scope of protection of the former device's patent.
Other questions regarding the Doctrine of Equivalents include:
When does the Doctrine come into play?
Recent court decisions attempt to answer these questions, but, it does appear that the Doctrine of Equivalents is to be narrowly interpreted, and the decision to rely on the Doctrine to establish a patent's scope of protection or infringement upon that scope must be well thought out and cautious.
What to consider. Generally speaking, the extent to which the Doctrine of Equivalents can broaden a scope of protection depends on the nature of the art in question and the actions of the applicant in obtaining his/her patent, both of which can be used to determine to what extent the Doctrine applies.
For all intents and purposes, one cannot evaluate the scope of the Doctrine of Equivalents without also knowing the content of the prior art and reviewing the actions of the applicant in obtaining that patent.
When evaluating the user of the Doctrine of Equivalents, one should also consider whether the Doctrine applies to the claim as a whole or only a single element of the claim.
In discussing the Doctrine of Equivalents, I have only brushed the surface; however, one needs to be aware that the Doctrine of Equivalents exists and that conclusions drawn about the Doctrine are complicated and based upon numerous judgments.