The doctrine of equivalents is a way to find infringement even when none literally exists. If a new invention is substantially similar to a patented invention but does not technically infringe on the claims of the patented invention, you can use the doctrine of equivalents to prove infringement.

How Can I Prove Infringement Using the Doctrine of Equivalents?

To prove infringement using the doctrine of equivalents, you must prove two kinds of equivalence:

  • Element-by-element equivalence – every element of the patented invention must be either present or have an equivalent in the new invention.
  • Overall equivalence – the invention must perform substantially the same function in substantially the same way to infringe on the patented invention.

If the invention has element by element equivalence, but does not perform substantially the same function, or does so in a different way, it may not infringe under the doctrine of equivalents. Similarly, if the new invention seems to perform the same function in the same way as the patented invention but does not have all the elements or their equivalents, the new invention will probably not be found to infringe.

What Does it Mean for an Element to be Equivalent?

An element is equivalent if the difference between it and the patented invention would be insubstantial to a person of ordinary skill in the relevant field.

Are There any Limitations on the Doctrine of Equivalents?

The most common limitation on the doctrine of the equivalents occurs when an inventor narrows the scope of his patent’s claims during the patent process in order to satisfy the elements of patentability. In this case, the inventor cannot later use the doctrine of equivalents to broaden the scope of the claims he had narrowed in order to get a patent. This limitation is called prosecution history estoppel.

Should I Hire a Patent Attorney?

If you believe you may have infringed upon someone’s patent or that someone has infringed upon your patent under the doctrine of equivalents, you should consult with a patent attorney. An experienced patent attorney can help you determine if any infringement has taken place, and can represent you in court if necessary.