What factors support a conclusion that a prior art element is an equivalent?

This page is an FAQ based on guidance from the Manual of Patent Examining Procedure. It is provided as guidance, with links to the ground truth sources. This is information only: it is not legal advice.

According to MPEP 2183, there are three main factors that support a conclusion that a prior art element is an equivalent:

1. Identical function and results: “The prior art element performs the identical function specified in the claim in substantially the same way, and produces substantially the same results as the corresponding element disclosed in the specification.“
2. Recognized interchangeability: “A person of ordinary skill in the art would have recognized the interchangeability of the element shown in the prior art for the corresponding element disclosed in the specification.“
3. Insubstantial differences: “There are insubstantial differences between the prior art element and the corresponding element disclosed in the specification.“

The examiner should demonstrate at least one of these factors to support a conclusion of equivalence.