What is the “reasonable expectation of success” requirement in patent law?

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.

The “reasonable expectation of success” requirement is a crucial element in determining obviousness in patent law. According to MPEP 2143.02, “Where there is a reason to modify or combine the prior art to achieve the claimed invention, the claims may be rejected as prima facie obvious provided there is also a reasonable expectation of success.”

This means that when combining or modifying prior art references to arrive at a claimed invention, there must be a reasonable expectation that the combination or modification would work as intended. The standard does not require absolute certainty, but rather a reasonable likelihood of success based on the knowledge available at the relevant time.