What is the “Mere Function of Machine” rule 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 “Mere Function of Machine” rule refers to a principle in patent law that protects process or method claims from being rejected solely based on their relationship to a disclosed machine or apparatus. According to MPEP 2173.05(v):

“Process or method claims are not subject to rejection by U.S. Patent and Trademark Office examiners under 35 U.S.C. 112(b) or pre-AIA 35 U.S.C. 112, second paragraph, solely on the ground that they define the inherent function of a disclosed machine or apparatus.”

This rule ensures that otherwise patentable process claims are not rejected simply because they describe steps that a disclosed apparatus would inherently perform.