How does the MPEP address the use of “substantially” in patent claims?

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 MPEP addresses the use of “substantially” in patent claims in MPEP 2173.05(b). The term is often used to mean “the same as if fully met,” as in “substantially horizontal.” The MPEP states:

“The term ‘substantially’ is often used in conjunction with another term to describe a particular characteristic of the claimed invention. It is a broad term. In re Nehrenberg, 280 F.2d 161, 126 USPQ 383 (CCPA 1960).”

However, the acceptability of the term depends on whether it can be interpreted by a person of ordinary skill in the art with reasonable certainty. If the term’s meaning is reasonably ascertainable in the context of the invention, it may be acceptable. Otherwise, it could render the claim indefinite.