What are the criteria for determining whether functional language in a claim is definite?

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 criteria for determining whether functional language in a claim is definite include:

• Whether the claim scope is clear to a person of ordinary skill in the art
• Whether the specification provides a reasonable degree of clarity and particularity to inform skilled artisans of the claim scope
• Whether the claim language provides a clear-cut indication of the scope of subject matter covered by the claim

As stated in MPEP 2173.05(g): “The use of functional language in a claim may fail ‘to provide a clear-cut indication of the scope of the subject matter embraced by the claim’ and thus be indefinite.” However, functional language is not inherently indefinite. The key is to ensure that the language is sufficiently clear and supported by the specification.