What rejections should be considered for unsupported means-plus-function limitations?

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.

When a means- (or step-) plus-function limitation in a claim is not supported by corresponding structure, material, or acts in the specification, the examiner should consider the following rejections under 35 U.S.C. 112:

• Enablement (35 U.S.C. 112(a)): If the skilled artisan would not know how to make and use the invention without a description of elements to perform the function.
• Written Description (35 U.S.C. 112(a)): If the specification does not describe the claimed invention in sufficient detail to demonstrate possession of the claimed invention.
• Indefiniteness (35 U.S.C. 112(b)): As being unclear or ambiguous due to lack of corresponding structure.

The MPEP provides specific guidance for computer-implemented means-plus-function limitations:

“If the means- (or step-) plus-function limitation is computer-implemented, and the specification does not provide a disclosure of the computer and algorithm in sufficient detail to demonstrate to one of ordinary skill in the art that the inventor possessed the invention, see MPEP § 2161.01 and MPEP § 2181, subsection IV, a rejection under 35 U.S.C. 112(a) or pre-AIA 35 U.S.C. 112, first paragraph, for lack of written description must be made.”