Patent Law FAQ

Means-plus-function claim limitations have a special relationship with the written description requirement. According to MPEP 2163.03:

“A claim limitation expressed in means- (or step-) plus-function language ‘shall be construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof.’ 35 U.S.C. 112(f) or pre-AIA 35 U.S.C. 112, sixth paragraph.”

However, if the specification doesn’t provide sufficient corresponding structure, materials, or acts that perform the entire claimed function, two issues arise:

1. The claim becomes indefinite under 35 U.S.C. 112(b) because the applicant hasn’t particularly pointed out and distinctly claimed the invention.
2. The claim lacks adequate written description under 35 U.S.C. 112(a).

The MPEP explains:

“Such a limitation also lacks an adequate written description as required by 35 U.S.C. 112(a) or pre-AIA 35 U.S.C. 112, first paragraph, because an indefinite, unbounded functional limitation would cover all ways of performing a function and indicate that the inventor has not provided sufficient disclosure to show possession of the invention.”

Therefore, when using means-plus-function limitations, it’s crucial to provide clear and sufficient description of the corresponding structure in the specification to satisfy both the definiteness and written description requirements.

To learn more:

• means-plus-function
• written description
• 35 U.S.C. 112(f)
• indefiniteness
• functional limitations