Means-Plus-Function Claim

A claim, which contains elements written in terms of “means for,” and identifying a function, or in a method claim the conjunction “steps-for” and describing a effect, purpose or outcome. In U.S. patent law such language is permissible under 35 U.S.C. §112, but such claims are “construed to cover the corresponding structure, material, or acts described in the specification and equivalents thereof,” i.e., they are usually limited to the means or steps described in the specification employed for the same function and limited equivalents. The same restricted construction does not exist in other jurisdictions so it is important to review and strip out “means-for” language in claims when transferring non-US patent filings into the US.

Under US patent law when the claim language has the conjunctions “means for” and “steps for” it is presumed to be means-plus-function or steps-plus-function – and formerly, there was a strong presumption that not using either conjunction means the claim is not means-plus-function or steps-plus-function.  However, in 2015, the Federal Circuit, troubled by the frequency with which purely functional claims were being filed on computer and software inventions, changed this presumption in an en-banc Federal Circuit Court of Appeals decision in Williamson v. Citrix Online, LLC. The effect of Williamson is that the presumption a claim is not means-plus function (or steps-plus-function) can be overcome if a:

challenger demonstrates that the claim term fails to ‘recite sufficiently definite structure’ or else recites ‘function without reciting sufficient structure for performing that function.

The effect of Williamson has been to severely curtail the scope of a large number of patents filed before 2015 when patent attorneys believed that functional language without those conjunctions was not limiting.

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