Background
Gary Williamson held a patent on a system for conducting distributed learning — essentially an online classroom or webinar platform that allowed a presenter and audience members to communicate and share content across computer systems. The patent claimed a “distributed learning control module” responsible for receiving and relaying communications between presenter and audience systems and coordinating streaming data. Williamson sued Citrix Online (the provider of GoToMeeting and related collaboration software) for patent infringement. The district court construed “distributed learning control module” as a means-plus-function limitation under 35 U.S.C. § 112 ¶ 6 — a clause of the patent statute that governs claims that describe an element by what it does (its function) rather than what it is (its structure). When § 112 ¶ 6 applies, the claim covers only the corresponding structure described in the specification. The district court then found the claim indefinite because the specification disclosed no corresponding structure for the control module’s functions. Summary judgment of invalidity followed.
On appeal, the en banc Federal Circuit confronted a long-standing rule that claims lacking the word “means” carry a “strong presumption” against means-plus-function treatment — a presumption that had led patent drafters to deliberately avoid “means” in favor of functionally equivalent nonce words like “module,” “component,” “unit,” “device,” and “mechanism” to avoid the structural disclosure requirements of § 112 ¶ 6.
The Court’s Holding
The en banc court overruled the “strong presumption” rule, holding that the heightened burden imposed by that rule was “unjustified” and had the improper effect of tilting the analysis in favor of not applying § 112 ¶ 6 even when claim language was purely functional. The new standard: the same test applies regardless of whether the word “means” appears. The question is simply whether the claim term fails to “recite sufficiently definite structure” or “recites function without reciting sufficient structure for performing that function.” If so, § 112 ¶ 6 applies.
Applying this standard, the court held that “distributed learning control module” was a means-plus-function limitation. The word “module” is a “nonce word” — a generic, structureless placeholder that can mean almost anything — and the surrounding claim language described only functions (receiving, relaying, coordinating) without conveying any structural information about how the module is built or organized. Because the specification likewise disclosed no specific algorithm or structure corresponding to the claimed functions, the court affirmed the finding of indefiniteness. Software claims that recite functions using nonce words without identifying the specific algorithm or hardware structure performing those functions are vulnerable to both § 112 ¶ 6 treatment and indefiniteness findings.
Key Takeaways
- The old “strong presumption” against means-plus-function treatment for claims lacking the word “means” is overruled — the analysis is now the same whether or not “means” appears.
- Generic nonce words like “module,” “component,” “unit,” “mechanism,” and “device” do not supply sufficient structure to avoid means-plus-function treatment when the claim uses them to perform a function without any structural content.
- When § 112 ¶ 6 applies to a software claim, the specification must disclose the specific algorithm (or structure) performing the claimed function — a general-purpose computer or processor alone is not sufficient corresponding structure for a software-implemented function.
- The decision triggered a wave of invalidity challenges to software patents that had deliberately avoided “means” language while claiming purely functional limitations, exposing many issued patents to § 112 ¶ 6 indefiniteness arguments.
Why It Matters
Williamson v. Citrix is one of the most practically consequential Federal Circuit decisions of the decade for software patent drafters. For years, practitioners had treated “means” as a dangerous word that triggered § 112 ¶ 6 and avoided it by substituting nonce words — a strategy that worked under the old strong-presumption framework. After Williamson, that strategy is no longer reliable. Using “module,” “unit,” or similar functional placeholders to perform a claimed function without providing structural content can trigger means-plus-function treatment just as surely as using “means.”
For new patent applications, the lesson is to either: (a) provide explicit structural language that describes how a component is built (hardware components, circuits, specific algorithms, data structures); or (b) accept means-plus-function treatment and ensure the specification contains detailed, clearly labeled corresponding structure for each function. For issued patents, the decision created substantial exposure for software patents in litigation — accused infringers began routinely arguing that functional claiming with nonce words triggers § 112 ¶ 6 and indefiniteness when the specification lacks algorithm disclosure. Understanding Williamson is now essential to both asserting and defending against software patent claims.