Patent laws in the US have long allowed inventors to claim their invention using “means-plus-function” language. But, for the last two-decades or so it has generally been a bad idea to do so.
Means-plus-function language allows you to describe your invention using functional language: “a means for lifting a bar” or “a means for receiving a phone call.” If an inventor uses this language she is limited in what the claims cover to any corresponding structures in the disclosure of your patent. If she is claiming the means for lifting a bar, and only discloses a lever as a means for doing so in the patent – she is limited to just covering a lever – instead of any means for lifting a bar.
The Patent Office’s own guidance on this matter states:
[T]he broadest reasonable interpretation of a claim limitation that invokes [means-plus-function] is the structure, material or act described in the specification as performing the entire claimed function and equivalents to the disclosed structure, material or act. As a result [these] . . . limitations will, in some cases, be afforded a more narrow interpretation than a limitation that is not crafted in “means plus function” format.
In addition to potentially being more narrow than claims drafted with alternative language, Federal district courts regularly find patents using means-plus-function language invalid.
In a recent opinion, the Federal Circuit held that the phrases “program loading device” and “program recognition device” in the absence of explicit “means-plus-function” language still invoked this provision of patent law, and held the patent invalid as indefinite for failing to disclose a structure associated with the described functionality.
While this holding isn’t novel, it’s worrisome in that it further closes the gap between claims simply using functional language and “means-plus-function” claims. It is sometimes difficult to claim software without describing the functionality of that software. If describing the functionality, as the inventor did here, can trigger means-plus-function analysis, it opens another unpredictable avenue to invalidating software patents.