Today, in Williamson v. Citrix, the Federal Circuit overruled its ill-advised case law that has been one of the primary drivers of overbroad software patents. The court finally recognized that patent applicants cannot bypass certain limits on patent rights solely by avoiding magic words. EFF filed an amicus brief urging the court to do just that.

Imagine the Wright brothers, after they invented their airplane, filed for a patent claiming “a machine for flying.” Essentially claiming a machine for what it does rather than how it does it. This is known as “functional claiming.”

Under previous Federal Circuit precedent, there was a very strong presumption that would give the Wright brothers the rights to any “machine for flying,” including things like the rocket or the Space Shuttle. But the Wright brothers only invented one type of machine for flying: why would they get to own things they didn’t invent?

The U.S. Supreme Court, in the early 20th century, saw the danger of these types of “functionally” defined inventions. As it explained in the seminal 1946 case Halliburton v. Walker:

In this age of technological development there may be many other devices beyond our present information or indeed our imagination which will perform that function and yet fit these claims. And unless frightened from the course of experimentation by broad functional claims like these, inventive genius may evolve many more devices to accomplish the same purpose.

In 1952, in what many commentators believe to be a response to Halliburton, Congress revised the Patent Act to allow functional claiming, but did so with an important caveat. That caveat allowed inventors to claim their inventions functionally, yet the scope of the patent rights would be limited to only what the inventor actually structurally described in the patent specification (or its equivalents). The Wright brothers could claim their “machine for flying,” limited to what they actually described and things that were essentially the same, but they couldn’t stop someone from building the Space Shuttle.

Unfortunately, the Federal Circuit interpreted the law extremely narrowly and made it far too easy for patent applicants to avoid it. Essentially, as long as a patent applicant avoided using the magic words (“means for”), the court would not apply the law that limited the claims to what was actually described. Under previous Federal Circuit law, since “machine” wasn’t one of the court’s magic words, the Wright brothers could claim to own the Space Shuttle.

Today, finally, the Federal Circuit overruled that case law and recognized the statute means what it says: if you claim something functionally, regardless of whether you use magic words, you’re likely limited to what you actually describe.

Restrictions on functional claiming will not solve all problems with software patents. But they will make it harder for applicants to come up with one way to solve a problem and then monopolize all ways of solving that problem, a tactic that is notoriously widespread with software patents. The court’s future decisions will hopefully apply Williamson to the types of claims used by most software patents. This decision has the potential to go a long way in ensuring that these claims are appropriately limited.