In Nautilus v. BioSig (Sup. Ct. 2014), the Supreme Court of the United States has just unanimously changed the Federal Circuit's long-standing test for how much ambiguity or vagueness a patent claim can have and still be valid.  

The "old" test for definiteness, created by the Court of Appeals for the Federal Circuit, states that a patent claim is only indefinite when it is not "amenable to construction" or "insolubly ambiguous." Datamize, LLC v. Plumtree Software, Inc., 417 F.3d 891, 898 (Fed. Cir. 2005).

In Nautilus, the Supreme Court ruled that the "insolubly ambiguous" or "amenable to construction" formulations "lack the precision § 112, ¶2 demands," referring to patent statute 35 U.S.C. § 112, ¶2 (patents must "conclude with one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention."). The Court stated further that "[t]o tolerate imprecision just short of that rendering a claim 'insolubly ambiguous' would diminish the definiteness requirement's public-notice function and foster the innovation discouraging 'zone of uncertainty.'" Quoting United Carbon Co. v. Binney & Smith Co ., 317 U. S. 228, 236 (1942).

As an illustration of the ambiguity that is possible even for "definite" claims under the old test, Nautilus' petition states that Biosig's patent claims had been construed three different ways by four different judges. There is little doubt that even where claims can have multiple "reasonable" constructions, they have often been found to be sufficiently definite to satisfy § 112, ¶2.

The Supreme Court's decision leaves unchanged two factors in determining whether patent claims are indefinite. First, the standard is applied from the point of view of "those skilled in the art." Second, the inquiry is focused on what a claim's meaning would be understood to be at the time of the patent application. The new test announced is that 35 U.S.C. § 112, ¶2 requires "that a patent's claims, viewed in light of the specification and prosecution history, inform those skilled in the art about the scope of the invention with reasonable certainty. The definiteness requirement, so understood, mandates clarity, while recognizing that absolute precision is unattainable."

Conclusion

It remains to be seen how much of an impact this decision will have on patent cases, but at a minimum, replacing the nearly impossible-to-meet "insolubly ambiguous" standard with the new test should better serve the function of putting the public on notice of what is, and what is not, covered by a patent claim.