In Microsoft Corp. v. i4i Ltd. Partnership, 131 S. Ct. 2238 (2011), the Supreme Court held that Section 282 of the Patent Act, which provides that “[a] patent shall be presumed valid,” requires that an invalidity defense be proven by clear and convincing evidence, even if the defense rests on evidence never considered by the PTO during the examination process.

Having failed at trial to prove patent invalidity under the contested clear and convincing standard, Microsoft argued that an infringement defendant need only prove invalidity by a preponderance of the evidence. In the alternative, Microsoft argued that a preponderance standard must at least apply if an invalidity defense is based on evidence that was not before the PTO, and questioned why deference should be given to the PTO with respect to evidence the PTO never considered.

The Supreme Court affirmed the Federal Circuit’s opinion, holding that clear and convincing evidence is the correct standard. The Court acknowledged that Section 282 does not expressly articulate a standard of proof, but concluded that because Judge Cardozo’s 1934 opinion in RCA adopted a clear and convincing standard, the Patent Act, enacted in 1952, implicitly incorporated that standard through the use of the phrase “presumed valid,” which had a settled common law meaning.

The Court also rejected Microsoft’s alternative argument, concluding that Congress would have made it expressly clear if Congress had intended that a lower standard be applied to evidence that was not before the PTO. The Court did, however, recognize that (i) a jury could consider that the PTO had no opportunity to evaluate specific evidence, (ii) such evidence could be weighed more heavily, and (iii) the party asserting invalidity might therefore more easily satisfy its burden under the clear and convincing evidence standard.