The U.S. Supreme Court held that a defendant accused of patent infringement must prove invalidity by the standard of clear and convincing evidence, rejecting Microsoft’s argument that a lower standard of proof, such as "preponderance of the evidence," could suffice. The ruling may still be beneficial to defendants, however, as the court acknowledged that "new" prior art should be given greater weight in the invalidity analysis than prior art previously considered by the U.S. Patent and Trademark Office (USPTO).

In the United States, a patent is presumed valid. Thus, a party asserting invalidity of a patent bears the burden of proof. The U.S. Patent Act does not articulate the applicable standard for proving invalidity, but lower courts (and in particular the Federal Circuit) have interpreted it as requiring “clear and convincing evidence.” In the case at bar, Microsoft had nonetheless argued that it need not prove invalidity by clear and convincing evidence — rather, a lower standard of a preponderance of the evidence should suffice, at least where the prior art had not been considered by the USPTO.

The Supreme Court unequivocally rejected Microsoft’s argument, ruling that the Patent Act requires that invalidity be proved by clear and convincing evidence. The court made this determination by looking to the history of invalidity and 35 U.S.C. § 282 (the relevant section of the Patent Act). The court found that while § 282 did not expressly articulate a standard of proof, Congress had intended to codify existing common law with its enactment. And this existing common law carried with it a heightened standard of proof — specifically, validity was "not to be overthrown except by clear and cogent evidence."

Looking forward, despite the fact that the court affirmed the higher standard of proof, the court's decision may nonetheless prove to be beneficial to defendants, as the court expressly acknowledged that "new" prior art might be given greater weight than prior art previously considered by the USPTO. Indeed, the court suggested that "new" prior art may make it easier to sustain a showing of clear and convincing evidence of invalidity.

The court also suggested that the additional weight that may be afforded "new" prior art can be addressed through jury instructions and verdict forms. Indeed, one of the more interesting — and perhaps beneficial — aspects of the court's decision is that it arguably sanctions jury instructions that

(1) inform jurors that certain prior art was not considered by the USPTO and

(2) instruct the jurors to consider this fact in determining whether invalidity has been proved by clear and convincing evidence.

This should make it easier for defendants to obtain jury instructions such as these, particularly in jurisdictions that do not routinely permit them.

One other notable aspect of the court's decision is Justice Breyer's concurrence, wherein he emphasized that the clearand- convincing standard applies only to questions of fact. This is particularly relevant in the patent context, since obviousness, although it depends on factual inquiries, is ultimately a question of law. Justice Breyer suggested that, by properly confining the heightened clear-and-convincing standard to factual inquiries, "courts can increase the likelihood that discoveries or inventions will not receive legal protection where none is due." Similar to the majority, he suggested that jury instructions and verdict forms can be used to separate out "factual and legal aspects of an invalidity claim."