The Supreme Court ruled last week in Microsoft Corporation v. i4i Limited Partnership that “clear and convincing evidence” is still the standard of proof required to invalidate a patent. Section 282 of the Patent Act states that “a patent shall be presumed valid” and that “[t]he burden of establishing invalidity of a patent or any claim thereof shall rest on the party asserting such invalidity.” The Court relied on its own precedent to validate the Federal Circuit’s consistent application of the clear and convincing standard of proof to support an invalidity defense.

Defendant Microsoft asserted in this case that i4i’s allegedly infringed patent was rendered invalid as a result of i4i’s prior sale of software more than one year before its filing date. Importantly, this particular piece of software was never presented to the PTO examiner who issued the patent. Microsoft argued that since the PTO never actually looked at this prior art, the presumption of the patent’s validity would be weakened. Therefore, it argued that the standard of proof with respect to this sort of prior art should be a mere preponderance of the evidence, as opposed to the more difficult-to-achieve “clear and convincing” standard.

The Supreme Court rejected this argument and kept the clear and convincing standard in place. The Court relied on the fact that the Patent Act was drafted against the backdrop of earlier Supreme Court interpretations applying a close relative of the clear and convincing standard. Congress’s use of the term “presumed valid” thus codified the Court’s application of the presumption, absent evidence to the contrary. The majority opinion also cited legislative history of the Patent Act that supported this position. As to prior art that was never presented to the PTO, the Court held that the best way to account for the potentially weakened presumption of validity in these cases would be to instruct the jury to consider the fact that the PTO did not examine that prior art. Although Microsoft and various amici proposed policy arguments against imposing such a high hurdle to prove invalidity, the Court determined that - given Congress’s apparent acceptance of the way courts have applied the presumption over the last half-century - it was in no position to weigh the soundness of those policy arguments.

This potentially significant case ultimately resulted in no significant change to the law. It simply makes clear that an accused infringer asserting invalidity must present clear and convincing evidence to successfully support its position.