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On Thursday, June 9, 2011, the Supreme Court issued its opinion in the landmark case Microsoft v. i4i Ltd. P’ship, upholding nearly 30 years of Federal Circuit precedent requiring a challenger to the validity of a patent to prove its case by clear and convincing evidence.

In its appeal over the prevailing evidentiary standard applied to invalidity challenges brought under 35 U.S.C. § 282, Microsoft presented two concurrent arguments. First, Microsoft argued that a preponderance standard should be applied to all patent invalidity challenges. In the alternative, Microsoft argued that, at least with respect to prior art that was never presented to the PTO or considered by an examiner, the existing clear and convincing standard should not apply. Specifically, Microsoft argued that the standard of proof for proving invalidity should be lowered to a preponderance when the prior art relied upon was never reviewed by the examiner during prosecution of the patent.

Section 282 provides that “[a] patent shall be presumed valid” and “[t]he burden of establishing invalidity of a patent or any claim thereof shall rest on the party asserting such invalidity.” In its opinion, the Supreme Court noted that, “while the statute explicitly specifies the burden of proof, it includes no express articulation of the standard of proof.” However, the Supreme Court went on to say that “by stating that a patent is ‘presumed valid,’ Congress used a term with a settled meaning in the common law.” That is, by the time Congress drafted Section 282, there was a universal understanding that a presumption of validity is “a presumption not to be overthrown except by clear and cogent evidence.” As a result, the Supreme Court refused to eliminate the common law understanding of the presumption of validity merely because Congress failed to expressly reiterate it when it drafted Section 282.

As to Microsoft’s second argument, i.e., that a lower standard should apply in cases that involve prior art never presented to the PTO, the Supreme Court resisted Microsoft’s urging to “enact a standard of proof that would rise and fall with the facts of each case.” Instead, the Supreme Court applied the “same commonsense principle that the Federal Circuit has recognized through its existence — namely, that new evidence supporting an invalidity defense may ‘carry more weight’ in an infringement action than evidence previously considered by the PTO,” but the standard of proof shall remain the same — clear and convincing.