Microsoft Corp. v. i4i Ltd. Partnership, 564 U.S. 91

Under §282, a patent is presumed valid and the burden to prove invalidity rests on the party asserting it.
The issue is whether §282 requires a clear and convincing standard of proof for invalidity defenses in an infringement action.
The patent in suit concerns an improved method for editing documents; i4i asserted the patent's validity while Microsoft challenged it.
The on-sale bar (§102(b)) was argued by Microsoft as a basis for invalidity, based on i4i's prior sale of S4 software.
The district court instructed the jury to apply the clear-and-convincing-evidence standard for invalidity; the Federal Circuit affirmed.
The Court held that Congress codified the common-law presumption of validity with a heightened standard of proof, i.e., clear and convincing evidence, to overcome §282.

Issue	Plaintiff's Argument	Defendant's Argument	Held
What standard of proof governs invalidity defenses under §282?	Microsoft argues for a preponderance standard or a variable standard.	i4i supports the clear-and-convincing standard codified by §282.	Clear and convincing standard governs invalidity defense.
Does the presumption of validity carry a heightened standard of proof regardless of evidence considered by the PTO?	Microsoft argues the presumption alone shifts only production burdens or allows a variable standard.	i4i argues the common-law meaning of presumption includes a heightened burden of proof.	The heightened standard applies; Congress preserved the common-law meaning.
Can a preponderance standard apply when evidence was not before the PTO during examination (e.g., new evidence)?	Microsoft contends a preponderance standard should apply when PTO didn’t consider the evidence.	i4i argues for a uniform strict standard, with weight given to new evidence as appropriate under clear and convincing standard.	No, standard remains clear and convincing; evidence not before PTO may be weighed but does not lower the standard.

Radio Corp. of America v. Radio Engineering Laboratories, Inc., 293 U. S. 1 (1934) (presumption of validity with heavy burden to overcome by clear and cogent evidence)
American Hoist & Derrick Co. v. Sowa & Sons, Inc., 725 F.2d 1350 (CA Fed. 1984) (established presumption of validity and clear-and-convincing standard for invalidity)
Graham v. John Deere Co. of Kansas City, 383 U. S. 1 (1966) (ultimate patent validity question is a question of law with underlying factual inquiries)
Pfaff v. Wells Electronics, Inc., 525 U. S. 55 (1998) (on-sale bar and prior art considerations discussed in invalidity context)
Neder v. United States, 527 U. S. 1 (1999) (treats common-law terms with settled meanings and incorporation into statutes)