Microsoft Corp. v. i4i Ltd. Partnership
The Supreme Court ruled that companies challenging a patent's validity in an infringement lawsuit must prove invalidity with clear and convincing evidence, not merely a preponderance of the evidence, rejecting Microsoft's bid for a lower bar.
The decision preserves a demanding evidentiary standard that has shaped patent litigation for decades, making it harder for accused infringers like Microsoft to knock out a patent even when the challenged evidence was never seen by the patent office.
“[O]ne otherwise an infringer who assails the validity of a patent fair upon its face bears a heavy burden of persuasion, and fails unless his evidence has more than a dubious preponderance.”
Quoting the Court's 1934 RCA decision to explain the historical meaning of the presumption of patent validity.
How it got here: A jury found Microsoft failed to prove invalidity under a clear-and-convincing standard; the trial court and the Federal Circuit both upheld that instruction, and Microsoft asked the Supreme Court to lower the standard.
The Case in Depth
What happened
i4i, which owned a patent covering a method for editing computer documents, sued Microsoft for willfully infringing that patent through certain Word products. Microsoft denied infringement and argued the patent was invalid because i4i had sold a similar software program, S4, more than a year before applying for the patent — a fact the parties agreed on, though they disputed whether S4 actually contained the patented invention.
The question before the Court
When a company accused of patent infringement claims the patent is invalid, does it have to prove that with strong, clear evidence, or just show it's more likely true than not?
The Court's answer
No — the Court held that a company challenging a patent's validity in an infringement lawsuit must prove invalidity with clear and convincing evidence, the same demanding standard courts had long used, not merely a preponderance of the evidence. The Court reasoned that when Congress wrote in 1952 that patents are "presumed valid," it used a term that already had a settled meaning in judge-made law requiring this heightened proof, and nothing in the statute's text suggested Congress meant something different.
The Court also rejected Microsoft's fallback argument that the standard should drop to a preponderance of the evidence whenever the challenger's evidence was never reviewed by the Patent Office. Congress set one uniform standard, not one that shifts with the facts of each case, though juries may still be told to weigh unreviewed evidence as potentially more persuasive.
Curious how the Court got there? See the step-by-step legal reasoning →
Why it matters
Businesses accused of infringing a patent will continue facing a steep evidentiary hurdle to prove the patent invalid, even when they present evidence the Patent Office never reviewed. Patent holders retain strong protection for their patents in court, while companies seeking cheaper or easier ways to challenge weak patents must look to Congress, not the courts, for any change.
What changes now
The Federal Circuit's judgment affirming the jury verdict against Microsoft stands, and the clear-and-convincing-evidence standard remains the law nationwide for patent invalidity defenses. The Court noted Congress has repeatedly amended patent law without lowering this standard, and left any future recalibration to Congress rather than the courts. This is a final decision resolving the legal question presented.
What this does not decide
The Court did not decide the case only applies when the challenger's evidence wasn't put before the patent examiner; it applies the same clear-and-convincing standard across the board. It also left open exactly how juries should be instructed about weighing new evidence the Patent Office never considered.
Concurrences and dissents
Concurrence — Justice Breyer
Justice Breyer joined the majority in full but wrote to stress that the clear-and-convincing standard applies only to factual disputes, not to legal questions about how the law applies to given facts. He suggested courts use jury instructions or special verdict forms to separate factual findings (subject to the heightened standard) from legal conclusions (not subject to it), so the demanding standard doesn't improperly protect patents on purely legal grounds.
Concurrence — Justice Thomas
Justice Thomas agreed with the outcome but disagreed with the majority's reasoning. He argued the phrase 'presumed valid' was not clearly established as a term of art carrying a specific standard of proof in 1952, since courts at the time disagreed about the presumption's force. Instead, he reasoned that because the statute is silent on the standard of proof, it simply left the pre-existing common-law clear-and-convincing standard from RCA undisturbed.
How the Court got there
The legal reasoning, step by step
- The Court applied the principle that when Congress writes a legal term into a statute that already had a settled meaning in judge-made law, courts assume Congress meant to adopt that established meaning unless the statute says otherwise.
- The patent statute at issue says a patent 'shall be presumed valid,' and the Court found that by 1952, when Congress wrote that language, courts already understood 'presumed valid' to require challengers to prove invalidity by clear and convincing evidence, not just a slight edge in the evidence.
- The Court rejected Microsoft's argument that this reading makes another part of the same sentence unnecessary, explaining that some redundancy in a statute doesn't defeat an otherwise sound reading, especially since Microsoft's own proposed readings had the same problem.
- The Court also rejected a fallback argument that the standard should drop to a preponderance of the evidence when the challenger's evidence was never seen by the Patent Office during examination, reasoning that Congress fixed one uniform standard rather than a standard that would shift case by case.
- The Court concluded that juries can still be instructed to weigh new evidence the Patent Office never saw as potentially more significant, but that this affects how convincing the evidence is, not the legal standard of proof itself.
Doctrinal impact
Cases affected by this decision
Reaffirms Radio Corp. of America v. Radio Engineering Laboratories, Inc. (293 U.S. 1)
The Court relied on this 1934 decision as establishing the clear-and-convincing standard that Congress codified in 1952.