Proof needed to invalidate patents
Microsoft v. i4i Limited Partnership
In brief
The Supreme Court upheld the Federal Circuit's ruling: a party arguing that a patent is invalid must prove it with clear and convincing evidence.
- Where it stands
- Decided
Decided 8-0 · June 9, 2011 · Opinion by Justice Breyer
- What it’s about
- i4i sued Microsoft, claiming a custom XML editor in some versions of Word infringed its patent; Microsoft argued that the patent was invalid.
- Who it affects
- Anyone arguing in court that a patent is invalid must provide clear and convincing evidence—strong, highly persuasive proof.
Summary: written with AI from the case record.
What it's about
The Supreme Court agreed with the lower court that a party challenging a patent must prove it invalid with clear and convincing evidence—strong, highly persuasive proof.
Section 282 of the Patent Act says patents are presumed valid.
Question presented
Must a challenge to a patent's validity offer clear and convincing evidence as proof?
What the Court decided
Holding
Section 282 requires an invalidity defense to be proved by clear and convincing evidence. 598 F. 3d 831, affirmed.
- Result
- Affirmed
The Court's reasoning
The Court read Section 282 of the Patent Act to require clear and convincing proof for a defense arguing that a patent is invalid.
The vote
- Joined the judgment
- Concurred in a separate opinion
- Wrote an opinion
- Majority · 7joined the Court's opinion
- Concurring · 1agreed with the result, wrote separately
- Thomaswrote separately
What's next
The Federal Circuit's ruling remains in place, and lower courts must apply the clear-and-convincing standard to patent-invalidity defenses.
Each side's argument
- i4i Limited Partnership
- i4i claimed that a custom XML editor in some versions of Microsoft Word infringed its patent.
- Microsoft Corporation
- Microsoft argued that i4i's patent was invalid.
Documents
Opinions
Audio
Docket activity
New analysis added
AI analysis generated: Case Briefing
New analysis added
AI analysis generated: Impact Analysis
AI analysis generated: Opinion Summary
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AI analysis generated: Decision Record
Case data updated: summary, question_presented, generation_metadata
Case data updated: question_presented, extraction_metadata
Audio Recording added: Oral Arguments - Microsoft Corporation v. i4i Limited Partnership
Opinion added: i4i Ltd
More questions
- Why did Justice Thomas agree only with the result?
- He said the Patent Act's statement that a patent is presumed valid did not clearly establish a specific proof standard.
- What limit did Justice Breyer identify?
- He said the clear-and-convincing standard applies to factual disputes, not legal questions about how the law applies to agreed facts.
Sources
Primary materials plus reporting. Best-effort analysis: this explainer relies on a mix of primary materials and trusted secondary sources. Official filings and opinions remain authoritative.