35 U.S.C. § 282: Presumption of Validity, Defenses, and Burden of Proof

Under 35 U.S.C. § 282, every claim of an issued U.S. patent is presumed valid, and anyone asserting invalidity or noninfringement carries the burden of proof. The statute sets a high evidentiary bar, lists the defenses a defendant may raise in an infringement suit, and requires 30 days’ written notice before trial of the prior art and witnesses a challenger intends to use.¹

The Presumption and Who Carries the Burden

Section 282(a) makes the presumption automatic on issuance. It attaches claim by claim, not to the patent as a single document. An independent claim, a dependent claim, and a multiple dependent claim each carry their own presumption, and a dependent claim stays presumed valid even if the broader claim it depends on is later invalidated.¹

The consequence for litigation is simple. The patent holder walks in owing no proof of validity. The entire burden sits with the challenger. That deference reflects the fact that a patent examiner already reviewed the application, searched prior art, and concluded the invention was patentable, and the law treats that administrative judgment as credible unless someone dislodges it. Utility, design, and plant patents all receive the same presumption.¹

The Clear and Convincing Evidence Standard

Most civil claims are decided by preponderance of the evidence: more likely true than not. Patent invalidity demands more. The challenger must produce clear and convincing evidence, showing it is highly probable the patent should never have issued.¹

The Supreme Court fixed this standard in Microsoft Corp. v. i4i Limited Partnership, holding that § 282 requires clear and convincing evidence for any invalidity defense, with no exceptions.² Microsoft had argued for a lower standard whenever the challenger relies on prior art the examiner never saw. The Court rejected that. Congress codified one standard, not one that rises or falls with the record.

The Court did acknowledge that the examiner’s exposure to the evidence matters at the margin. A jury can be told the Patent Office never considered the prior art now being presented, and it can weigh that fact when deciding whether the challenger has cleared the bar. The standard of proof does not shift, but the jury’s confidence in the original examination can.²

Defenses Available Under Section 282(b)

Section 282(b) fixes the menu of defenses a defendant may raise. The list falls into a few groups.

Noninfringement

The first listed defense is often the cleanest: the accused product or process simply does not fall within the scope of the asserted claims.¹ This defense concedes nothing about the patent’s validity; it disputes only that the defendant actually practiced the patented invention.

Invalidity Grounds

Section 282(b)(2) confines invalidity arguments to grounds identified elsewhere in the patent code as conditions for patentability, and § 282(b)(3) adds failures to meet §§ 112 and 251. In practice, four provisions drive most disputes.

Section 101 — subject matter and utility. Section 101 limits patents to new and useful processes, machines, manufactured articles, and compositions of matter. A challenger may argue the claim covers an abstract idea, a law of nature, or a natural phenomenon, none of which are patentable, or that the invention lacks any real-world practical use.³

Section 102 — novelty. A patent is only valid if the claimed invention was new when the applicant filed. Under § 102, the patent can fall if the invention was already described in another patent, published, in public use, on sale, or otherwise available to the public before the effective filing date.⁴ Challengers usually rely on prior patents or printed publications.

Section 103 — non-obviousness. Even when no single reference discloses the entire invention, the patent is invalid if the differences between the invention and the prior art would have been obvious to a person of ordinary skill in the field at the time of filing.⁵ The question is not whether the invention looks obvious in hindsight, but whether a skilled worker at the time would have found it a routine step from what was already known. Obviousness is where most validity fights are actually won or lost.

Section 112 — written description and enablement. The patent must describe the invention clearly enough for a skilled reader to make and use it without guessing or extensive experimentation.⁶ Section 112 still requires the inventor to disclose the best mode known for carrying out the invention, but the America Invents Act removed the courtroom consequence: failure to disclose best mode can no longer be used to cancel, invalidate, or render a claim unenforceable.¹

Unenforceability

Unenforceability is a separate defense, and its most common form is inequitable conduct. If the applicant deliberately withheld material information from the Patent Office or submitted misleading information during prosecution, a court can declare the patent unenforceable. Proving inequitable conduct requires clear and convincing evidence of both the materiality of what was withheld and a specific intent to deceive. The consequences reach beyond the patent in suit; a finding of inequitable conduct can render related patents in the same family unenforceable as well.

Prior Commercial Use and the Catchall

Section 282(b)(4) sweeps in “any other fact or act made a defense by this title.” The most substantial defense living under that clause is prior commercial use under § 273. A business that commercially used the patented subject matter in good faith at least one year before the patent’s effective filing date can continue that use despite the later patent. The party invoking the defense must prove it by clear and convincing evidence, and the defense is personal: it cannot be separately licensed or sold, only transferred with the entire business line to which it relates.⁷

The 30-Day Pretrial Notice Rule

Section 282(c) imposes a disclosure obligation that trips up unprepared challengers. At least 30 days before trial, a party planning to assert invalidity or noninfringement must give the patent holder written notice identifying the evidence it intends to use.¹

The notice must identify prior patents by country, number, date, and patentee name. For publications used to anticipate the claim or to show the state of the art, the notice must give the title, date, and page numbers. If the challenger will call witnesses to prior knowledge, prior use, or prior sale of the invention, the notice must identify those witnesses by name and address.¹

Skipping the notice has teeth. The statute states that without it, “proof of the said matters may not be made at the trial except on such terms as the court requires.”¹ Courts retain discretion to admit late evidence on conditions, but a challenger who misses the window may lose the ability to present its strongest prior art at the worst possible moment.

Challenges to Extended Patent Terms

Section 282(c) also gives a defendant a route to attack a patent’s extended term. Where a term has been extended under § 154(b) for Patent Office delays or under § 156 for products awaiting regulatory approval, and the extension was granted because of a material failure by the applicant or the Director to comply with those provisions, invalidity of the extension is a standalone defense in any infringement suit covering the extended period.¹ One carve-out: a due diligence determination made under § 156(d)(2) cannot be revisited in the infringement case.

Why the PTAB Is Different

Section 282’s clear and convincing standard governs federal district court litigation. It does not govern administrative challenges at the Patent Trial and Appeal Board. Inter partes review under § 311 and post-grant review under § 321 both allow the petitioner to prove unpatentability by a preponderance of the evidence.⁸⁹ IPR is limited to novelty and obviousness grounds based on patents or printed publications.¹⁰ PGR reaches any ground available as an invalidity defense under § 282(b)(2) or (b)(3), including subject matter eligibility and § 112 problems.¹¹

The gap between the two standards is not academic. Prior art that would fall short of clear and convincing in a district court may still carry the day at the Board under a preponderance standard. That is why accused infringers frequently file IPR petitions alongside district court litigation, and why the practical weight of § 282’s presumption depends heavily on which forum is deciding the question.

1
Office of the Law Revision Counsel. 35 USC 282 – Presumption of Validity; Defenses
2
Justia U.S. Supreme Court Center. Microsoft Corp. v. i4i Limited Partnership
3
Office of the Law Revision Counsel. 35 U.S. Code 101 – Inventions Patentable
4
Office of the Law Revision Counsel. 35 U.S. Code 102 – Conditions for Patentability; Novelty
5
Office of the Law Revision Counsel. 35 U.S. Code 103 – Conditions for Patentability; Non-Obvious Subject Matter
6
Office of the Law Revision Counsel. 35 U.S. Code 112 – Specification
7
Office of the Law Revision Counsel. 35 U.S. Code 273 – Defense to Infringement Based on Prior Commercial Use
8
Office of the Law Revision Counsel. 35 U.S. Code 316 – Conduct of Inter Partes Review
9
Office of the Law Revision Counsel. 35 U.S. Code 326 – Conduct of Post-Grant Review
10
Office of the Law Revision Counsel. 35 USC 311 – Inter Partes Review
11
Office of the Law Revision Counsel. 35 USC 321 – Post-Grant Review