Patents

Believing a Patent Is Invalid Is No Defense: Commil USA v. Cisco Systems

The Supreme Court held that a good-faith belief in a patent's invalidity does not negate the intent required for induced infringement, while reaffirming that inducement demands knowledge of infringement.

September 22, 2025
Wireless networking access point and equipment in an office ceiling
Commil's patent claimed a method for short-range wireless networks, and it accused Cisco of inducing customers to use infringing equipment. Shutterstock
Educational content, not legal advice. This article explains general legal concepts. It does not create an attorney–client relationship. For your specific situation, consult a licensed attorney.

In Commil USA, LLC v. Cisco Systems, Inc., No. 13-896 (U.S. May 26, 2015), the Supreme Court answered a question that sits at the intersection of two patent doctrines that courts usually keep apart: infringement and validity. Can a defendant defeat a claim of induced infringement by showing it sincerely believed the asserted patent was invalid? Writing for the majority, Justice Kennedy held that it cannot. A good-faith belief in invalidity is not a defense to inducement under 35 U.S.C. § 271(b), because infringement and validity are distinct issues. At the same time, the Court reaffirmed—drawing directly on its earlier Global-Tech decision—that inducement requires knowledge that the induced acts constitute patent infringement. The decision sharpened the mental-state element of inducement while closing a defense that had threatened to blur the line between the two doctrines.

At a glance

  • Court and date: Supreme Court of the United States, decided May 26, 2015; docket No. 13-896. Justice Kennedy delivered the majority opinion; the Court vacated and remanded the Federal Circuit’s judgment.
  • Patent: Commil holds a patent on a method of implementing short-range wireless networks, such as those used to hand off devices between access points.
  • The claims: Commil alleged that Cisco directly infringed by making and using networking equipment, and that Cisco induced infringement by selling the equipment to customers who then practiced the patented method.
  • The defense at issue: Cisco argued that its good-faith belief that Commil’s patent was invalid should negate the intent required for inducement.
  • Holding: A good-faith belief in a patent’s invalidity is not a defense to induced infringement. Separately, the Court reaffirmed that induced infringement requires the defendant to know that the induced acts constitute infringement of the patent.

Two questions, two doctrines

The case forced the Court to be precise about what an inducer must know. Section 271(b) imposes liability on whoever “actively induces infringement of a patent,” but the statute does not spell out the requisite mental state. In Global-Tech Appliances, Inc. v. SEB S.A., the Court had held that inducement requires knowledge that the induced acts constitute patent infringement—a standard satisfied either by actual knowledge or by willful blindness. Commil presented the natural follow-on question: if the relevant knowledge is knowledge of infringement, does a defendant’s belief that the patent is invalid negate that knowledge?

The intuition behind Cisco’s argument was not frivolous. One cannot infringe an invalid patent, the reasoning runs, so a defendant who genuinely believes the patent is invalid believes it is not causing infringement—and therefore lacks the intent inducement requires. The Court rejected the syllogism by insisting on the conceptual separation of the two doctrines.

Why belief in invalidity does not negate intent

The majority’s central move was to treat infringement and validity as legally independent inquiries. Infringement asks whether the accused conduct falls within the scope of the patent’s claims. Validity asks whether the patent should have issued at all. The Patent Act addresses them separately: § 271 governs infringement, while §§ 282 and 102–103 govern validity, and § 282 supplies a statutory presumption that an issued patent is valid. Because the doctrines are distinct, the Court reasoned, knowledge bearing on one does not substitute for knowledge bearing on the other. A defendant who knows it is inducing the performance of acts that fall within the claims has the knowledge § 271(b) requires, regardless of its private view about whether those claims will ultimately survive a validity challenge.

The Court reinforced the conclusion with practical concerns. Allowing a good-faith-invalidity defense would undermine the § 282 presumption of validity by letting an accused inducer effectively relitigate validity through the back door of intent. It would also burden trials, inviting juries to assess the sincerity and reasonableness of a defendant’s belief about a legal conclusion. And it was unnecessary as a matter of policy: a defendant who believes a patent is invalid has ample, well-established avenues to act on that belief—filing a declaratory-judgment action, seeking inter partes review or other Patent Office proceedings, or simply raising invalidity as a defense in the infringement suit itself. Invalidity, in other words, remains a complete defense to liability; it is just not a defense to the intent element of inducement.

Reaffirming the knowledge requirement

If part of Commil narrowed defendants’ options, another part confirmed a meaningful protection for them. The Court took the occasion to restate, and arguably underscore, the holding of Global-Tech: liability for induced infringement requires proof that the defendant knew that the induced acts constituted patent infringement. It is not enough to show the defendant knew of the patent’s existence or merely intended to bring about the underlying acts; the defendant must have known those acts infringed. This portion of the opinion corrected language in the Federal Circuit’s decision that could have been read to permit liability on a lesser showing, and it keeps the inducement standard demanding on the question that does matter—knowledge of infringement.

The Court closed with a notable aside aimed at abusive litigation. Recognizing the burdens that meritless patent suits impose, the majority reminded district courts of their tools to deter frivolous cases, including the discretionary power to award attorney’s fees in exceptional cases. The remark signaled that the answer to bad-faith patent assertion lies in case-management and fee-shifting authority, not in carving validity-based defenses into the intent element of inducement.

Open questions

Commil draws a clean line between infringement and validity, but the boundary it polices invites continued contest. The decision leaves room to debate how willful blindness operates in practice: what quantum of deliberate avoidance establishes the requisite knowledge of infringement, and how does that interact with opinions of counsel that address infringement rather than validity? The opinion also leaves the policing of abusive suits to the discretionary fee-shifting standard, the contours of which the Court was simultaneously reshaping in other cases—so the practical deterrent the majority invoked depends on how robustly trial courts wield it. Finally, although the Court foreclosed a good-faith-invalidity defense, a genuine and reasonable belief of non-infringement remains relevant to intent, and the line between the two beliefs can blur in practice.

Implications

  • Invalidity belief is no shield against inducement. A defendant cannot escape § 271(b) liability by arguing it thought the patent was invalid; that belief does not negate the intent inducement requires.
  • Knowledge of infringement is still essential. Inducement demands proof the defendant knew the induced acts infringed—not merely knowledge of the patent—preserving a real mental-state hurdle for plaintiffs.
  • Challenge validity through the proper channels. Accused inducers should pursue declaratory judgment, inter partes review, or an invalidity defense rather than rely on subjective belief.
  • Non-infringement opinions retain value. A reasoned belief of non-infringement still bears on intent, so well-supported opinions of counsel addressed to infringement remain a meaningful risk-management tool.
  • Fee-shifting, not intent doctrine, polices abuse. The Court pointed to attorney’s-fee awards in exceptional cases as the remedy for meritless suits, leaving inducement’s elements intact.

Frequently asked questions

Can a defendant avoid induced-infringement liability by believing the patent is invalid? No. The Supreme Court held that a good-faith belief in a patent’s invalidity is not a defense to induced infringement. Infringement and validity are separate issues, so a belief about validity does not negate the knowledge of infringement that § 271(b) requires. Invalidity itself remains a defense to liability—just not to the intent element of inducement.

What level of knowledge does induced infringement require? Following Global-Tech, the Court reaffirmed that the defendant must have known that the induced acts constituted patent infringement. Knowledge of the patent alone is insufficient; willful blindness can satisfy the standard, but mere intent to cause the underlying acts cannot.

How should a company act on a belief that a patent is invalid? Through established procedures rather than self-help: filing a declaratory-judgment action, petitioning for inter partes review or other Patent Office proceedings, or asserting invalidity as a defense in the infringement litigation. The Court emphasized these avenues in declining to recognize a belief-based defense.

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