, 
at ___
(slip op., at 10)). By stating that Cisco could be found
liable if it “ ‘knew or should have known that its actions
would induce actual infringement,’ ” the Court of Appeals
explained, the District Court had allowed “the jury to find
[Cisco] liable based on mere negligence where knowledge
is 
required.” 720 F.3d, at 1366
. That ruling, which re-
quires a new trial on the inducement claim with a corrected
instruction on knowledge, is not in question here.
   What is at issue is the second holding of the Court of
Appeals, addressing Cisco’s contention that the trial court
committed further error in excluding Cisco’s evidence that
it had a good-faith belief that Commil’s patent was in-
valid. Beginning with the observation that it is “axiomatic
that one cannot infringe an invalid patent,” the Court of
Appeals reasoned that “evidence of an accused inducer’s
good-faith belief of invalidity may negate the requisite
intent for induced infringement.” 
Id., at 1368. 
The court
saw “no principled distinction between a good-faith belief
of invalidity and a good-faith belief of non-infringement for
the purpose of whether a defendant possessed the specific
intent to induce infringement of a patent.” 
Ibid.
   Judge Newman dissented 
on that point. In Judge
Newman’s view a defendant’s good-faith belief in a pa-
tent’s invalidity is not a defense to induced infringement.
She reasoned that “whether there is infringement in fact
does not depend on the belief of the accused infringer that
it might succeed in invalidating the patent.” 
Id., at 1374
(opinion concurring in part and dissenting in part). Both
parties filed petitions for rehearing en banc, which were
                  Cite as: 575 U. S. ____ (2015)            5

                      Opinion of the Court

denied. 
737 F.3d 699
, 700 (2013). Five judges, however,
would have granted rehearing en banc to consider the
question whether a good-faith belief in invalidity is a
defense to induced infringement. 
Id., at 700 
(Reyna, J.,
dissenting from denial of rehearing en banc).
  This Court granted certiorari to decide that question.
574 U. S. ___ (2014).
                              II
  Although the precise issue to be addressed concerns a
claim of improper inducement to infringe, the discussion
to follow refers as well to direct infringement and contrib-
utory infringement, so it is instructive at the outset to set
forth the statutory provisions pertaining to these three
forms of liability. These three relevant provisions are
found in §271 of the Patent Act. 
35 U.S. C
. §271.
  Subsection (a) governs direct infringement and provides:
      “Except as otherwise provided in this title, whoever
    without authority makes, uses, offers to sell, or sells
    any patented invention, within the United States or
    imports into the United States any patented invention
    during the term of the patent therefor, infringes the
    patent.”
Under this form of liability, a defendant’s mental state is
irrelevant. Direct infringement is a strict-liability offense.
Global-Tech, 563 U. S., at ___ (slip op., at 5, n. 2).
   Subsection (b) governs induced infringement:
      “Whoever actively induces infringement of a patent
    shall be liable as an infringer.”
In contrast to direct infringement, liability for inducing
infringement attaches only if the defendant knew of the
patent and that “the induced acts constitute patent in-
fringement.” Id., at ___ (slip op., at 10). In Commil and
the Government’s view, not only is knowledge or belief in
6         COMMIL USA, LLC v. CISCO SYSTEMS, INC.

                     Opinion of the Court

the patent’s validity irrelevant, they further argue the
party charged with inducing infringement need not know
that the acts it induced would infringe. On this latter
point, they are incorrect, as will be explained below.
  Subsection (c) deals with contributory infringement:
       “Whoever offers to sell or sells within the United
    States or imports into the United States a component
    of a patented machine, manufacture, combination or
    composition, or a material or apparatus for use in
    practicing a patented process, constituting a material
    part of the invention, knowing the same to be espe-
    cially made or especially adapted for use in an in-
    fringement of such patent, and not a staple article or
    commodity of commerce suitable for substantial non-
    infringing use, shall be liable as a contributory
    infringer.”
Like induced infringement, contributory infringement
requires knowledge of the patent in suit and knowledge of
patent infringement. Aro Mfg. Co. v. Convertible Top
Replacement Co., 
377 U.S. 476
, 488 (1964) (Aro II).
  This case asks a question of first impression: whether
knowledge of, or belief in, a patent’s validity is required
for induced infringement under §271(b).
                             A
   Before turning to the question presented, it is necessary
to reaffirm what the Court held in Global-Tech. Commil
and the Government (which supports Commil in this case)
argue that Global-Tech should be read as holding that
only knowledge of the patent is required for induced in-
fringement. That, as will be explained, would contravene
Global-Tech’s explicit holding that liability for induced
infringement can only attach if the defendant knew of the
patent and knew as well that “the induced acts constitute
patent infringement.” 563 U. S., at ___ (slip op., at 10).
                 Cite as: 575 U. S. ____ (2015)            7

                     Opinion of the Court

   In Global-Tech, the plaintiff, SEB, had invented and
patented a deep fryer. A few years later, Sunbeam asked
Pentalpha to supply deep fryers for Sunbeam to sell. To
make the deep fryer, Pentalpha bought an SEB fryer and
copied all but the cosmetic features. Pentalpha then sold
the fryers to Sunbeam, which in turn sold them to custom-
ers. SEB sued Pentalpha for induced infringement, argu-
ing Pentalpha had induced Sunbeam and others to sell the
infringing fryers in violation of SEB’s patent rights. In
defense, Pentalpha argued it did not know the deep fryer
it copied was patented and therefore could not be liable for
inducing anyone to infringe SEB’s patent. The question
presented to this Court was “whether a party who ‘actively
induces infringement of a patent’ under 
35 U.S. C
. §271(b)
must know that the induced acts constitute patent in-
fringement.” Id., at ___ (slip op., at 1).
   After noting the language of §271(b) and the case law
prior to passage of the Patent Act did not resolve the
question, the Global-Tech Court turned to Aro II, a case
about contributory infringement. The Global-Tech Court
deemed that rules concerning contributory infringement
were relevant to induced infringement, because the men-
tal state imposed in each instance is similar. Before the
Patent Act, inducing infringement was not a separate
theory of indirect liability but was evidence of contributory
infringement. 563 U. S., at ___ (slip op., at 5). Thus, in
many respects, it is proper to find common ground in the
two theories of liability.
   Aro II concluded that to be liable for contributory in-
fringement, a defendant must know the acts were infring-
ing. 377 U.S., at 488
. In Global-Tech, the Court said this
reasoning was applicable, explaining as follows:
      “Based on this premise, it follows that the same
    knowledge is needed for induced infringement under
    §271(b). As noted, the two provisions have a common
8         COMMIL USA, LLC v. CISCO SYSTEMS, INC.

                     Opinion of the Court

    origin in the pre-1952 understanding of contributory
    infringement, and the language of the two provisions
    creates the same difficult interpretive choice. It
    would thus be strange to hold that knowledge of the
    relevant patent is needed under §271(c) but not under
    §271(b).
      “Accordingly, we now hold that induced infringe-
    ment under §271(b) requires knowledge that the in-
    duced acts constitute patent infringement.” 563 U. S.,
    at ___ (slip op., at 10).
  In support of Commil, the Government argues against
the clear language of Global-Tech. According to the Gov-
ernment, all Global-Tech requires is knowledge of the
patent: “The Court did not definitively resolve whether
Section 271(b) additionally requires knowledge of the
infringing nature of the induced acts.” Brief for United
States as Amicus Curiae 9. See also Brief for Petitioner
17. Together, Commil and the Government claim the
“factual circumstances” of Global-Tech “did not require”
the Court to decide whether knowledge of infringement is
required for inducement liability. Brief for United States
as Amicus Curiae 12. See also Brief for Petitioner 23–24.
But in the Court’s Global-Tech decision, its description of
the factual circumstances suggests otherwise. The Court
concluded there was enough evidence to support a finding
that Pentalpha knew “the infringing nature of the sales it
encouraged Sunbeam to make.” 563 U. S., at ___ (slip op.,
at 14). It was not only knowledge of the existence of SEB’s
patent that led the Court to affirm the liability finding but
also it was the fact that Pentalpha copied “all but the
cosmetic features of SEB’s fryer,” demonstrating Pental-
pha knew it would be causing customers to infringe SEB’s
patent. Id., at ___ (slip op., at 15).
  Accepting the Government and Commil’s argument
would require this Court to depart from its prior holding.
                  Cite as: 575 U. S. ____ (2015)            9

                      Opinion of the Court

See id., at ___ (slip op., at 10). See also id., at ___
(KENNEDY, J., dissenting) (slip op., at 1) (“The Court is
correct, in my view, to conclude that . . . to induce in-
fringement a defendant must know the acts constitute
patent infringement” (internal quotation marks omitted)).
And the Global-Tech rationale is sound. Qualifying or
limiting its holding, as the Government and Commil seek
to do, would lead to the conclusion, both in inducement
and contributory infringement cases, that a person, or
entity, could be liable even though he did not know the
acts were infringing. In other words, even if the defendant
reads the patent’s claims differently from the plaintiff, and
that reading is reasonable, he would still be liable because
he knew the acts might infringe. Global-Tech requires
more. It requires proof the defendant knew the acts were
infringing. And the Court’s opinion was clear in rejecting
any lesser mental state as the standard. Id., at ___ (slip
op., at 13–14).
                              B
  The question the Court confronts today concerns whether
a defendant’s belief regarding patent validity is a defense
to a claim of induced infringement. It is not. The scienter
element for induced infringement concerns infringement;
that is a different issue than validity. Section 271(b)
requires that the defendant “actively induce[d] infringe-
ment.” That language requires intent to “bring about the
desired result,” which is infringement. Id., at ___ (slip op.,
at 4). And because infringement and validity are separate
issues under the Act, belief regarding validity cannot
negate the scienter required under §271(b).
  When infringement is the issue, the validity of the
patent is not the question to be confronted. In Cardinal
Chemical Co. v. Morton Int’l, Inc., 
508 U.S. 83 
(1993), the
Court explained, “A party seeking a declaratory judgment
of invalidity presents a claim independent of the patent-
10        COMMIL USA, LLC v. CISCO SYSTEMS, INC.

                      Opinion of the Court

ee’s charge of infringement.” 
Id., at 96. 
It further held
noninfringement and invalidity were “alternative grounds”
for dismissing the suit. 
Id., at 98. 
And in Deposit Guaranty
Nat. Bank v. Roper, 
445 U.S. 326 
(1980), the Court
explained that an accused infringer “may prevail either by
successfully attacking the validity of the patent or by
successfully defending the charge of infringement.” 
Id., at
334. 
These explanations are in accord with the long-
accepted truth—perhaps the axiom—that infringement
and invalidity are separate matters under patent law. See
Pandrol USA, LP v. Airboss R. Prods., Inc., 
320 F.3d
1354
, 1365 (CA Fed. 2003).
   Indeed, the issues of infringement and validity appear
in separate parts of the Patent Act. Part III of the Act
deals with “Patents and Protection of Patent Rights,”
including the right to be free from infringement. §§251–
329. Part II, entitled “Patentability of Inventions and
Grants of Patents,” defines what constitutes a valid pa-
tent. §§100–212. Further, noninfringement and invalidity
are listed as two separate defenses, see §§282(b)(1), (2),
and defendants are free to raise either or both of them.
See 
Cardinal, supra, at 98
. Were this Court to interpret
§271(b) as permitting a defense of belief in invalidity, it
would conflate the issues of infringement and validity.
   Allowing this new defense would also undermine a
presumption that is a “common core of thought and truth”
reflected in this Court’s precedents for a century. Radio
Corp. of America v. Radio Engineering Laboratories, Inc.,
293 U.S. 1
, 8 (1934). Under the Patent Act, and the case
law before its passage, a patent is “presumed valid.”
§282(a); 
id., at 8. 
That presumption takes away any need
for a plaintiff to prove his patent is valid to bring a claim.
But if belief in invalidity were a defense to induced in-
fringement, the force of that presumption would be less-
ened to a drastic degree, for a defendant could prevail if he
proved he reasonably believed the patent was invalid.
                  Cite as: 575 U. S. ____ (2015)            11

                      Opinion of the Court

That would circumvent the high bar Congress is presumed
to have chosen: the clear and convincing standard. See
Microsoft Corp. v. i4i Ltd. Partnership, 564 U. S. ___, ___–
___ (2011) (slip op., at 8–10). Defendants must meet that
standard to rebut the presumption of validity. 
Ibid.
   To say that 
an invalid patent cannot be infringed, or
that someone cannot be induced to infringe an invalid
patent, is in one sense a simple truth, both as a matter of
logic and semantics. See M. Swift & Sons, Inc. v. W. H.
Coe Mfg. Co., 
102 F.2d 391
, 396 (CA1 1939). But the
questions courts must address when interpreting and
implementing the statutory framework require a determi-
nation of the procedures and sequences that the parties
must follow to prove the act of wrongful inducement and
any related issues of patent validity. “Validity and in-
fringement are distinct issues, bearing different burdens,
different presumptions, and different 
evidence.”           720
F.3d, at 1374 
(opinion of Newman, J.). To be sure, if at
the end of the day, an act that would have been an in-
fringement or an inducement to infringe pertains to a
patent that is shown to be invalid, there is no patent to be
infringed. But the allocation of the burden to persuade on
these questions, and the timing for the presentations of
the relevant arguments, are concerns of central relevance
to the orderly administration of the patent system.
   Invalidity is an affirmative defense that “can preclude
enforcement of a patent against otherwise infringing
conduct.” 6A Chisum on Patents §19.01, p. 19–5 (2015).
An accused infringer can, of course, attempt to prove that
the patent in suit is invalid; if the patent is indeed invalid,
and shown to be so under proper procedures, there is no
liability. See 
i4i, supra
, at ___–___ (slip op., at 11–12).
That is because invalidity is not a defense to infringement,
it is a defense to liability. And because of that fact, a
belief as to invalidity cannot negate the scienter required
for induced infringement.
12        COMMIL USA, LLC v. CISCO SYSTEMS, INC.

                       Opinion of the Court

   There are also practical reasons not to create a defense
based on a good-faith belief in invalidity. First and fore-
most, accused inducers who believe a patent is invalid
have various proper ways to obtain a ruling to that effect.
They can file a declaratory judgment action asking a
federal court to declare the patent invalid. See MedIm-
mune, Inc. v. Genentech, Inc., 
549 U.S. 118
, 137 (2007).
They can seek inter partes review at the Patent Trial and
Appeal Board and receive a decision as to validity within
12 to 18 months. See §316. Or they can, as Cisco did
here, seek ex parte reexamination of the patent by the
Patent and Trademark Office. §302. And, of course, any
accused infringer who believes the patent in suit is invalid
may raise the affirmative defense of invalidity. §282(b)(2).
If the defendant is successful, he will be immune from
liability.
   Creating a defense of belief in invalidity, furthermore,
would have negative consequences. It can render litiga-
tion more burdensome for everyone involved. Every ac-
cused inducer would have an incentive to put forth a
theory of invalidity and could likely come up with myriad
arguments. See Sloan, Think it is Invalid? A New Defense
to Negate Intent for Induced Infringement, 23 Fed. Cir.
B. J. 613, 618 (2013). And since “it is often more difficult
to determine whether a patent is valid than whether it has
been infringed,” 
Cardinal, 508 U.S., at 99
, accused induc-
ers would likely find it easier to prevail on a defense re-
garding the belief of invalidity than noninfringement. In
addition the need to respond to the defense will increase
discovery costs and multiply the issues the jury must
resolve. Indeed, the jury would be put to the difficult task
of separating the defendant’s belief regarding validity
from the actual issue of validity.
   As a final note, “[o]ur law is . . . no stranger to the possi-
bility that an act may be ‘intentional’ for purposes of civil
liability, even if the actor lacked actual knowledge that
                  Cite as: 575 U. S. ____ (2015)            13

                      Opinion of the Court

her conduct violated the law.” Jerman v. Carlisle, McNel-
lie, Rini, Kramer & Ulrich, L. P. A., 
559 U.S. 573
, 582–
583 (2010). Tortious interference with a contract provides
an apt example. While the invalidity of a contract is a
defense to tortious interference, belief in validity is irrele-
vant. Restatement (Second) of Torts §766, Comment i
(1979). See also W. Keeton, D. Dobbs, R. Keeton, & D.
Owen, Prosser and Keeton on Law of Torts 110 (5th ed.
1984). In a similar way, a trespass “can be committed
despite the actor’s mistaken belief that she has a legal
right to enter the property.” 
Jerman, supra, at 583 
(citing
Restatement (Second) of Torts §164, and Comment e
(1963–1964)). And of course, “[t]he general rule that
ignorance of the law or a mistake of law is no defense to
criminal prosecution is deeply rooted in the American
legal system.” Cheek v. United States, 
498 U.S. 192
, 199
(1991). In the usual case, “I thought it was legal” is no
defense. That concept mirrors this Court’s holding that
belief in invalidity will not negate the scienter required
under §271(b).
                             III
   The Court is well aware that an “industry has developed
in which firms use patents not as a basis for producing
and selling goods but, instead, primarily for obtaining
licensing fees.” eBay Inc. v. MercExchange, L. L. C., 
547
U.S. 388
, 396 (2006) (KENNEDY, J., concurring). Some
companies may use patents as a sword to go after defend-
ants for money, even when their claims are frivolous. This
tactic is often pursued through demand letters, which
“may be sent very broadly and without prior investigation,
may assert vague claims of infringement, and may be
designed to obtain payments that are based more on the
costs of defending litigation than on the merit of the pa-
tent claims.” L. Greisman, Prepared Statement of the
Federal Trade Commission on Discussion Draft of Patent
14        COMMIL USA, LLC v. CISCO SYSTEMS, INC.

                     Opinion of the Court

Demand Letter Legislation before the Subcommittee on
Commerce, Manufacturing, and Trade of the House Com-
mittee on Energy and Commerce 2 (2014). This behavior
can impose a “harmful tax on innovation.” 
Ibid.
  No issue of 
frivolity has been raised by the parties in
this case, nor does it arise on the facts presented to this
Court. Nonetheless, it is still necessary and proper to
stress that district courts have the authority and respon-
sibility to ensure frivolous cases are dissuaded. If frivo-
lous cases are filed in federal court, it is within the power
of the court to sanction attorneys for bringing such suits.
Fed. Rule Civ. Proc. 11. It is also within the district
court’s discretion to award attorney’s fees to prevailing
parties in “exceptional cases.” 
35 U.S. C
. §285; see also
Octane Fitness, LLC v. ICON Health & Fitness, Inc., 572
U. S. ___, ___–___ (2014) (slip op., at 7–8). These safe-
guards, combined with the avenues that accused inducers
have to obtain rulings on the validity of patents, militate
in favor of maintaining the separation expressed through-
out the Patent Act between infringement and validity.
This dichotomy means that belief in invalidity is no de-
fense to a claim of induced infringement.
  The judgment of the United States Court of Appeals for
the Federal Circuit is vacated, and the case is remanded
for further proceedings consistent with this opinion.

                                             It is so ordered.

  JUSTICE BREYER took no part in the consideration or
decision of this case.
                  Cite as: 575 U. S. ____ (2015)            1

                      SCALIA, J., dissenting

SUPREME COURT OF THE UNITED STATES
                          _________________

                           No. 13–896
                          _________________


          COMMIL USA, LLC, PETITIONER v. 

              CISCO SYSTEMS, INC.

 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

           APPEALS FOR THE FEDERAL CIRCUIT

                         [May 26, 2015] 


   JUSTICE SCALIA, with whom THE CHIEF JUSTICE joins,
dissenting.
   I agree with the Court’s rejection of the main argument
advanced by Commil and the United States, that induced
infringement under 
35 U.S. C
. §271(b) does not “requir[e]
knowledge of the infringing nature of the induced acts.”
Brief for United States as Amicus Curiae 9; see also Brief
for Petitioner 15–44. I disagree, however, with the Court’s
holding that good-faith belief in a patent’s invalidity is not
a defense to induced infringement.
   Infringing a patent means invading a patentee’s exclu-
sive right to practice his claimed invention. Crown Die &
Tool Co. v. Nye Tool & Machine Works, 
261 U.S. 24
, 40
(1923) (quoting 3 W. Robinson, Law of Patents §937, pp.
122–123 (1890)). Only valid patents confer this right to
exclusivity—invalid patents do not. FTC v. Actavis, Inc.,
570 U. S. ___, ___ (2013) (slip op., at 8). It follows, as
night the day, that only valid patents can be infringed. To
talk of infringing an invalid patent is to talk nonsense.
   Induced infringement, we have said, “requires
knowledge that the induced acts constitute patent in-
fringement.” Global-Tech Appliances, Inc. v. SEB S. A.,
563 U. S. ___, ___ (2011) (slip op., at 10). Because only
valid patents can be infringed, anyone with a good-faith
belief in a patent’s invalidity necessarily believes the
2         COMMIL USA, LLC v. CISCO SYSTEMS, INC.

                     SCALIA, J., dissenting

patent cannot be infringed. And it is impossible for any-
one who believes that a patent cannot be infringed to
induce actions that he knows will infringe it. A good-faith
belief that a patent is invalid is therefore a defense to
induced infringement of that patent.
   The Court makes four arguments in support of the
contrary position. None seems to me persuasive. First, it
notes that the Patent Act treats infringement and validity
as distinct issues. Ante, at 9–10. That is true. It is also
irrelevant. Saying that infringement cannot exist without
a valid patent does not “conflate the issues of infringement
and validity,” ante, at 10, any more than saying that water
cannot exist without oxygen “conflates” water and oxygen.
Recognizing that infringement requires validity is entirely
consistent with the “long-accepted truth . . . that infringe-
ment and invalidity are separate matters under patent
law.” 
Ibid.
   The Court next 
insists that permitting the defense at
issue would undermine the statutory presumption of
validity. Ante, at 10–11. It would do no such thing. By
reason of the statutory presumption of validity, §282(a),
patents can be held invalid only by “clear and convincing
evidence.” Microsoft Corp. v. i4i Ltd. Partnership, 564
U. S. ___, ___ (2011) (slip op., at 1). This presumption is
not weakened by treating a good-faith belief in invalidity
as a defense to induced infringement. An alleged inducer
who succeeds in this defense does not thereby call a pa-
tent’s validity into question. He merely avoids liability for
a third party’s infringement of a valid patent, in no way
undermining that patent’s presumed validity.
   Next, the Court says that “invalidity is not a defense to
infringement, it is a defense to liability.” Ante, at 11.
That is an assertion, not an argument. Again, to infringe
a patent is to invade the patentee’s right of exclusivity.
An invalid patent confers no such right. How is it possible
to interfere with rights that do not exist? The Court has
                 Cite as: 575 U. S. ____ (2015)            3

                     SCALIA, J., dissenting

no answer.
   That brings me to the Court’s weakest argument: that
there are “practical reasons not to create a defense based
on a good-faith belief in invalidity.” Ante, at 12 (emphasis
added); see also 
ibid. (“Creating a defense 
of belief in
invalidity, furthermore, would have negative consequences”
(emphasis added)). Ours is not a common-law court.
Erie R. Co. v. Tompkins, 
304 U.S. 64
, 78 (1938). We do
not, or at least should not, create defenses to statutory
liability—and that is not what this dissent purports to do.
Our task is to interpret the Patent Act, and to decide
whether it makes a good-faith belief in a patent’s invalid-
ity a defense to induced infringement. Since, as we said in
Global-Tech, supra
, the Act makes knowledge of infringe-
ment a requirement for induced-infringement liability;
and since there can be no infringement (and hence no
knowledge of infringement) of an invalid patent; good-
faith belief in invalidity is a defense. I may add, however,
that if the desirability of the rule we adopt were a proper
consideration, it is by no means clear that the Court’s
holding, which increases the in terrorem power of patent
trolls, is preferable. The Court seemingly acknowledges
that consequence in Part III of its opinion.
   For the foregoing reasons, I respectfully dissent.