(Slip Opinion)              OCTOBER TERM, 2013                                       1

                                       Syllabus

         NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
       being done in connection with this case, at the time the opinion is issued.
       The syllabus constitutes no part of the opinion of the Court but has been
       prepared by the Reporter of Decisions for the convenience of the reader.
       See United States v. Detroit Timber & Lumber Co., 

, 337.


SUPREME COURT OF THE UNITED STATES

                                       Syllabus

     NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

CERTIORARI TO THE UNITED STATES COURT OF APPEALS FOR
                THE FEDERAL CIRCUIT

       No. 13–369.      Argued April 28, 2014—Decided June 2, 2014
The Patent Act requires that a patent specification “conclude with one
  or more claims particularly pointing out and distinctly claiming the
  subject matter which the applicant regards as [the] invention.” 

. §112, ¶2. This case concerns the proper reading of the stat­
  ute’s clarity and precision demand.
     Assigned to respondent Biosig Instruments, Inc., the patent in dis­
  pute (the ’753 patent) involves a heart-rate monitor used with exer­
  cise equipment. Prior heart-rate monitors, the patent asserts, were
  often inaccurate in measuring the electrical signals accompanying
  each heartbeat (electrocardiograph or ECG signals) because of the
  presence of other electrical signals (electromyogram or EMG signals),
  generated by the user’s skeletal muscles, that can impede ECG signal
  detection. The invention claims to improve on prior art by detecting
  and processing ECG signals in a way that filters out the EMG inter­
  ference.
     Claim 1 of the ’753 patent, which contains the limitations critical to
  this dispute, refers to a “heart rate monitor for use by a user in asso­
  ciation with exercise apparatus and/or exercise procedures.” The
  claim “comprise[s],” among other elements, a cylindrical bar fitted
  with a display device; “electronic circuitry including a difference am­
  plifier”; and, on each half of the cylindrical bar, a “live” electrode and
  a “common” electrode “mounted . . . in spaced relationship with each
  other.”
     Biosig filed this patent infringement suit, alleging that Nautilus,
  Inc., without obtaining a license, sold exercise machines containing
  Biosig’s patented technology. The District Court, after conducting a
  hearing to determine the proper construction of the patent’s claims,
  granted Nautilus’ motion for summary judgment on the ground that
2          NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

                                 Syllabus

    the claim term “in spaced relationship with each other” failed §112,
    ¶2’s definiteness requirement. The Federal Circuit reversed and re­
    manded, concluding that a patent claim passes the §112, ¶2 thresh­
    old so long as the claim is “amenable to construction,” and the claim,
    as construed, is not “insolubly ambiguous.” Under that standard, the
    court determined, the ’753 patent survived indefiniteness review.
Held:
    1. A patent is invalid for indefiniteness if its claims, read in light of
 the patent’s specification and prosecution history, fail to inform, with
 reasonable certainty, those skilled in the art about the scope of the
 invention. The parties agree that definiteness is to be evaluated from
 the perspective of a person skilled in the relevant art, that claims are
 to be read in light of the patent’s specification and prosecution histo­
 ry, and that definiteness is to be measured as of the time of the pa­
 tent application. The parties disagree as to how much imprecision
 §112, ¶2 tolerates.
    Section 112’s definiteness requirement must take into account the
 inherent limitations of language. See Festo Corp. v. Shoketsu Kinzo-
 ku Kogyo Kabushiki Co., 

, 731. On the one hand, some
 modicum of uncertainty is the “price of ensuring the appropriate in­
 centives for innovation,” 

and patents are “not addressed to
 lawyers, or even to the public generally,” but to those skilled in the
 relevant art, Carnegie Steel Co. v. Cambria Iron Co., 

,
 437. At the same time, a patent must be precise enough to afford
 clear notice of what is claimed, thereby “ ‘appris[ing] the public of
 what is still open to them,’ ” Markman v. Westview Instruments, Inc.,
 

, 373, in a manner that avoids “[a] zone of uncertainty
 which enterprise and experimentation may enter only at the risk of
 infringement claims,” United Carbon Co. v. Binney & Smith Co., 

, 236. The standard adopted here mandates clarity, while
 recognizing that absolute precision is unattainable. It also accords
 with opinions of this Court stating that “the certainty which the law
 requires in patents is not greater than is reasonable, having regard
 to their subject-matter.” Minerals Separation, Ltd. v. Hyde, 

, 270. Pp. 8–11.
    2. The Federal Circuit’s standard, which tolerates some ambiguous
 claims but not others, does not satisfy the statute’s definiteness re­
 quirement. The Court of Appeals inquired whether the ’753 patent’s
 claims were “amenable to construction” or “insolubly ambiguous,” but
 such formulations lack the precision §112, ¶2 demands. To tolerate
 imprecision just short of that rendering a claim “insolubly ambigu­
 ous” would diminish the definiteness requirement’s public-notice
 function and foster the innovation-discouraging “zone of uncertainty,”
 United 

, against which this Court has
                      Cite as: 572 U. S. ____ (2014)                       3

                                 Syllabus

  warned. While some of the Federal Circuit’s fuller explications of the
  term “insolubly ambiguous” may come closer to tracking the statuto­
  ry prescription, this Court must ensure that the Federal Circuit’s test
  is at least “probative of the essential inquiry.” Warner-Jenkinson Co.
  v. Hilton Davis Chemical Co., 

, 40. The expressions “in­
  solubly ambiguous” and “amenable to construction,” which permeate
  the Federal Circuit’s recent decisions concerning §112, ¶2, fall short
  in this regard and can leave courts and the patent bar at sea without
  a reliable compass. Pp. 11–13.
     3. This Court, as “a court of review, not of first view,” Cutter v. Wil-
  kinson, 

, 718, n. 7, follows its ordinary practice of re­
  manding so that the Federal Circuit can reconsider, under the proper
  standard, whether the relevant claims in the ’753 patent are suffi­
  ciently definite, see, e.g., Johnson v. California, 

, 515.
  Pp. 13–14.

, vacated and remanded.

  GINSBURG, J., delivered the opinion for a unanimous Court.
                        Cite as: 572 U. S. ____ (2014)                              1

                             Opinion of the Court
     NOTICE: This opinion is subject to formal revision before publication in the
     preliminary print of the United States Reports. Readers are requested to
     notify the Reporter of Decisions, Supreme Court of the United States, Wash­
     ington, D. C. 20543, of any typographical or other formal errors, in order
     that corrections may be made before the preliminary print goes to press.


SUPREME COURT OF THE UNITED STATES
                                   _________________

                                   No. 13–369
                                   _________________


        NAUTILUS, INC., PETITIONER v. BIOSIG 

               INSTRUMENTS, INC.

 ON WRIT OF CERTIORARI TO THE UNITED STATES COURT OF 

           APPEALS FOR THE FEDERAL CIRCUIT

                                 [June 2, 2014]


   JUSTICE GINSBURG delivered the opinion of the Court.
   The Patent Act requires that a patent specification
“conclude with one or more claims particularly pointing
out and distinctly claiming the subject matter which the
applicant regards as [the] invention.” 

. §112, ¶2
(2006 ed.) (emphasis added). This case, involving a heart­
rate monitor used with exercise equipment, concerns the
proper reading of the statute’s clarity and precision de­
mand. According to the Federal Circuit, a patent claim
passes the §112, ¶2 threshold so long as the claim is
“amenable to construction,” and the claim, as construed, is
not “insolubly ambiguous.” 

, 898–899 (2013).
We conclude that the Federal Circuit’s formulation, which
tolerates some ambiguous claims but not others, does not
satisfy the statute’s definiteness requirement. In place of
the “insolubly ambiguous” standard, we hold that a patent
is invalid for indefiniteness if its claims, read in light of
the specification delineating the patent, and the prosecu­
tion history, fail to inform, with reasonable certainty,
those skilled in the art about the scope of the invention.
Expressing no opinion on the validity of the patent-in-suit,
2       NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

                      Opinion of the Court

we remand, instructing the Federal Circuit to decide the
case employing the standard we have prescribed.
                                I
   Authorized by the Constitution “[t]o promote the Pro­
gress of Science and useful Arts, by securing for limited
Times to . . . Inventors the exclusive Right to their . . .
Discoveries,” Art. I, §8, cl. 8, Congress has enacted patent
laws rewarding inventors with a limited monopoly.
“Th[at] monopoly is a property right,” and “like any prop­
erty right, its boundaries should be clear.” Festo Corp. v.
Shoketsu Kinzoku Kogyo Kabushiki Co., 

, 730
(2002). See also Markman v. Westview Instruments, Inc.,

, 373 (1996) (“It has long been understood
that a patent must describe the exact scope of an inven­
tion and its manufacture . . . .”). Thus, when Congress
enacted the first Patent Act in 1790, it directed that pa­
tent grantees file a written specification “containing a
description . . . of the thing or things . . . invented or dis­
covered,” which “shall be so particular” as to “distinguish
the invention or discovery from other things before known
and used.” Act of Apr. 10, 1790, §2, 1 Stat. 110.
   The patent laws have retained this requirement of
definiteness even as the focus of patent construction has
shifted. Under early patent practice in the United States,
we have recounted, it was the written specification that
“represented the key to the patent.” 

. Eventually, however, patent applicants began to
set out the invention’s scope in a separate section known
as the “claim.” See generally 1 R. Moy, Walker on Patents
§4.2, pp. 4–17 to 4–20 (4th ed. 2012). The Patent Act of
1870 expressly conditioned the receipt of a patent on the
inventor’s inclusion of one or more such claims, described
with particularity and distinctness. See Act of July 8,
1870, §26, 16 Stat. 201 (to obtain a patent, the inventor
must “particularly point out and distinctly claim the part,
                      Cite as: 572 U. S. ____ (2014)                      3

                           Opinion of the Court

improvement, or combination which [the inventor] claims
as his invention or discovery”).
  The 1870 Act’s definiteness requirement survives today,
largely unaltered. Section 112 of the Patent Act of 1952,
applicable to this case, requires the patent applicant to
conclude the specification with “one or more claims partic­
ularly pointing out and distinctly claiming the subject
matter which the applicant regards as his invention.” 

. §112, ¶2 (2006 ed.). A lack of definiteness renders
invalid “the patent or any claim in suit.” §282, ¶2(3).1
                            II

                            A

  The patent in dispute, U. S. Patent No. 5,337,753 (’753
patent), issued to Dr. Gregory Lekhtman in 1994 and
assigned to respondent Biosig Instruments, Inc., concerns
a heart-rate monitor for use during exercise. Previous
heart-rate monitors, the patent asserts, were often inaccu­
rate in measuring the electrical signals accompanying
each heartbeat (electrocardiograph or ECG signals). The
inaccuracy was caused by electrical signals of a different
sort, known as electromyogram or EMG signals, generated
by an exerciser’s skeletal muscles when, for example, she
moves her arm, or grips an exercise monitor with her
hand. These EMG signals can “mask” ECG signals and
thereby impede their detection. App. 52, 147.
——————
  1 In the Leahy-Smith America Invents Act, Pub. L. 112–29, 125 Stat.
284, enacted in 2011, Congress amended several parts of the Patent
Act. Those amendments modified §§112 and 282 in minor respects not
pertinent here. In any event, the amended versions of those provisions
are inapplicable to patent applications filed before September 16, 2012,
and proceedings commenced before September 16, 2011. See §§4(e),
15(c), 20(l), 125 Stat. 297, 328, 335, notes following 

. §§2, 111,
119. Here, the application for the patent-in-suit was filed in 1992, and
the relevant court proceedings were initiated in 2010. Accordingly, this
opinion’s citations to the Patent Act refer to the 2006 edition of the
United States Code.
4         NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

                          Opinion of the Court

   Dr. Lekhtman’s invention claims to improve on prior art
by eliminating that impediment. The invention focuses on
a key difference between EMG and ECG waveforms: while
ECG signals detected from a user’s left hand have a polar­
ity opposite to that of the signals detected from her right
hand,2 EMG signals from each hand have the same polar-
ity. The patented device works by measuring equalized
EMG signals detected at each hand and then using cir­
cuitry to subtract the identical EMG signals from each
other, thus filtering out the EMG interference.
   As relevant here, the ’753 patent describes a heart-rate
monitor contained in a hollow cylindrical bar that a user
grips with both hands, such that each hand comes into
contact with two electrodes, one “live” and one “common.”
The device is illustrated in figure 1 of the patent, 

reproduced in the Appendix to this opinion.
   Claim 1 of the ’753 patent, which contains the limita­
tions critical to this dispute, refers to a “heart rate monitor
for use by a user in association with exercise apparatus
and/or exercise procedures.” 

The claim “com­
prise[s],” among other elements, an “elongate member”
(cylindrical bar) with a display device; “electronic circuitry
including a difference amplifier”; and, on each half of the
cylindrical bar, a live electrode and a common electrode
“mounted . . . in spaced relationship with each other.”
Ibid.3 The claim sets forth additional elements, including
that the cylindrical bar is to be held in such a way that
each of the user’s hands “contact[s]” both electrodes on
each side of the bar. 

Further, the EMG signals
detected by the two electrode pairs are to be “of substan­
——————
  2 This difference in polarity occurs because the heart is not aligned

vertically in relation to the center of the body; the organ tilts leftward
from apex to bottom. App. 213.
  3 As depicted in figure 1 of the patent, 

reproduced in the

Appendix to this opinion, the live electrodes are identified by numbers
9 and 13, and the common electrodes, by 11 and 15.
                 Cite as: 572 U. S. ____ (2014)           5

                     Opinion of the Court

tially equal magnitude and phase” so that the difference
amplifier will “produce a substantially zero [EMG] signal”
upon subtracting the signals from one another. 

between the parties arose in the 1990’s,
when Biosig allegedly disclosed the patented technology to
StairMaster Sports Medical Products, Inc. According to
Biosig, StairMaster, without ever obtaining a license, sold
exercise machines that included Biosig’s patented technol­
ogy, and petitioner Nautilus, Inc., continued to do so after
acquiring the StairMaster brand. In 2004, based on these
allegations, Biosig brought a patent infringement suit
against Nautilus in the U. S. District Court for the South­
ern District of New York.
  With Biosig’s lawsuit launched, Nautilus asked the U. S.
Patent and Trademark Office (PTO) to reexamine the ’753
patent.     The reexamination proceedings centered on
whether the patent was anticipated or rendered obvious
by prior art—principally, a patent issued in 1984 to an
inventor named Fujisaki, which similarly disclosed a
heart-rate monitor using two pairs of electrodes and a
difference amplifier. Endeavoring to distinguish the ’753
patent from prior art, Biosig submitted a declaration from
Dr. Lekhtman. The declaration attested, among other
things, that the ’753 patent sufficiently informed a person
skilled in the art how to configure the detecting electrodes
so as “to produce equal EMG [signals] from the left and
right hands.” 

Although the electrodes’ design
variables—including spacing, shape, size, and material—
cannot be standardized across all exercise machines, Dr.
Lekhtman explained, a skilled artisan could undertake a
“trial and error” process of equalization. This would entail
experimentation with different electrode configurations in
order to optimize EMG signal cancellation. 

6        NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

                          Opinion of the Court

156, 158.4 In 2010, the PTO issued a determination con­
firming the patentability of the ’753 patent’s claims.
   Biosig thereafter reinstituted its infringement suit,
which the parties had voluntarily dismissed without prej­
udice while PTO reexamination was underway. In 2011,
the District Court conducted a hearing to determine the
proper construction of the patent’s claims, see Markman v.
Westview Instruments, Inc., 

(1996) (claim
construction is a matter of law reserved for court decision),
including the claim term “in spaced relationship with each
other.” According to Biosig, that “spaced relationship”
referred to the distance between the live electrode and the
common electrode in each electrode pair. Nautilus, seizing
on Biosig’s submissions to the PTO during the reexamina­
tion, maintained that the “spaced relationship” must be a
distance “greater than the width of each electrode.” App.
245. The District Court ultimately construed the term to
mean “there is a defined relationship between the live
electrode and the common electrode on one side of the
cylindrical bar and the same or a different defined rela­
tionship between the live electrode and the common elec­
trode on the other side of the cylindrical bar,” without any
reference to the electrodes’ width. App. to Pet. for Cert.
43a–44a.
   Nautilus moved for summary judgment, arguing that
the term “spaced relationship,” as construed, was indefi­
nite under §112, ¶2. The District Court granted the mo­
tion. Those words, the District Court concluded, “did not
tell [the court] or anyone what precisely the space should
——————
   4 Dr. Lekhtman’s declaration also referred to an expert report pre­

pared by Dr. Henrietta Galiana, Chair of the Department of Biomedical
Engineering at McGill University, for use in the infringement litiga­
tion. That report described how Dr. Galiana’s laboratory technician,
equipped with a wooden dowel, wire, metal foil, glue, electrical tape,
and the drawings from the ’753 patent, was able in two hours to build a
monitor that “worked just as described in the . . . patent.” 

                 Cite as: 572 U. S. ____ (2014)           7

                     Opinion of the Court

be,” or even supply “any parameters” for determining the
appropriate spacing. 

   The Federal Circuit reversed and remanded. A claim is
indefinite, the majority opinion stated, “only when it is
‘not amenable to construction’ or ‘insolubly ambiguous.’ ”

, 898 (2013) (quoting Datamize, LLC v.
Plumtree Software, Inc., 

, 1347 (CA Fed.
2005)). Under that standard, the majority determined, the
’753 patent survived indefiniteness review. Considering
first the “intrinsic evidence”—i.e., the claim language, the
specification, and the prosecution history—the majority
discerned “certain inherent parameters of the claimed
apparatus, which to a skilled artisan may be sufficient to
understand the metes and bounds of ‘spaced relation­
ship.’ 

. These sources of meaning, the
majority explained, make plain that the distance separat­
ing the live and common electrodes on each half of the bar
“cannot be greater than the width of a user’s hands”; that
is so “because claim 1 requires the live and common elec­
trodes to independently detect electrical signals at two
distinct points of a hand.” 

ity noted, the intrinsic evidence teaches that this distance
cannot be “infinitesimally small, effectively merging the
live and common electrodes into a single electrode with
one detection point.” 

provi­
sions, the majority went on to observe, shed additional
light on the meaning of “spaced relationship.” Surveying
the record before the PTO on reexamination, the majority
concluded that a skilled artisan would know that she could
attain the indicated functions of equalizing and removing
EMG signals by adjusting design variables, including
spacing.
   In a concurring opinion, Judge Schall reached the ma­
jority’s result employing “a more limited analysis.” 

Judge Schall accepted the majority’s recitation of the
definiteness standard, under which claims amenable to
8       NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

                     Opinion of the Court

construction are nonetheless indefinite when “the con­
struction remains insolubly ambiguous.” 

omitted). The District Court’s construc­
tion of “spaced relationship,” Judge Schall maintained,
was sufficiently clear: the term means “there is a fixed
spatial relationship between the live electrode and the
common electrode” on each side of the cylindrical bar.

with the majority that the
intrinsic evidence discloses inherent limits of that spacing.
But, unlike the majority, Judge Schall did not “presum[e]
a functional linkage between the ‘spaced relationship’
limitation and the removal of EMG signals.” 

Other limitations of the claim, in his view, and not the
“ ‘spaced relationship’ limitation itself,” “included a func­
tional requirement to remove EMG signals.” 

571 U. S. ___ (2014), and now
vacate and remand.
                              III
                               A
   Although the parties here disagree on the dispositive
question—does the ’753 patent withstand definiteness
scrutiny—they are in accord on several aspects of the
§112, ¶2 inquiry. First, definiteness is to be evaluated
from the perspective of someone skilled in the relevant art.
See, e.g., General Elec. Co. v. Wabash Appliance Corp., 

, 371 (1938). See also §112, ¶1 (patent’s specifi­
cation “shall contain a written description of the invention,
and of the manner and process of making and using it, in
such full, clear, concise, and exact terms as to enable any
person skilled in the art to which it pertains, or with which
it is most nearly connected, to make and use the same”
(emphasis added)). Second, in assessing definiteness,
claims are to be read in light of the patent’s specification
and prosecution history. See, e.g., United States v. Adams,

, 48–49 (1966) (specification); Festo Corp. v.
                     Cite as: 572 U. S. ____ (2014)                9

                         Opinion of the Court

Shoketsu Kinzoku Kogyo Kabushiki Co., 

, 741
(2002) (prosecution history). Third, “[d]efiniteness is
measured from the viewpoint of a person skilled in [the]
art at the time the patent was filed.” Brief for Respondent
55 (emphasis added). See generally Sarnoff & Manzo, An
Introduction to, Premises of, and Problems With Patent
Claim Construction, in Patent Claim Construction in the
Federal Circuit 9 (E. Manzo ed. 2014) (“Patent claims . . .
should be construed from an objective perspective of a
[skilled artisan], based on what the applicant actually
claimed, disclosed, and stated during the application
process.”).
   The parties differ, however, in their articulations of just
how much imprecision §112, ¶2 tolerates. In Nautilus’
view, a patent is invalid when a claim is “ambiguous, such
that readers could reasonably interpret the claim’s scope
differently.” Brief for Petitioner 37. Biosig and the Solici­
tor General would require only that the patent provide
reasonable notice of the scope of the claimed invention.
See Brief for Respondent 18; Brief for United States as
Amicus Curiae 9–10.
   Section 112, we have said, entails a “delicate balance.”

. On the one hand, the definiteness
requirement must take into account the inherent limita­
tions of language. See 

uncertainty,
the Court has recognized, is the “price of ensuring the
appropriate incentives for innovation.” 

One
must bear in mind, moreover, that patents are “not ad­
dressed to lawyers, or even to the public generally,” but
rather to those skilled in the relevant art. Carnegie Steel
Co. v. Cambria Iron Co., 

, 437 (1902) (also
stating that “any description which is sufficient to apprise
[steel manufacturers] in the language of the art of the
definite feature of the invention, and to serve as a warning
to others of what the patent claims as a monopoly, is
sufficiently definite to sustain the patent”).5
——————
 5 See   also Eibel Process Co. v. Minnesota & Ontario Paper Co., 261
10        NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

                           Opinion of the Court

   At the same time, a patent must be precise enough to
afford clear notice of what is claimed, thereby “ ‘appris[ing]
the public of what is still open to them.’ ” 

(quoting McClain v. Ortmayer, 

,
424 (1891)).6 Otherwise there would be “[a] zone of uncer­
tainty which enterprise and experimentation may enter
only at the risk of infringement claims.” United Carbon
Co. v. Binney & Smith Co., 

, 236 (1942). And
absent a meaningful definiteness check, we are told, pa­
tent applicants face powerful incentives to inject ambigu-
ity into their claims. See Brief for Petitioner 30–32 (citing
patent treatises and drafting guides). See also Federal
Trade Commission, The Evolving IP Marketplace: Align­
ing Patent Notice and Remedies With Competition 85
(2011) (quoting testimony that patent system fosters “an
incentive to be as vague and ambiguous as you can with
your claims” and “defer clarity at all costs”).7 Eliminating
that temptation is in order, and “the patent drafter is in
the best position to resolve the ambiguity in . . . patent
——————
U. S. 45, 58, 65–66 (1923) (upholding as definite a patent for an im­
provement to a paper-making machine, which provided that a wire be
placed at a “high” or “substantial elevation,” where “readers . . . skilled
in the art of paper making and versed in the use of the . . . machine”
would have “no difficulty . . . in determining . . . the substantial [eleva­
tion] needed” for the machine to operate as specified).
   6 See also United Carbon Co. v. Binney & Smith Co., 

,

236 (1942) (“The statutory requirement of particularity and distinct­
ness in claims is met only when they clearly distinguish what is
claimed from what went before in the art and clearly circumscribe what
is foreclosed from future enterprise.”); General Elec. Co. v. Wabash
Appliance Corp., 

, 369 (1938) (“The limits of a patent must
be known for the protection of the patentee, the encouragement of the
inventive genius of others and the assurance that the subject of the
patent will be dedicated ultimately to the public.”).
   7 Online at http: / / www. ftc.gov / sites / default / files / documents /

reports/evolving-ip-marketplace-aligning-patent-notice-and-remedies-
competition - report -federal- trade / 110307patentreport.pdf (as visited
May 30, 2014, and available in Clerk of Court’s case file).
                      Cite as: 572 U. S. ____ (2014)                       11

                           Opinion of the Court

claims.” Halliburton Energy Servs., Inc. v. M–I LLC, 

, 1255 (CA Fed. 2008). See also Hormone Re-
search Foundation, Inc. v. Genentech, Inc., 

,
1563 (CA Fed. 1990) (“It is a well-established axiom in
patent law that a patentee is free to be his or her own
lexicographer . . . .”).
  To determine the proper office of the definiteness com­
mand, therefore, we must reconcile concerns that tug in
opposite directions. Cognizant of the competing concerns,
we read §112, ¶2 to require that a patent’s claims, viewed
in light of the specification and prosecution history, inform
those skilled in the art about the scope of the invention
with reasonable certainty. The definiteness requirement,
so understood, mandates clarity, while recognizing that
absolute precision is unattainable. The standard we adopt
accords with opinions of this Court stating that “the cer­
tainty which the law requires in patents is not greater
than is reasonable, having regard to their subject-matter.”
Minerals Separation, Ltd. v. Hyde, 

, 270
(1916). See also United 

(“claims
must be reasonably clear-cut”); 

(claim construction calls for “the necessarily sophisti­
cated analysis of the whole document,” and may turn on
evaluations of expert testimony).
                            B
  In resolving Nautilus’ definiteness challenge, the Fed-
eral Circuit asked whether the ’753 patent’s claims were
“amenable to construction” or “insolubly ambiguous.”
Those formulations can breed lower court confusion,8 for
——————
   8 See, e.g., Every Penny Counts, Inc. v. Wells Fargo Bank, N. A., ___

F. Supp. 2d ___, ___, 

, *4 (MD Fla., Mar. 5, 2014)
(finding that “the account,” as used in claim, “lacks definiteness,”
because it might mean several different things and “no informed and
confident choice is available among the contending definitions,” but
that “the extent of the indefiniteness . . . falls far short of the ‘insoluble
12       NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

                        Opinion of the Court

they lack the precision §112, ¶2 demands. It cannot be
sufficient that a court can ascribe some meaning to a
patent’s claims; the definiteness inquiry trains on the
understanding of a skilled artisan at the time of the pa­
tent application, not that of a court viewing matters
post hoc. To tolerate imprecision just short of that render­
ing a claim “insolubly ambiguous” would diminish the
definiteness requirement’s public-notice function and
foster the innovation-discouraging “zone of uncertainty,”
United 

, against which this Court
has warned.
   Appreciating that “terms like ‘insolubly ambiguous’ may
not be felicitous,” Brief for Respondent 34, Biosig argues
the phrase is a shorthand label for a more probing inquiry
that the Federal Circuit applies in practice. The Federal
Circuit’s fuller explications of the term “insolubly ambigu­
ous,” we recognize, may come closer to tracking the statu­
tory prescription. See, 

(case below)
(“[I]f reasonable efforts at claim construction result in a
definition that does not provide sufficient particularity
and clarity to inform skilled artisans of the bounds of the
claim, the claim is insolubly ambiguous and invalid for
indefiniteness.” (internal quotation marks omitted)). But
although this Court does not “micromanag[e] the Federal
Circuit’s particular word choice” in applying patent-law
doctrines, we must ensure that the Federal Circuit’s test is
at least “probative of the essential inquiry.” Warner-
Jenkinson Co. v. Hilton Davis Chemical Co., 

,
40 (1997). Falling short in that regard, the expressions
“insolubly ambiguous” and “amenable to construction”
permeate the Federal Circuit’s recent decisions concerning
§112, ¶2’s requirement.9 We agree with Nautilus and its
——————
ambiguity’ required to invalidate the claim”).
  9 E.g., Hearing Components, Inc. v. Shure Inc., 

, 1366

(CA Fed. 2010) (“the definiteness of claim terms depends on whether
                      Cite as: 572 U. S. ____ (2014)                     13

                           Opinion of the Court

amici that such terminology can leave courts and the
patent bar at sea without a reliable compass.10
                            IV
  Both here and in the courts below, the parties have
advanced conflicting arguments as to the definiteness of
the claims in the ’753 patent. Nautilus maintains that the
claim term “spaced relationship” is open to multiple inter­
pretations reflecting markedly different understandings of
——————
those terms can be given any reasonable meaning”); Datamize, LLC v.
Plumtree Software, Inc., 

, 1347 (CA Fed. 2005) (“Only
claims ‘not amenable to construction’ or ‘insolubly ambiguous’ are
indefinite.”); Exxon Research & Engineering Co. v. United States, 

, 1375 (CA Fed. 2001) (“If a claim is insolubly ambiguous,
and no narrowing construction can properly be adopted, we have held
the claim indefinite.”). See also Dept. of Commerce, Manual of Patent
Examining Procedure §2173.02(I), p. 294 (9th ed. 2014) (PTO manual
describing Federal Circuit’s test as upholding a claim’s validity “if some
meaning can be gleaned from the language”).
    10 The Federal Circuit suggests that a permissive definiteness stand­

ard “ ‘accord[s] respect to the statutory presumption of patent validity.’ ”

, 902 (2013) (quoting Exxon 

).
See also §282, ¶1 (“[a] patent shall be presumed valid,” and “[t]he
burden of establishing invalidity of a patent or any claim thereof shall
rest on the party asserting such invalidity”); Microsoft Corp. v. i4i Ltd.
Partnership, 564 U. S. ___, ___ (2011) (slip op., at 1) (invalidity defenses
must be proved by “clear and convincing evidence”). As the parties
appear to agree, however, this presumption of validity does not alter
the degree of clarity that §112, ¶2 demands from patent applicants; to
the contrary, it incorporates that definiteness requirement by refer­
ence. See §282, ¶2(3) (defenses to infringement actions include
“[i]nvalidity of the patent or any claim in suit for failure to comply with
. . . any requirement of [§112]”).
    The parties nonetheless dispute whether factual findings subsidiary
to the ultimate issue of definiteness trigger the clear-and-convincing­
evidence standard and, relatedly, whether deference is due to the PTO’s
resolution of disputed issues of fact. We leave these questions for
another day. The court below treated definiteness as “a legal issue
[the] court reviews without 

, and Biosig has
not called our attention to any contested factual matter—or PTO
determination thereof—pertinent to its infringement claims.
14       NAUTILUS, INC. v. BIOSIG INSTRUMENTS, INC.

                        Opinion of the Court

the patent’s scope, as exemplified by the disagreement
among the members of the Federal Circuit panel.11 Biosig
responds that “spaced relationship,” read in light of the
specification and as illustrated in the accompanying draw­
ings, delineates the permissible spacing with sufficient
precision.
   “[M]indful that we are a court of review, not of first
view,” Cutter v. Wilkinson, 

, 718, n. 7 (2005),
we decline to apply the standard we have announced to
the controversy between Nautilus and Biosig. As we have
explained, the Federal Circuit invoked a standard more
amorphous than the statutory definiteness requirement
allows. We therefore follow our ordinary practice of re­
manding so that the Court of Appeals can reconsider,
under the proper standard, whether the relevant claims in
the ’753 patent are sufficiently definite. See, e.g., Johnson
v. California, 

, 515 (2005); Gasperini v. Cen-
ter for Humanities, Inc., 

, 438 (1996).
                       *   *      *
  For the reasons stated, we vacate the judgment of the
United States Court of Appeals for the Federal Circuit and
remand the case for further proceedings consistent with
this opinion.
                                           It is so ordered.




——————
 11 Notably, however, all three panel members found Nautilus’ argu­

ments unavailing.
                Cite as: 572 U. S. ____ (2014)   15

                   Opinion of the Court
              Appendix to opinion of the Court


                       APPENDIX




Patent No. 5,337,753, Figure 1