(Slip Opinion)              OCTOBER TERM, 2014                                       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

                    HEIEN v. NORTH CAROLINA

 CERTIORARI TO THE SUPREME COURT OF NORTH CAROLINA

  No. 13–604.      Argued October 6, 2014—Decided December 15, 2014
Following a suspicious vehicle, Sergeant Matt Darisse noticed that only
  one of the vehicle’s brake lights was working and pulled the driver
  over. While issuing a warning ticket for the broken brake light, Dar-
  isse became suspicious of the actions of the two occupants and their
  answers to his questions. Petitioner Nicholas Brady Heien, the car’s
  owner, gave Darisse consent to search the vehicle. Darisse found co-
  caine, and Heien was arrested and charged with attempted traffick-
  ing. The trial court denied Heien’s motion to suppress the seized evi-
  dence on Fourth Amendment grounds, concluding that the vehicle’s
  faulty brake light gave Darisse reasonable suspicion to initiate the
  stop. The North Carolina Court of Appeals reversed, holding that the
  relevant code provision, which requires that a car be “equipped with
  a stop lamp,” N. C. Gen. Stat. Ann. §20–129(g), requires only a single
  lamp—which Heien’s vehicle had—and therefore the justification for
  the stop was objectively unreasonable. Reversing in turn, the State
  Supreme Court held that, even assuming no violation of the state law
  had occurred, Darisse’s mistaken understanding of the law was rea-
  sonable, and thus the stop was valid.
Held: Because Darisse’s mistake of law was reasonable, there was rea-
 sonable suspicion justifying the stop under the Fourth Amendment.
 Pp. 4–13.
    (a) The Fourth Amendment requires government officials to act
 reasonably, not perfectly, and gives those officials “fair leeway for en-
 forcing the law,” Brinegar v. United States, 

, 176.
 Searches and seizures based on mistakes of fact may be reasonable.
 See, e.g., Illinois v. Rodriguez, 

, 183–186. The limiting
 factor is that “the mistakes must be those of reasonable men.”
 

. Mistakes of law are no less compatible with
 the concept of reasonable suspicion, which arises from an under-
2                      HEIEN v. NORTH CAROLINA

                                   Syllabus

    standing of both the facts and the relevant law. Whether an officer is
    reasonably mistaken about the one or the other, the result is the
    same: the facts are outside the scope of the law. And neither the
    Fourth Amendment’s text nor this Court’s precedents offer any rea-
    son why that result should not be acceptable when reached by a rea-
    sonable mistake of law.
       More than two centuries ago, this Court held that reasonable mis-
    takes of law, like those of fact, could justify a certificate of probable
    cause. United States v. Riddle, 5 Cranch 311, 313. That holding was
    reiterated in numerous 19th-century decisions. Although Riddle was
    not a Fourth Amendment case, it explained the concept of probable
    cause, which this Court has said carried the same “fixed and well
    known meaning” in the Fourth Amendment, 

,
    and n. 14, and no subsequent decision of this Court has undermined
    that understanding. The contrary conclusion would be hard to recon-
    cile with the more recent precedent of Michigan v. DeFillippo, 

, where the Court, addressing the validity of an arrest made
    under a criminal law later declared unconstitutional, held that the of-
    ficers’ reasonable assumption that the law was valid gave them
    “abundant probable cause” to make the arrest, 

Heien at-
    tempts to recast DeFillippo as a case solely about the exclusionary
    rule, not the Fourth Amendment itself, but DeFillippo’s express hold-
    ing is that the arrest was constitutionally valid because the officers
    had probable cause. See 

Heien misplaces his reliance on
    cases such as Davis v. United States, 564 U. S. ___, where any con-
    sideration of reasonableness was limited to the separate matter of
    remedy, not whether there was a Fourth Amendment violation in the
    first place.
       Heien contends that the rationale that permits reasonable errors of
    fact does not extend to reasonable errors of law, arguing that officers
    in the field deserve a margin of error when making factual assess-
    ments on the fly. An officer may, however, also be suddenly confront-
    ed with a situation requiring application of an unclear statute. This
    Court’s holding does not discourage officers from learning the law.
    Because the Fourth Amendment tolerates only objectively reasonable
    mistakes, cf. Whren v. United States, 

, 813, an officer
    can gain no advantage through poor study. Finally, while the maxim
    “Ignorance of the law is no excuse” correctly implies that the State
    cannot impose punishment based on a mistake of law, it does not
    mean a reasonable mistake of law cannot justify an investigatory
    stop. Pp. 4–12.
       (b) There is little difficulty in concluding that Officer Darisse’s er-
    ror of law was reasonable. The North Carolina vehicle code that re-
    quires “a stop lamp” also provides that the lamp “may be incorpo-
                     Cite as: 574 U. S. ____ (2014)                   3

                                Syllabus

  rated into a unit with one or more other rear lamps,” N. C. Gen. Stat.
  Ann. §20–129(g), and that “all originally equipped rear lamps” must
  be “in good working order,” §20–129(d). Although the State Court of
  Appeals held that “rear lamps” do not include brake lights, the word
  “other,” coupled with the lack of state-court precedent interpreting
  the provision, made it objectively reasonable to think that a faulty
  brake light constituted a violation. Pp. 12–13.
367 N. C. 163, 

, affirmed.

  ROBERTS, C. J., delivered the opinion of the Court, in which SCALIA,
KENNEDY, THOMAS, GINSBURG, BREYER, ALITO, and KAGAN, JJ., joined.
KAGAN, J., filed a concurring opinion, in which GINSBURG, J., joined.
SOTOMAYOR, J., filed a dissenting opinion.
                        Cite as: 574 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. 13–604
                                   _________________


 NICHOLAS BRADY HEIEN, PETITIONER v. NORTH 

                CAROLINA

ON WRIT OF CERTIORARI TO THE SUPREME COURT OF NORTH
                      CAROLINA
                              [December 15, 2014]

  CHIEF JUSTICE ROBERTS delivered the opinion of the
Court.
  The Fourth Amendment prohibits “unreasonable
searches and seizures.” Under this standard, a search or
seizure may be permissible even though the justification
for the action includes a reasonable factual mistake. An
officer might, for example, stop a motorist for traveling
alone in a high-occupancy vehicle lane, only to discover
upon approaching the car that two children are slumped
over asleep in the back seat. The driver has not violated
the law, but neither has the officer violated the Fourth
Amendment.
  But what if the police officer’s reasonable mistake is not
one of fact but of law? In this case, an officer stopped a
vehicle because one of its two brake lights was out, but a
court later determined that a single working brake light
was all the law required. The question presented is
whether such a mistake of law can nonetheless give rise to
the reasonable suspicion necessary to uphold the seizure
under the Fourth Amendment. We hold that it can. Be-
cause the officer’s mistake about the brake-light law was
2                HEIEN v. NORTH CAROLINA

                     Opinion of the Court

reasonable, the stop in this case was lawful under the
Fourth Amendment.
                              I
   On the morning of April 29, 2009, Sergeant Matt Da-
risse of the Surry County Sheriff ’s Department sat in his
patrol car near Dobson, North Carolina, observing north-
bound traffic on Interstate 77. Shortly before 8 a.m., a
Ford Escort passed by. Darisse thought the driver looked
“very stiff and nervous,” so he pulled onto the interstate
and began following the Escort. A few miles down the
road, the Escort braked as it approached a slower vehicle,
but only the left brake light came on. Noting the faulty
right brake light, Darisse activated his vehicle’s lights and
pulled the Escort over. App. 4–7, 15–16.
   Two men were in the car: Maynor Javier Vasquez sat
behind the wheel, and petitioner Nicholas Brady Heien lay
across the rear seat. Sergeant Darisse explained to
Vasquez that as long as his license and registration
checked out, he would receive only a warning ticket for the
broken brake light. A records check revealed no problems
with the documents, and Darisse gave Vasquez the warn-
ing ticket. But Darisse had become suspicious during the
course of the stop—Vasquez appeared nervous, Heien
remained lying down the entire time, and the two gave
inconsistent answers about their destination. Darisse
asked Vasquez if he would be willing to answer some
questions. Vasquez assented, and Darisse asked whether
the men were transporting various types of contraband.
Told no, Darisse asked whether he could search the Es-
cort. Vasquez said he had no objection, but told Darisse he
should ask Heien, because Heien owned the car. Heien
gave his consent, and Darisse, aided by a fellow officer
who had since arrived, began a thorough search of the
vehicle. In the side compartment of a duffle bag, Darisse
found a sandwich bag containing cocaine. The officers
                 Cite as: 574 U. S. ____ (2014)            3

                     Opinion of the Court

arrested both men. 366 N. C. 271, 272–273, 

, 352–353 (2012); App. 5–6, 25, 37.
   The State charged Heien with attempted trafficking in
cocaine. Heien moved to suppress the evidence seized
from the car, contending that the stop and search had
violated the Fourth Amendment of the United States
Constitution. After a hearing at which both officers testi-
fied and the State played a video recording of the stop, the
trial court denied the suppression motion, concluding that
the faulty brake light had given Sergeant Darisse reason-
able suspicion to initiate the stop, and that Heien’s subse-
quent consent to the search was valid. Heien pleaded
guilty but reserved his right to appeal the suppression
decision. App. 1, 7–10, 12, 29, 43–44.
   The North Carolina Court of Appeals reversed. 214
N. C. App. 515, 

(2011). The initial stop
was not valid, the court held, because driving with only
one working brake light was not actually a violation of
North Carolina law. The relevant provision of the vehicle
code provides that a car must be
    “equipped with a stop lamp on the rear of the vehicle.
    The stop lamp shall display a red or amber light visi-
    ble from a distance of not less than 100 feet to the
    rear in normal sunlight, and shall be actuated upon
    application of the service (foot) brake. The stop lamp
    may be incorporated into a unit with one or more
    other rear lamps.” N. C. Gen. Stat. Ann. §20–129(g)
    (2007).
   Focusing on the statute’s references to “a stop lamp” and
“[t]he stop lamp” in the singular, the court concluded that
a vehicle is required to have only one working brake
light—which Heien’s vehicle indisputably did. The justifi-
cation for the stop was therefore “objectively unreason-
able,” and the stop violated the Fourth Amendment. 214
N. C. App., at 

–831.
4                HEIEN v. NORTH CAROLINA

                     Opinion of the Court

   The State appealed, and the North Carolina Supreme
Court reversed. 366 N. C. 271, 

. Noting
that the State had chosen not to seek review of the Court
of Appeals’ interpretation of the vehicle code, the North
Carolina Supreme Court assumed for purposes of its
decision that the faulty brake light was not a violation.

, at 354. But the court concluded
that, for several reasons, Sergeant Darisse could have
reasonably, even if mistakenly, read the vehicle code to
require that both brake lights be in good working order.
Most notably, a nearby code provision requires that “all
originally equipped rear lamps” be functional. 

–359 (quoting N. C. Gen. Stat.
Ann. §20–129(d)). Because Sergeant Darisse’s mistaken
understanding of the vehicle code was reasonable, the stop
was valid. “An officer may make a mistake, including a
mistake of law, yet still act reasonably under the circum-
stances. . . . [W]hen an officer acts reasonably under the
circumstances, he is not violating the Fourth Amend-
ment.” 

, at 356.
   The North Carolina Supreme Court remanded to the
Court of Appeals to address Heien’s other arguments for
suppression (which are not at issue here). 

, at 359. The Court of Appeals rejected those
arguments and affirmed the trial court’s denial of his
motion to suppress. ___ N. C. App. ___, 

(2013). The North Carolina Supreme Court affirmed in
turn. 367 N. C. 163, 

(2013). We granted
certiorari. 572 U. S. ___ (2014).
                          II
    The Fourth Amendment provides:
       “The right of the people to be secure in their per-
     sons, houses, papers, and effects, against unreason-
     able searches and seizures, shall not be violated, and
     no Warrants shall issue, but upon probable cause,
                  Cite as: 574 U. S. ____ (2014)            5

                      Opinion of the Court

    supported by Oath or affirmation, and particularly
    describing the place to be searched, and the persons or
    things to be seized.”
   A traffic stop for a suspected violation of law is a “sei-
zure” of the occupants of the vehicle and therefore must be
conducted in accordance with the Fourth Amendment.
Brendlin v. California, 

, 255–259 (2007). All
parties agree that to justify this type of seizure, officers
need only “reasonable suspicion”—that is, “a particular-
ized and objective basis for suspecting the particular
person stopped” of breaking the law. Prado Navarette v.
California, 572 U. S. ___, ___ (2014) (slip op., at 3) (inter-
nal quotation marks omitted). The question here is
whether reasonable suspicion can rest on a mistaken
understanding of the scope of a legal prohibition. We hold
that it can.
   As the text indicates and we have repeatedly affirmed,
“the ultimate touchstone of the Fourth Amendment is
‘reasonableness.’ ” Riley v. California, 573 U. S. ___, ___
(2014) (slip op., at 5) (some internal quotation marks
omitted). To be reasonable is not to be perfect, and so the
Fourth Amendment allows for some mistakes on the part
of government officials, giving them “fair leeway for en-
forcing the law in the community’s protection.” Brinegar
v. United States, 

, 176 (1949). We have
recognized that searches and seizures based on mistakes
of fact can be reasonable. The warrantless search of a
home, for instance, is reasonable if undertaken with the
consent of a resident, and remains lawful when officers
obtain the consent of someone who reasonably appears to
be but is not in fact a resident. See Illinois v. Rodriguez,

, 183–186 (1990). By the same token, if
officers with probable cause to arrest a suspect mistakenly
arrest an individual matching the suspect’s description,
neither the seizure nor an accompanying search of the
6               HEIEN v. NORTH CAROLINA

                     Opinion of the Court

arrestee would be unlawful. See Hill v. California, 

, 802–805 (1971). The limit is that “the mistakes
must be those of reasonable men.” 

.
  But reasonable men make mistakes of law, too, and such
mistakes are no less compatible with the concept of rea-
sonable suspicion. Reasonable suspicion arises from the
combination of an officer’s understanding of the facts and
his understanding of the relevant law. The officer may be
reasonably mistaken on either ground. Whether the facts
turn out to be not what was thought, or the law turns out
to be not what was thought, the result is the same: the
facts are outside the scope of the law. There is no reason,
under the text of the Fourth Amendment or our prece-
dents, why this same result should be acceptable when
reached by way of a reasonable mistake of fact, but not
when reached by way of a similarly reasonable mistake of
law.
  The dissent counters that our cases discussing probable
cause and reasonable suspicion, most notably Ornelas v.
United States, 

, 696–697 (1996), have con-
tained “scarcely a peep” about mistakes of law. Post, at 2–3
(opinion of SOTOMAYOR, J.). It would have been surpris-
ing, of course, if they had, since none of those cases in-
volved a mistake of law.
  Although such recent cases did not address mistakes of
law, older precedents did. In fact, cases dating back two
centuries support treating legal and factual errors alike in
this context. Customs statutes enacted by Congress not
long after the founding authorized courts to issue certifi-
cates indemnifying customs officers against damages suits
premised on unlawful seizures. See, e.g., Act of Mar. 2,
1799, ch. 22, §89, 1 Stat. 695–696. Courts were to issue
such certificates on a showing that the officer had “rea-
sonable cause”—a synonym for “probable cause”—for the
challenged seizure. Ibid.; see Stacey v. Emery, 97 U. S.
                 Cite as: 574 U. S. ____ (2014)           7

                     Opinion of the Court

642, 646 (1878); United States v. Riddle, 5 Cranch 311
(1809). In United States v. Riddle, a customs officer seized
goods on the ground that the English shipper had violated
the customs laws by preparing an invoice that underval-
ued the merchandise, even though the American consignee
declared the true value to the customs collector. Chief
Justice Marshall held that there had been no violation of
the customs law because, whatever the shipper’s inten-
tion, the consignee had not actually attempted to defraud
the Government. Nevertheless, because “the construction
of the law was liable to some question,” he affirmed the
issuance of a certificate of probable cause: “A doubt as to
the true construction of the law is as reasonable a cause
for seizure as a doubt respecting the fact.” 

   This holding—that reasonable mistakes of law, like
those of fact, would justify certificates of probable cause—
was reiterated in a number of 19th-century decisions. See,
e.g., The Friendship, 

, 826 (No. 5,125) (CC
Mass. 1812) (Story, J.); United States v. The Reindeer, 

, 768 (No. 16,145) (CC RI 1848); United States
v. The Recorder, 

(No. 16,130) (CC SDNY
1849). By the Civil War, there had been “numerous cases
in which [a] captured vessel was in no fault, and had not,
under a true construction of the law, presented even
ground of suspicion, and yet the captor was exonerated
because he acted under an honest mistake of the law.”
The La Manche, 

, 972 (No. 8,004) (D Mass.
1863).
   Riddle and its progeny are not directly on point. Chief
Justice Marshall was not construing the Fourth Amend-
ment, and a certificate of probable cause functioned much
like a modern-day finding of qualified immunity, which
depends on an inquiry distinct from whether an officer has
committed a constitutional violation. See, e.g., Carroll v.
Carman, ante, at 7 (per curiam). But Chief Justice Mar-
shall was nevertheless explaining the concept of probable
8                    HEIEN v. NORTH CAROLINA

                          Opinion of the Court

cause, which, he noted elsewhere, “in all cases of seizure,
has a fixed and well known meaning. It imports a seizure
made under circumstances which warrant suspicion.”
Locke v. United States, 7 Cranch 339, 348 (1813). We have
said the phrase “probable cause” bore this “fixed and well
known meaning” in the Fourth Amendment, see 

, and n. 14, and Riddle illustrates that it
encompassed suspicion based on reasonable mistakes of
both fact and law. No decision of this Court in the two
centuries since has undermined that understanding.*
   The contrary conclusion would be hard to reconcile with
a much more recent precedent. In Michigan v. DeFillippo,

(1979), we addressed the validity of an arrest
made under a criminal law later declared unconstitu-
tional. A Detroit ordinance that authorized police officers
to stop and question individuals suspected of criminal activ-
ity also made it an offense for such an individual “to refuse
to identify himself and produce evidence of his identity.”

Detroit police officers sent to investigate a
report of public intoxication arrested Gary DeFillippo after
he failed to identify himself. A search incident to arrest
uncovered drugs, and DeFillippo was charged with posses-
sion of a controlled substance. The Michigan Court of
Appeals ordered the suppression of the drugs, concluding
that the identification ordinance was unconstitutionally
vague and that DeFillippo’s arrest was therefore invalid.

——————
   * The dissent contends that “the tolerance of mistakes of law in cases
like Riddle was a result of the specific customs statute that Congress
had enacted.” Post, at 8, n. 3 (citing The Apollon, 

, 373
(1824) (Story, J.)). The relevant portion of The Apollon, however,
addressed “the effect of probable cause,” not what gave rise to it. 

(emphasis added); see 

(finding it “unnecessary” to decide
whether probable cause existed because it “would not, under the
circumstances of this case, constitute a valid defence”). Justice Story
understandably did not cite Riddle or discuss its tolerance of mistakes
of law anywhere in The Apollon.
                 Cite as: 574 U. S. ____ (2014)            9

                     Opinion of the Court

   Accepting the unconstitutionality of the ordinance as a
given, we nonetheless reversed. At the time the officers
arrested DeFillippo, we explained, “there was no control-
ling precedent that this ordinance was or was not consti-
tutional, and hence the conduct observed violated a pre-
sumptively valid ordinance.” 

Acknowledging
that the outcome might have been different had the ordi-
nance been “grossly and flagrantly unconstitutional,” we
concluded that under the circumstances “there was abun-
dant probable cause to satisfy the constitutional prerequi-
site for an arrest.” 

   The officers were wrong in concluding that DeFillippo
was guilty of a criminal offense when he declined to iden-
tify himself. That a court only later declared the ordinance
unconstitutional does not change the fact that DeFillippo’s
conduct was lawful when the officers observed it. See
Danforth v. Minnesota, 

, 271 (2008). But the
officers’ assumption that the law was valid was reason-
able, and their observations gave them “abundant probable
cause” to arrest 

. Although
DeFillippo could not be prosecuted under the identifica-
tion ordinance, the search that turned up the drugs was
constitutional.
   Heien struggles to recast DeFillippo as a case solely
about the exclusionary rule, not the Fourth Amendment
itself. In his view, the officers’ mistake of law resulted in
a violation the Fourth Amendment, but suppression of the
drugs was not the proper remedy. We did say in a footnote
that suppression of the evidence found on DeFillippo
would serve none of the purposes of the exclusionary rule.
See 

n. 3. But that literally marginal discussion
does not displace our express holding that the arrest was
constitutionally valid because the officers had probable
cause. See 

Nor, contrary to Heien’s suggestion,
did either United States v. Leon, 

(1984), or
Illinois v. Gates, 

(1983), somehow erase that
10               HEIEN v. NORTH CAROLINA

                      Opinion of the Court

holding and transform DeFillippo into an exclusionary
rule decision. See Brief for Petitioner 28–29. In Leon, we
said DeFillippo paid “attention to the purposes underlying
the exclusionary rule,” but we also clarified that it did “not
involv[e] the scope of the rule 

–
912. As for Gates, only Justice White’s separate opinion
(joined by no other Justice) discussed DeFillippo, and it
acknowledged that “DeFillippo did not modify the exclu-
sionary rule itself ” but instead “upheld the validity of an

, n. 12 (opinion concurring in
judgment).
   Heien is correct that in a number of decisions we have
looked to the reasonableness of an officer’s legal error in
the course of considering the appropriate remedy for a
constitutional violation, instead of whether there was a
violation at all. See, e.g., Davis v. United States, 564 U. S.
___, ___ (2011) (slip op., at 11) (exclusionary rule); Illinois
v. Krull, 

, 359–360 (1987) (exclusionary rule);
Wilson v. Layne, 

, 615 (1999) (qualified im-
munity); Anderson v. Creighton, 

, 641 (1987)
(qualified immunity). In those cases, however, we had
already found or assumed a Fourth Amendment violation.
An officer’s mistaken view that the conduct at issue did
not give rise to such a violation—no matter how reason-
able—could not change that ultimate conclusion. See Brief
for Respondent 29–31; Brief for United States as Amicus
Curiae 30, n. 3. Any consideration of the reasonableness
of an officer’s mistake was therefore limited to the sepa-
rate matter of remedy.
   Here, by contrast, the mistake of law relates to the
antecedent question of whether it was reasonable for an
officer to suspect that the defendant’s conduct was illegal.
If so, there was no violation of the Fourth Amendment in
the first place. None of the cases Heien or the dissent
cites precludes a court from considering a reasonable
mistake of law in addressing that question. Cf. Herring v.
                  Cite as: 574 U. S. ____ (2014)           11

                      Opinion of the Court

United States, 

, 139 (2009) (assuming a
Fourth Amendment violation while rejecting application of
the exclusionary rule, but noting that “[w]hen a probable-
cause determination was based on reasonable but mis-
taken assumptions, the person subjected to a search or
seizure has not necessarily been the victim of a constitu-
tional violation”).
   Heien also contends that the reasons the Fourth
Amendment allows some errors of fact do not extend to
errors of law. Officers in the field must make factual
assessments on the fly, Heien notes, and so deserve a
margin of error. In Heien’s view, no such margin is ap-
propriate for questions of law: The statute here either
requires one working brake light or two, and the answer
does not turn on anything “an officer might suddenly
confront in the field.” Brief for Petitioner 21. But Heien’s
point does not consider the reality that an officer may
“suddenly confront” a situation in the field as to which the
application of a statute is unclear—however clear it may
later become. A law prohibiting “vehicles” in the park
either covers Segways or not, see A. Scalia & B. Garner,
Reading Law: The Interpretation of Legal Texts 36–38
(2012), but an officer will nevertheless have to make a
quick decision on the law the first time one whizzes by.
   Contrary to the suggestion of Heien and amici, our
decision does not discourage officers from learning the
law. The Fourth Amendment tolerates only reasonable
mistakes, and those mistakes—whether of fact or of law—
must be objectively reasonable. We do not examine the
subjective understanding of the particular officer involved.
Cf. Whren v. United States, 

, 813 (1996). And
the inquiry is not as forgiving as the one employed in the
distinct context of deciding whether an officer is entitled to
qualified immunity for a constitutional or statutory viola-
tion. Thus, an officer can gain no Fourth Amendment
advantage through a sloppy study of the laws he is duty-
12              HEIEN v. NORTH CAROLINA

                     Opinion of the Court

bound to enforce.
   Finally, Heien and amici point to the well-known maxim,
“Ignorance of the law is no excuse,” and contend that it
is fundamentally unfair to let police officers get away with
mistakes of law when the citizenry is accorded no such
leeway. Though this argument has a certain rhetorical
appeal, it misconceives the implication of the maxim. The
true symmetry is this: Just as an individual generally
cannot escape criminal liability based on a mistaken
understanding of the law, so too the government cannot
impose criminal liability based on a mistaken understand-
ing of the law. If the law required two working brake
lights, Heien could not escape a ticket by claiming he
reasonably thought he needed only one; if the law required
only one, Sergeant Darisse could not issue a valid ticket by
claiming he reasonably thought drivers needed two. But
just because mistakes of law cannot justify either the
imposition or the avoidance of criminal liability, it does
not follow that they cannot justify an investigatory stop.
And Heien is not appealing a brake-light ticket; he is
appealing a cocaine-trafficking conviction as to which
there is no asserted mistake of fact or law.
                            III
   Here we have little difficulty concluding that the of-
ficer’s error of law was reasonable. Although the North
Carolina statute at issue refers to “a stop lamp,” suggest-
ing the need for only a single working brake light, it also
provides that “[t]he stop lamp may be incorporated into a
unit with one or more other rear lamps.” N. C. Gen. Stat.
Ann. §20–129(g) (emphasis added). The use of “other”
suggests to the everyday reader of English that a “stop
lamp” is a type of “rear lamp.” And another subsection of
the same provision requires that vehicles “have all origi-
nally equipped rear lamps or the equivalent in good work-
ing order,” §20–129(d), arguably indicating that if a vehi-
                 Cite as: 574 U. S. ____ (2014)          13

                     Opinion of the Court

cle has multiple “stop lamp[s],” all must be functional.
   The North Carolina Court of Appeals concluded that the
“rear lamps” discussed in subsection (d) do not include
brake lights, but, given the “other,” it would at least have
been reasonable to think they did. Both the majority and
the dissent in the North Carolina Supreme Court so con-
cluded, and we agree. See 366 N. C., at 282–283, 

, at 358–359; id., at 

(Hudson,
J., dissenting) (calling the Court of Appeals’ decision
“surprising”). This “stop lamp” provision, moreover, had
never been previously construed by North Carolina’s
appellate courts. See id., at 

(majority opinion). It was thus objectively reasonable for
an officer in Sergeant Darisse’s position to think that
Heien’s faulty right brake light was a violation of North
Carolina law. And because the mistake of law was rea-
sonable, there was reasonable suspicion justifying the
stop.
   The judgment of the Supreme Court of North Carolina is
                                                   Affirmed.
                      Cite as: 574 U. S. ____ (2014)                     1

                          KAGAN, J., concurring

SUPREME COURT OF THE UNITED STATES
                               _________________

                               No. 13–604
                               _________________


  NICHOLAS BRADY HEIEN, PETITIONER v. NORTH 

                 CAROLINA

ON WRIT OF CERTIORARI TO THE SUPREME COURT OF NORTH
                      CAROLINA
                          [December 15, 2014]

   JUSTICE KAGAN, with whom JUSTICE GINSBURG joins,
concurring.
   I concur in full in the Court’s opinion, which explains
why certain mistakes of law can support the reasonable
suspicion needed to stop a vehicle under the Fourth
Amendment. In doing so, the Court correctly emphasizes
that the “Fourth Amendment tolerates only . . . objectively
reasonable” mistakes of law. Ante, at 11. And the Court
makes clear that the inquiry into whether an officer’s
mistake of law counts as objectively reasonable “is not as
forgiving as the one employed in the distinct context of
deciding whether an officer is entitled to qualified immun-
ity.” 

to elaborate briefly on those
important limitations.1
   First, an officer’s “subjective understanding” is irrele-
vant: As the Court notes, “[w]e do not examine” it at all.
——————
   1 I note in addition, as does the Court, that one kind of mistaken legal

judgment—an error about the contours of the Fourth Amendment
itself—can never support a search or seizure. See ante, at 10 (“An
officer’s mistaken view that” conduct does “not give rise to” a Fourth
Amendment violation, “no matter how reasonable,” cannot change a
court’s “ultimate conclusion” that such a violation has occurred). As the
Solicitor General has explained, mistakes about the requirements of
the Fourth Amendment “violate the Fourth Amendment even when
they are reasonable.” Brief for United States as Amicus Curiae 30, n. 3;
see Brief for Respondent 29 (stating the same view).
2               HEIEN v. NORTH CAROLINA

                    KAGAN, J., concurring

government cannot defend an of-
ficer’s mistaken legal interpretation on the ground that
the officer was unaware of or untrained in the law. And it
means that, contrary to the dissenting opinion in the court
below, an officer’s reliance on “an incorrect memo or train-
ing program from the police department” makes no differ-
ence to the analysis. 366 N. C. 271, 284, 

,
360 (2012) (Hudson, J., dissenting). Those considerations
pertain to the officer’s subjective understanding of the law
and thus cannot help to justify a seizure.
   Second, the inquiry the Court permits today is more
demanding than the one courts undertake before awarding
qualified immunity. See Tr. of Oral Arg. 51 (Solicitor
General stating that the two tests “require essentially the
opposite” showings); Brief for Respondent 31–32 (making
a similar point). Our modern qualified immunity doctrine
protects “all but the plainly incompetent or those who
knowingly violate the law.” Ashcroft v. al-Kidd, 563 U. S.
___, ___ (2011) (slip op., at 12) (quoting Malley v. Briggs,

, 341 (1986)). By contrast, Justice Story’s
opinion in The Friendship, 

, 826 (No. 5,125)
(CC Mass. 1812) (cited ante, at 7), suggests the appropri-
ate standard for deciding when a legal error can support a
seizure: when an officer takes a reasonable view of a “vex-
ata questio” on which different judges “h[o]ld opposite
opinions.” See Brief for United States as Amicus Curiae
26 (invoking that language). Or to make the same point
without the Latin, the test is satisfied when the law at
issue is “so doubtful in construction” that a reasonable
judge could agree with the officer’s view. The 

.
   A court tasked with deciding whether an officer’s mis-
take of law can support a seizure thus faces a straightfor-
ward question of statutory construction. If the statute is
genuinely ambiguous, such that overturning the officer’s
judgment requires hard interpretive work, then the officer
                 Cite as: 574 U. S. ____ (2014)            3

                     KAGAN, J., concurring

has made a reasonable mistake. But if not, not. As the
Solicitor General made the point at oral argument, the
statute must pose a “really difficult” or “very hard ques-
tion of statutory interpretation.” Tr. of Oral Arg. 50. And
indeed, both North Carolina and the Solicitor General
agreed that such cases will be “exceedingly rare.” Brief for
Respondent 17; Tr. of Oral Arg. 48.
   The Court’s analysis of Sergeant Darisse’s interpreta-
tion of the North Carolina law at issue here appropriately
reflects these principles. As the Court explains, see ante,
at 12–13, the statute requires every car on the highway to
have “a stop lamp,” in the singular. N. C. Gen. Stat. Ann.
§20–129(g) (2007). But the statute goes on to state that a
stop lamp (or, in more modern terminology, brake light)
“may be incorporated into a unit with one or more other
rear lamps,” suggesting that a stop lamp itself qualifies as
a rear lamp. 

the statute
further mandates that every car have “all originally
equipped rear lamps . . . in good working order.” §20–
129(d) (emphasis added). The North Carolina Court of
Appeals dealt with the statute’s conflicting signals in one
way (deciding that a brake light is not a rear lamp, and so
only one needs to work); but a court could easily take the
officer’s view (deciding that a brake light is a rear lamp,
and if a car comes equipped with more than one, as mod-
ern cars do, all must be in working order). The critical
point is that the statute poses a quite difficult question of
interpretation, and Sergeant Darisse’s judgment, although
overturned, had much to recommend it. I therefore agree
with the Court that the traffic stop he conducted did not
violate the Fourth Amendment.
                  Cite as: 574 U. S. ____ (2014)             1

                    SOTOMAYOR, J., dissenting

SUPREME COURT OF THE UNITED STATES
                          _________________

                           No. 13–604
                          _________________


 NICHOLAS BRADY HEIEN, PETITIONER v. NORTH 

                CAROLINA

ON WRIT OF CERTIORARI TO THE SUPREME COURT OF NORTH
                      CAROLINA
                      [December 15, 2014]

  JUSTICE SOTOMAYOR, dissenting.
  The Court is, of course, correct that “ ‘the ultimate
touchstone of the Fourth Amendment is “reasonable-
ness.” ’ ” Riley v. California, 573 U. S. ___, ___ (2014) (slip
op., at 5). But this broad statement simply sets the stand-
ard a court is to apply when it conducts its inquiry into
whether the Fourth Amendment has been violated. It
does not define the categories of inputs that courts are to
consider when assessing the reasonableness of a search or
seizure, each of which must be independently justified.
What this case requires us to decide is whether a police
officer’s understanding of the law is an input into the
reasonableness inquiry, or whether this inquiry instead
takes the law as a given and assesses an officer’s under-
standing of the facts against a fixed legal yardstick.
  I would hold that determining whether a search or
seizure is reasonable requires evaluating an officer’s un-
derstanding of the facts against the actual state of the law.
I would accordingly reverse the judgment of the North
Carolina Supreme Court, and I respectfully dissent from
the Court’s contrary holding.
                         I
 It is common ground that Heien was seized within the
meaning of the Fourth Amendment. Such a seizure com-
2                HEIEN v. NORTH CAROLINA

                   SOTOMAYOR, J., dissenting

ports with the Constitution only if the officers had articu-
lable and reasonable suspicion that Heien was breaking
the law. In Ornelas v. United States, 

, 696
(1996), we explained that the “principal components” of
that determination “will be the events which occurred
leading up to the stop or search, and then the decision
whether these historical facts, viewed from the standpoint
of an objectively reasonable police officer, amount to rea-
sonable suspicion or to probable cause.” We described this
kind of determination as “a mixed question of law and
fact”: “ ‘[T]he issue is whether the facts satisfy the [rele-
vant] statutory [or constitutional] standard, or to put it
another way, whether the rule of law as applied to the
established facts is or is not violated.’ ” 

(quoting Pullman-Standard v. Swint, 456 U. S 273, 289,
n. 19 (1982)). What matters, we said, are the facts as
viewed by an objectively reasonable officer, and the rule of
law—not an officer’s conception of the rule of law, and not
even an officer’s reasonable misunderstanding about the
law, but the law.
   As a result, when we have talked about the leeway that
officers have in making probable-cause determinations, we
have focused on their assessments of facts. See, e.g., Terry
v. Ohio, 

, 21–22 (1968) (framing the question as
whether the “facts” give rise to reasonable suspicion). We
have conceded that an arresting officer’s state of mind
does not factor into the probable-cause inquiry, “except for
the facts that he knows.” Devenpeck v. Alford, 

, 153 (2004) (emphasis added). And we have said that,
to satisfy the reasonableness requirement, “what is gener-
ally demanded of the many factual determinations that
must regularly be made by agents of the government . . . is
not that they always be correct, but that they always be
reasonable.” Illinois v. Rodriguez, 

, 185
(1990) (emphasis added). There is scarcely a peep in these
cases to suggest that an officer’s understanding or concep-
                 Cite as: 574 U. S. ____ (2014)            3

                   SOTOMAYOR, J., dissenting

tion of anything other than the facts is relevant.
   This framing of the reasonableness inquiry has not only
been focused on officers’ understanding of the facts, it has
been justified in large part based on the recognition that
officers are generally in a superior position, relative to
courts, to evaluate those facts and their significance as
they unfold. In other words, the leeway we afford officers’
factual assessments is rooted not only in our recognition
that police officers operating in the field have to make
quick decisions, see 

but also in our understand-
ing that police officers have the expertise to “dra[w] infer-
ences and mak[e] deductions . . . that might well elude an
untrained person.” United States v. Cortez, 

,
418 (1981). When officers evaluate unfolding circum-
stances, they deploy that expertise to draw “conclusions
about human behavior” much in the way that “jurors [do]
as factfinders.” 

same cannot be said about legal exegesis. After all,
the meaning of the law is not probabilistic in the same
way that factual determinations are. Rather, “the notion
that the law is definite and knowable” sits at the founda-
tion of our legal system. Cheek v. United States, 

, 199 (1991). And it is courts, not officers, that are in
the best position to interpret the laws.
   Both our enunciation of the reasonableness inquiry and
our justification for it thus have always turned on an
officer’s factual conclusions and an officer’s expertise with
respect to those factual conclusions. Neither has hinted at
taking into account an officer’s understanding of the law,
reasonable or otherwise.
                             II
  Departing from this tradition means further eroding the
Fourth Amendment’s protection of civil liberties in a
context where that protection has already been worn
down. Traffic stops like those at issue here can be “annoy-
4                HEIEN v. NORTH CAROLINA

                   SOTOMAYOR, J., dissenting

ing, frightening, and perhaps humiliating.” 

; see Delaware v. Prouse, 

, 657
(1979). We have nevertheless held that an officer’s subjec-
tive motivations do not render a traffic stop unlawful.
Whren v. United States, 

(1996). But we
assumed in Whren that when an officer acts on pretext, at
least that pretext would be the violation of an actual law.
See 

(discussing the three provisions of the
District of Columbia traffic code that the parties accepted
the officer had probable cause to believe had been vio-
lated). Giving officers license to effect seizures so long as
they can attach to their reasonable view of the facts some
reasonable legal interpretation (or misinterpretation) that
suggests a law has been violated significantly expands this
authority. Cf. Barlow v. United States, 

, 411
(1833) (Story, J.) (“There is scarcely any law which does
not admit of some ingenious doubt”). One wonders how a
citizen seeking to be law-abiding and to structure his or
her behavior to avoid these invasive, frightening, and
humiliating encounters could do so.
   In addition to these human consequences—including
those for communities and for their relationships with the
police—permitting mistakes of law to justify seizures has
the perverse effect of preventing or delaying the clarifica-
tion of the law. Under such an approach, courts need not
interpret statutory language but can instead simply decide
whether an officer’s interpretation was reasonable. In-
deed, had this very case arisen after the North Carolina
Supreme Court announced its rule, the North Carolina
Court of Appeals would not have had the occasion to in-
terpret the statute at issue. Similarly, courts in the
Eighth Circuit, which has been the only Circuit to include
police mistakes of law in the reasonableness inquiry, have
observed that they need not decide interpretive questions
under their approach. See, e.g., United States v. Rodriguez-
                     Cite as: 574 U. S. ____ (2014)                   5

                      SOTOMAYOR, J., dissenting

Lopez, 

, 1022–1023 (CA8 2006).1 This
result is bad for citizens, who need to know their rights
and responsibilities, and it is bad for police, who would
benefit from clearer direction. Cf. Camreta v. Greene, 563
U. S. ___, ___–___ (2011) (slip op., at 10–11) (recognizing
the importance of clarifying the law).
   Of course, if the law enforcement system could not
function without permitting mistakes of law to justify
seizures, one could at least argue that permitting as much
is a necessary evil. But I have not seen any persuasive
argument that law enforcement will be unduly hampered
by a rule that precludes consideration of mistakes of law
in the reasonableness inquiry. After all, there is no indi-
cation that excluding an officer’s mistake of law from the
reasonableness inquiry has created a problem for law
enforcement in the overwhelming number of Circuits
which have adopted that approach. If an officer makes a
stop in good faith but it turns out that, as in this case, the
officer was wrong about what the law proscribed or re-
quired, I know of no penalty that the officer would suffer.
See 366 N. C. 271, 286–288, 

, 361–362
(2012) (Hudson, J., dissenting) (observing that “officers
(rightfully) face no punishment for a stop based on a mis-
take of law”). Moreover, such an officer would likely have
a defense to any civil suit on the basis of qualified immun-
——————
  1 Every other Circuit to have squarely addressed the question has

held that police mistakes of law are not a factor in the reasonableness
inquiry. See United States v. Miller, 

, 279 (CA5 1998);
United States v. McDonald, 

, 962 (CA7 2006); United
States v. King, 

, 741 (CA9 2001); United States v. Nichol-
son, 

, 1244 (CA10 2013); United States v. Chanthasouxat,

, 1279–1280 (CA11 2003). Five States have agreed. See
Hilton v. State, 

, 298 (Fla. 2007); State v. Louwrens, 

, 652 (Iowa 2010); Martin v. Kansas Dept. of Revenue, 

, 637–639, 

, 948 (2008); State v. Anderson, 

, 823–824 (Minn. 2004); State v. Lacasella, 

,
193–195, 

, 981–982 (2002).
6                   HEIEN v. NORTH CAROLINA

                       SOTOMAYOR, J., dissenting

ity. See Ashcroft v. al-Kidd, 563 U. S. ___, ___ (2011) (slip
op., at 12) (“Qualified immunity gives government officials
breathing room to make reasonable but mistaken judg-
ments about open legal questions”).
   Nor will it often be the case that any evidence that may
be seized during the stop will be suppressed, thanks to the
exception to the exclusionary rule for good-faith police
errors. See, e.g., Davis v. United States, 564 U. S. ___,
___–___ (2011) (slip op., at 8–9). It is true that, unlike
most States, North Carolina does not provide a good-faith
exception as a matter of state law, see State v. Carter, 322
N. C. 709, 721–724, 

, 560–562 (1988), but
North Carolina recognizes that it may solve any remedial
problems it may perceive on its own, see 

370
S. E. 2d, at 562; N. C. Gen. Stat. Ann. §15A–974 (2013)
(statutory good-faith exception).2 More fundamentally,
that is a remedial concern, and the protections offered by
the Fourth Amendment are not meant to yield to accom-
modate remedial concerns. Our jurisprudence draws a
sharp “analytica[l] distinct[ion]” between the existence of a
——————
    2 In
      addition to North Carolina, it appears that 13 States do not pro-
vide a good-faith exception. See State v. Marsala, 

, 151,

, 59 (1990); Dorsey v. State, 

, 814 (Del. 2000);
Gary v. State, 

, 574–575, 

, 428 (1992); State
v. Guzman, 

, 998, 

, 677 (1992); State v.
Cline, 

, 283 (Iowa 2000), abrogated on other grounds
by State v. Turner, 

(Iowa 2001); Commonwealth v.
Upton, 

, 370, n. 5, 

, 554, n. 5 (1985);
State v. Canelo, 139 N. H. 376, 383, 

, 1102 (1995); State
v. Johnson, 168 N. J. 608, 622–623, 

, 1281–1282 (2001);
State v. Gutierrez, 116 N. M. 431, 432, 

, 1053 (1993);
People v. Bigelow, 

417, 427, 

, 457–458
(1985); Commonwealth v. Edmunds, 

, 376, 

,
888 (1991); State v. Oakes, 

, 173, 

, 121 (1991);
State v. Afana, 

, 184, 

, 886 (2010);
see also People v. Krueger, 

, 61, 76, 

, 606,
612 (1996) (limiting the exception to situations where police have a
warrant).
                 Cite as: 574 U. S. ____ (2014)            7

                   SOTOMAYOR, J., dissenting

Fourth Amendment violation and the remedy for that
violation. Davis, 564 U. S., at ___ (slip op., at 14).
  In short, there is nothing in our case law requiring us to
hold that a reasonable mistake of law can justify a seizure
under the Fourth Amendment, and quite a bit suggesting
just the opposite. I also see nothing to be gained from
such a holding, and much to be lost.
                             III
  In reaching the contrary conclusion, the Court makes
both serious legal and practical errors. On the legal side,
the Court barely addresses Ornelas and the other cases
that frame the reasonableness inquiry around factual
determinations. Instead, in support of its conclusion that
reasonable suspicion “arises from the combination of an
officer’s understanding of the facts and his understanding
of the relevant law,” ante, at 6 (emphasis added), the
Court first reaches to founding-era customs statutes and
cases applying those statutes. It concedes, however, that
these cases are “not directly on point” because they say
nothing about the scope of the Fourth Amendment and are
instead equivalents of our modern-day qualified immunity
jurisprudence for civil damages. Ante, at 7.
   The only link in the tenuous chain the Court constructs
between those cases and this one that has anything to say
about the Fourth Amendment is Brinegar v. United States,

(1949). See ante, at 8. But all that our
opinion in Brinegar actually says is that probable cause
exists where “ ‘the facts and circumstances within [the
officers’] knowledge and of which they had reasonably
trustworthy information [are] sufficient in themselves to
warrant a man of reasonable caution in the belief that’ an
offense has been or is being 

–176 (quoting Carroll v. United States, 

,
162 (1925)). It thus states the uncontroversial proposition
that the probable-cause inquiry looks to the reasonable-
8                   HEIEN v. NORTH CAROLINA

                       SOTOMAYOR, J., dissenting

ness of an officer’s understanding of the facts. Indeed,
Brinegar is an odd case for the Court to rely on given that,
like the cases I discussed above, it subsequently empha-
sizes that “the mistakes must be those of reasonable men,
acting on facts leading sensibly to their conclusions of

(emphasis added). Again,
reasonable understandings of the facts, not reasonable
understandings of what the law says.3
    Further, the Court looks to our decision in Michigan v.
DeFillippo, 

(1979). This is a Fourth Amend-
ment case, but the Court’s reading of it imagines a holding
that is not rooted in the logic of the opinion. We held in
DeFillippo that an officer had probable cause to support
an arrest even though the ordinance that had allegedly
been violated was later held by the Michigan Court of
Appeals to be unconstitutional. This was so, we explained,
because the officer conducted an arrest after having ob-
served conduct that was criminalized by a presumptively
valid law at the time of that conduct. See 

(“At
th[e] time [of the arrest], of course, there was no control-
ling precedent that this ordinance was or was not consti-
tutional, and hence the conduct observed violated a pre-
sumptively valid ordinance”). We noted that it would have
been wrong for that officer not to enforce the law in that sit-
uation. See 

(“Police are charged to enforce laws
until and unless they are declared unconstitutional.
 . . . Society would be ill-served if its police officers took

——————
  3 The Court in fact errs even earlier in the chain when it represents

United States v. Riddle, 5 Cranch 311 (1809), as containing some broad
proposition. Ante, at 6–7. As Justice Story explained in a later case,
the tolerance of mistakes of law in cases like Riddle was a result of the
specific customs statute that Congress had enacted. The Apollon, 

, 373 (1824) (explaining that findings of probable cause
“ha[d] never been supposed to excuse any seizure, except where some
statute creates and defines the exemption from damages” (emphasis
added)).
                 Cite as: 574 U. S. ____ (2014)            9

                   SOTOMAYOR, J., dissenting

it upon themselves to determine which laws are and which
are not constitutionally entitled to enforcement”).
   DeFillippo thus did not involve any police “mistake” at
all. Rather, DeFillippo involved a police officer correctly
applying the law that was then in existence and that
carried with it a presumption of validity. Here, by con-
trast, police stopped Heien on suspicion of committing an
offense that never actually existed. Given that our hold-
ing in DeFillippo relied so squarely on the existence of a
law criminalizing the defendant’s conduct, and on the
presumption of validity that attends actual laws, it can
hardly be said to control where, as here, no law ever actu-
ally criminalized Heien’s conduct.
   On the practical side, the Court primarily contends that
an officer may confront “a situation in the field as to which
the application of a statute is unclear.” Ante, at 11. One
is left to wonder, however, why an innocent citizen should
be made to shoulder the burden of being seized whenever
the law may be susceptible to an interpretive question.
Moreover, the Court fails to reconcile its belief that the
Fourth Amendment gives officers leeway to address situa-
tions where the application of a criminal statute may be
unclear with our prior assumption that the Fourth
Amendment does not give officers such leeway where they
rely on a statute that authorizes police conduct that may
violate the Fourth Amendment. See Illinois v. Krull, 

, 355, n. 12, 359 (1987). Nor does it engage with
the analytic consequences of North Carolina’s similar
concession that it does not mean to claim “that an officer’s
mistaken understanding of the Fourth Amendment itself
can support a seizure if that understanding was reason-
able.” Brief for Respondent 29. It is not clear why an
officer’s mistaken understanding of other laws should be
viewed differently.
   While I appreciate that the Court has endeavored to set
some bounds on the types of mistakes of law that it thinks
10               HEIEN v. NORTH CAROLINA

                   SOTOMAYOR, J., dissenting

will qualify as reasonable, and while I think that the set of
reasonable mistakes of law ought to be narrowly circum-
scribed if they are to be countenanced at all, I am not at
all convinced that the Court has done so in a clear way. It
seems to me that the difference between qualified immun-
ity’s reasonableness standard—which the Court insists
without elaboration does not apply here—and the Court’s
conception of reasonableness in this context—which re-
mains undefined—will prove murky in application. See
ante, at 11. I fear the Court’s unwillingness to sketch a
fuller view of what makes a mistake of law reasonable
only presages the likely difficulty that courts will have
applying the Court’s decision in this case.
                       *      *     *
  To my mind, the more administrable approach—and the
one more consistent with our precedents and principles—
would be to hold that an officer’s mistake of law, no matter
how reasonable, cannot support the individualized suspi-
cion necessary to justify a seizure under the Fourth
Amendment. I respectfully dissent.