I join the Court's opinion; it demonstrates convincingly that the California statute at issue in this case, Cal. Penal Code Ann. 647(e) (West 1970), as interpreted by California courts, is unconstitutionally vague. Even if the defect identified by the Court were cured, however, I would hold that this statute violates the Fourth Amendment. 1 Merely to facilitate the general law enforcement objectives of investigating and preventing unspecified crimes, States may not authorize the arrest and criminal prosecution of an individual for failing to produce identification or further information on demand by a police officer.
[461 U. S. 352, 363] It has long been settled that the Fourth Amendment prohibits the seizure and detention or search of an individual's person unless there is probable cause to believe that he has committed a crime, except under certain conditions strictly defined by the legitimate requirements of law enforcement and by the limited extent of the resulting intrusion on individual liberty and privacy. See Davis v. Mississippi, 394 U. S. 721, 726 -727 (1969).
The scope of that exception to the probable-cause requirement for seizures of the person has been defined by a series of cases, beginning with Terry v. Ohio, 392 U.S. 1 (1968), holding that a police officer with reasonable suspicion of criminal activity, based on articulable facts, may detain a suspect briefly for purposes of limited questioning and, in so doing, may conduct a brief "frisk" of the suspect to protect himself from concealed weapons. See, e. g. , United States v. Brignoni-Ponce, 422 U. S. 873, 880 -884 (1975); Adams v. Williams, 407 U. S. 143, 145 -146 (1972). Where probable cause is lacking, we have expressly declined to allow significantly more intrusive detentions or searches on the Terry rationale, despite the assertion of compelling law enforcement interests.
"For all but those narrowly defined intrusions, the requisite `balancing' has been performed in centuries of precedent and is embodied in the principle that seizures are `reasonable' only if supported by probable cause. " Dunaway v. New York, 442 U. S. 200, 214 (1979). 2 [461 U. S. 352, 364] Terry and the cases following it give full recognition to law enforcement officers' need for an "intermediate" response, short of arrest, to suspicious circumstances; the power to effect a brief detention for the purpose of questioning is a powerful tool for the investigation and prevention of crimes.
Any person may, of course, direct a question to another person in passing. The Terry doctrine permits police officers to do far more: If they have the requisite reasonable suspicion, they may use a number of devices with substantial coercive impact on the person to whom they direct their attention, including an official "show of authority," the use of physical force to restrain him, and a search of the person for weapons.
Terry v. Ohio, supra, at 19, n. 16; see Florida v. Royer, 460 U. S. 491, 498 -499 (1983) (opinion of WHITE, J. ); United States v. Mendenhall, 446 U. S. 544, 554 (1980) (opinion of Stewart, J.). During such an encounter, few people will ever feel free not to cooperate fully with the police by answering their questions. Cf. 3 W. LaFave, Search and Seizure 9. 2, pp. 53-55 (1978). Our case reports are replete with examples of suspects' cooperation during Terry encounters, even when the suspects have a great deal to lose by co-operating. See, e. g. , Sibron v.
New York, 392 U. S. 40, 45 (1968); Florida v. Royer, supra, at 493-495. The price of that effectiveness, however, is intrusion on individual interests protected by the Fourth Amendment. We have held that the intrusiveness of even these brief stops for purposes of questioning is sufficient to render them "seizures" under the Fourth Amendment. See Terry v. Ohio, 392 U. S. , at 16 .
For precisely that reason, the scope of seizures of the person on less than probable cause that Terry [461 U. S. 352, 365] permits is strictly circumscribed to limit the degree of intrusion they cause. Terry encounters must be brief; the suspect must not be moved or asked to move more than a short distance; physical searches are permitted only to the extent necessary to protect the police officers involved during the encounter; and, most importantly, the suspect must be free to leave after a short time and to decline to answer the questions put to him. "[T]he person may be briefly detained against his will while pertinent questions are directed to him.
Of course, the person stopped is not obliged to answer, answers may not be compelled, and refusal to answer furnishes no basis for an arrest, although it may alert the officer to the need for continued observation. " Id. , at 34 (WHITE, J. , concurring). Failure to observe these limitations converts a Terry encounter into the sort of detention that can be justified only by probable cause to believe that a crime has been committed.
See Florida v. Royer, 460 U. S. , at 501 (opinion of WHITE, J. ); id. , at 509-511 (BRENNAN, J, concurring in result); Dunaway v. New York, supra, at 216. The power to arrest - or otherwise to prolong a seizure until a suspect had responded to the satisfaction of the police officers - would undoubtedly elicit cooperation from a high percentage of even those very few individuals not sufficiently coerced by a show of authority, brief physical detention, and a frisk. We have never claimed that expansion of the power of police officers to act on reasonable suspicion alone, or even less, would further no law enforcement interests.
See, e. g. , Brown v. Texas, 443 U. S. 47, 52 (1979). But the balance struck by the Fourth Amendment between the public interest in effective law enforcement and the equally public interest in safeguarding individual freedom and privacy from arbitrary governmental interference forbids such expansion. See Dunaway v. New York, supra; United States v. Brignoni-Ponce, 422 U. S. , at 878 . Detention beyond the limits [461 U. S.
352, 366] of Terry without probable cause would improve the effectiveness of legitimate police investigations by only a small margin, but it would expose individual members of the public to exponential increases in both the intrusiveness of the encounter and the risk that police officers would abuse their discretion for improper ends. Furthermore, regular expansion of Terry encounters into more intrusive detentions, without a clear connection to any specific underlying crimes, is likely to exacerbate ongoing tensions, where they exist, between the police and the public.
See Report of the National Advisory Commission on Civil Disorders 157-168 (1968). In sum, under the Fourth Amendment, police officers with reasonable suspicion that an individual has committed or is about to commit a crime may detain that individual, using some force if necessary, for the purpose of asking investigative questions. 3 They may ask their questions in a way calculated to obtain an answer. But they may not compel an answer, and they must allow the person to leave after a reasonably brief period of time unless the information they have acquired during the encounter has given them probable cause sufficient to justify an arrest.