opinion: Mr. Justice. Brennan
  delivéred the opinion of the Court.
  Appellant, the proprietor of a bookstore, was convicted in a California Municipal Court under a Los Angeles City ordinance which makes it unlawful “for any person to have in his possession any obscene or indecent writing, [or] book . . . [i]n any place of business where . . . books . . . are sold or kept for sale.” The offense was defined by the Municipal Court, and by the Appellate Department of the Superior Court, which affirmed, the Municipal Court judgment imposing a jail sentence on appellant, as consisting solely of the possession, in the appellant’s bookstore, of a certain book found upon judiciál investigation to be obscene. The. definition included no element of scienter — knowledge by appellant of the contents of the book — and thus the ordinance was construed as imposing a “strict” or “absolute” criminal liability. The appellant made timely objection bélow that if the' ordinance were so construed it would be in conflict with the Constitution of the United States. This contention, together with other contentions based on the Constitution, was rejected, and the case comes here on appeal. 28. U. S. C. § 1257 (2); 358 U. S. 926.
  Almost 30 years ago, Chief Justice Hughes declared for this Court: “It is no longer open to doubt that the liberty of the . press, and of speech, is within the liberty safeguarded by the due process clause of the Fourteenth Amendment from invasion by state action. It was found impossible to. conclude that this essential personal liberty of the citizen was left unprotected by the general guaranty of fundamental rights of person and property. Near v. Minnesota, 283 U. S. 697, 707. It is too familiar for citation that such has been the doctrine of this Court, in respect of these freedoms, ever since. And it also requires no elaboration that the free publication and dissemination of books and other forms of the printed word furnish very familiar applications of these constitutionally protected freedoms. It is of course no matter that the dissemination takes place under commercial auspices. See Joseph Burstyn, Inc., v. Wilson, 343 U. S. 495; Grosjean v. American Press Co., 297 U. S. 233. Certainly a retail bookseller plays a most significant role in the process of the distribution of books.
  California here imposed a strict or absolute criminal responsibility on appellant not to have obscene books in his shop. “The existence of a mens rea is the rule of, rather than the exception to, the principles of Anglo-American criminal jurisprudence.” Dennis v. United States, 341 U. S. 494, 500. Still, it is doubtless competent for the States to create, strict criminal liabilities by defining criminal offenses without any element of scienter— though even where no freedom-of-expression question is involved, there is precedent in this Court that this power is not without limitations. See Lambert v. California, 355 U. S. 225. But the'question here is as to the validity of this ordinance’s elimination of the scienter requirement — an elimination which may tend to work a substantial restriction on the freedom of speech and of the press. Our decisions furnish examples of legal devices and doctrines, in most applications consistent with the Constitution, which cannot be applied in settings where they have the collateral effect of inhibiting the freedom of expression, by making the individual the more reluctant to exercise it. The States generally may regulate the allocation of the burden of proof in their courts, and it is a common procedural device to impose on a taxpayer the burden of proving his entitlement to exemptions from taxation, but where we conceived that this device was being applied in a manner tending to cause even a self-imposed restriction of free expression, we struck down its application. Speiser v. Randall, 357 U. S. 513. See Near v. Minnesota, supra, at 712-713. It has been stated here that the usual doctrines as to the separability of constitutional and unconstitutional applications of statutes may not apply where their effect is to leave standing a statute patently capable of many unconstitutional applications, threatening those who validly exercise their rights of free expression with the expense and inconvenience of criminal prosecution. Thornhill v. Alabama, 310 U. S. 88, 97-98. Cf. Staub v. City of Baxley, 355 U. S. 313. And this Court has intimated that stricter standards of permissible statutory vagueness may be applied to a statute haying a potentially inhibiting effect on speech; a man may the less be required to act at his peril here, because the free dissemination of ideas may be the loser. Winters v. New York, 333 U. S. 507, 509-510, 517-518. Very much to the point here, where the question is the elimination of the mental element in an offense, is this Court’s holding in Wieman v. Updegraff, 344 U. S. 183. There an oath as to past freedom from membership in subversive^, organizations, exacted by a State as a qualification.for public employment, was held to violate the Constitution in that it made no distinction between members who had, and those who had not, known of the organization’s' character. The Court said of the elimination of scienter in this context: “To thus inhibit individual freedom of movement is to stifle the flow of democratic expression and controversy at,one of its chief sources.” Id., at 191.
  These principles guide us to our decision here. We have held that obscene speech and writings are not protected by the constitutional guarantees of freedom of speech and the press. Roth v. United States, 354 U. S. 476. The ordinance here in question, to. be sure, only imposes criminal sanctions on a bookseller if in fact there is to be found in his shop an obscene book. But our holding in Roth does not recognize any state power to restrict the dissemination of books which are not obscene; and we think this ordinance’s strict liability feature would tend seriously to have that effect, by penalizing booksellers, even though they had not the slightest notice of the character of the books they sold. The appellee and the court below analogize this strict liability penal ordinance to familiar forms of penal statutes which dispense with any element of knowledge on the part of the person charged, food and drug legislation being a principal example. We find the analogy instructive in our examination of the question before us. The usual rationale for such statutes is that the public interest in the purity of its food is so great as to warrant the imposition of the highest standard' of care on distributors — in fact .an absolute standard which will not hear the distributor’s plea as to the amount of care he has used. Cf. United States v. Balint, 258 U. S. 250, 252-253, 254. His ignorance of the character of the food is irrelevant. There is no specific constitutional inhibition against making the distributors of food the strictest censors of their merchandise, but- the constitutional guarantees of the freedom of speech and of the press stand in the way of imposing a similar requirement on the bookseller. By dispensing with any requirement of knowledge of the contents of the book on the part of the seller, the ordinance tends to. impose a severe limitation on the public’s access to constitutionally protected matter. For if the bookseller is criminally liable without knowledge of the contents, and the ordinance fulfills its purpose, he will tend to restrict the books he sells to those he has inspected; and thus the State will have imposed a restriction upon the distribution of constitutionally protected as well as obscene literature. It has been well observed of a statute construed as dispensing with any requirement of scienter that: “Every bookseller would be placed under an obligation to make himself aware of the contents of every book in his shop. ■ It would be altogether unreasonable to demand so near an approach to omniscience.” The King v. Ewart, 25 N. Z. L. R. 709, 729 (C. A.). And the bookseller’s burden would become the public’s burden, for by restricting him the public’s access to reading matter would be restricted. If the contents of bookshops and periodical stands were restricted to material of which their proprietors had made an inspection, they might be depleted indeed. The bookseller’s limitation in the amount of reading material with which he could familiarize himself, and his timidity in the face of. his absolute, criminal liability, thus would tend to restrict the public’s access to forms of the printed word which the .State could not constitutionally suppress directly. ' The bookseller’s self-censorship, compelled by the State, would be a censorship .affecting the whole public, hardly less virulent for being privately administered. Through it, the distribution of all books, both obscene and not obscene, would be impeded.
  It is argued that unless the scienter requirement is dispensed with, regulation of the distribution of obscene material will be ineffective, as booksellers will falsely disclaim knowledge of their books’ contents or falsely deny reason to suspect their obscenity. We might observe that it has been some time 'now since the law viewed itself as impotent to explore the actual 'state of a man’s mind. See Pound, The Role of the Will in Law, 68 Harv. L. Rev. 1. Cf. American Communications Assn. v. Douds, 339 U. S. 382, 411. Eyewitness testimony of a bookseller’s perusal of a book hardly need be á necessary element in proving his awareness of its contents. The circumstances may warrant-the inference that he was aware of what a book contained, despite his denial.
  We need not. and most definitely do not pass today on what sort of mental element is requisite to a constitutionally permissible prosecution of a bookseller for carrying an obscene book in stock; whether honest mistake as to whether its contents in fact constituted obscenity need be an excuse; whether there might be circumstances under which the State constitutionally might require that a bookseller investigate further, or might put on him the burden of explaining why he did not, and what such circumstances might be. Doubtless any form of criminal obscenity statute applicable to a bookseller will induce some tendency to self-censorship and have some inhibitory effect on the dissemination of material not obscene, but we consider today only one which goes to the extent of eliminating all mental elements from the crime.
  We have said: “The fundamental freedoms of speech and press have contributed greatly to the development and well-being of our free society and are indispensable to its continued growth. Ceaseless vigilance is the watchword to prevent their erosion by Congress or by the States. The door barring federal and state intrusion into this area 'cannot be left ajar; it must be kept tightly closed and opened only the slightest crack necessary to prevent encroachment upon more important interests.” Roth v. United States, supra, at 488. This ordinance opens that door too far. ■ The existence of the State’s power to prevent the distribution of obscene matter does not mean that there can be no constitutional barrier to any form of practical exercise of that power. Cf. Dean Milk Co. v. City of Madison, 340 U. S. 349. It is plain to us that the ordinance in question, though aimed at obscene matter, has such a tendency to inhibit constitutionally protected expression that it cannot stand under the Constitution.
  Reversed.
  The ordinance is § 41.01.1 of the Municipal Code of the City of Los Angeles. It provides:
  ■ “INDECENT WRITINGS, ETC. — POSSESSION PROHIBITED:
  “It shall be unlawful for any person to have in his possession any obscene ■ or indecent writing, book, pamphlet, picture, photograph, drawing, figure, motion picture film, phonograph recording, wire recording or transcription of any kind in any of the following places:
  “1. In any school, school-grounds, public park or playground or in any public place, grounds, street or way within 300 yards of any school, park or playground;
  “2. In any place of business where ice-cream, soft drinks, candy, food, school supplies, magazines, books, pamphlets, papers, pictures or postcards are sold or kept for sale;
  “3. In any toilet or restroom open to the public;
  “4. In any poolroom ór billiard parlor, or in any place where alcoholic liquor is sold or offered for sale to the public;
  ■’ “5. In any place where phonograph records, photographs, motion pictures, pr transcriptions of any kind are made, used, maintained, sold or exhibited.” .
  In this sort of proceeding, “the highest court of a State in which a decision could be had.” 28 U. S. C. § 1257. Cal. Const'., Art. VI, §§ 4, 4b, 5. See Edwards v. California, 314 U. S. 160, 171.
  See Hall, General Principles of Criminal Law, p. 280. The Appellate Department’s opinion is at 161 Cal. App. 2d Supp. 860, 327 P. 2d 636. The ordinance’s elimination of scienter was, in fact, a reason assigned by that court for upholding it as permissible supplementary municipal legislation against the contention that the field was occupied by' California Penal Code §311, a -state-wide obscenity statute which requires scienter..
  .These other contentions, which are made again here, aré that evidence of a nature constitutionally required to be allowed tc be given for- the defense as to the obscene character of a book was not permitted to be introduced; that a constitutionally impermissible standard of obscenity was applied by the trier of the facts; and that the book was not in fact obscene. In the light of our determination as to the constitutional permissibility of a strict liability law under the circumstances, presented by this ease, we need not pass on these questions: For the purposes of discussion, we shall assume without deciding that the book was correctly adjudged below to be obscene.
  See also Williams, Criminal Law — The General Part, p. 238 et seq.
  See Note, 61 Harv. L. Rev. 1208.
  In the Roth opinion there was also decided Alberts v. California, which dealt with the power of the States in this area.
  The effectiveness of absolute criminal liability laws in promoting caution has been subjected to criticism. See Hall, General Principles of Criminal Law, pp. 300-301. See generally Williams, Criminal Law—The General Part, pp. 267-274; Sayre, Public Welfare Offenses, 33 Col. L. Rev. 55; Mueller, On Common Law Mens Rea, 42 Minn. L. Rev. 1043; Morissette v. United States, 342 U. S. 246.
  Common-law prosecutions for the dissemination of obscene matter strictly adhered to the requirement of scienter. See the discussion in Attorney General v. Simpson, 93 Irish L. T. 33, 37-38 (Dist. Ct.). Cf. Obscene Publications Act, 1959, 7 & 8 Eliz. 2, c. 66, § 2 (5); American Law Institute Model Penal Code § 207.10 (7) (Tentative Draft No. 6, May 1957), and Comments, pp. 49-51.
  The general California obscenity statute, Penal Code § 311, requires scienter, see note 3, and was of course sustained b.y us in Roth v. United States, supra. See note 7.
  We emphasized in Roth, at p. 484, that there is a “limited area” where such other interests prevail, and we listed representative decisions in note 14 at that page.