with whom Mr. Justice Douglas and Mr. Justice Marshall join, dissenting.
Respondent was found guilty of armed robbery and assault, after the jury had been charged, in pertinent part, as follows:
“The law provides for certain disputable presumptions which are to be considered as evidence.
“A presumption is a deduction which the law expressly directs to be made from particular facts and is to be considered by you along with the other evidence. However, since these presumptions are disputable presumptions only, they may be out-weighed or equaled by other evidence. Unless out-weighed or equaled, however, they are to be accepted by you as true.
“The law presumes that the defendant is innocent, and this presumption follows the defendant until guilt is proved beyond a reasonable doubt.
“Every witness is presumed to speak the truth. This presumption may be overcome by the manner in which the witness testifies, by the nature of his or her testimony, by evidence affecting his or her character, interest, or motives, by contradictory evidence, or by a presumption.
“Burden of Proof. The burden is upon the State to prove the guilt of the defendant beyond a reasonable doubt.” (Emphasis added.)
A timely objection was taken to the part instructing upon the presumption of truthfulness. In my view *151the charge permitted the jury to convict even though the evidence may have failed to establish respondent’s guilt beyond a reasonable doubt, and therefore denied respondent due process of law.
The charge directed the jury to find that the State’s witnesses had spoken the truth, unless the presumption of truthfulness were “overcome” by demeanor, impeachment, or contradictory evidence. This instruction followed an earlier instruction that a presumption could be rebutted by other evidence which “out-weighed or equaled” the presumption, but that otherwise “the law expressly direct[ed]” that a finding be made in accordance with the presumption. Considered together, these instructions clearly required the jury to believe a witness’ testimony until his or her untruthfulness had been demonstrated by evidence making it appear as likely as not that the testimony was false.1 Since the State’s case rested almost entirely upon the testimony of two eyewitnesses and two police officers, see ante, at 142, and since respondent neither called witnesses nor took the stand himself, the practical effect of the court’s instructions was to convert the State’s burden of proving guilt beyond a reasonable doubt to proving guilt by a preponderance of the evidence.2
*152The reduction of the prosecution’s burden of persuasion to a preponderance clearly conflicts with the Due Process Clause guarantee that an accused shall not be convicted “except upon proof beyond a reasonable doubt of every fact necessary to constitute the crime with which he is charged.” In re Winship, 397 U. S. 358, 364 (1970). In Cool v. United States, 409 U. S. 100 (1972), we held that an “unacceptable risk” existed that the jury might have understood an instruction- — that certain defense testimony could properly be considered if found to be true beyond a reasonable doubt — as requiring that the defense testimony be considered only if believed beyond a reasonable doubt. Id., at 102 n. 3. Over a dissent which asserted that the Court was parsing instructions and engaging in semantical distinctions without considering the trial court’s charge to the jury as a whole, id., at 107-108, the instruction was found “fundamentally inconsistent” with our Winship decision, since a possibility existed that exculpatory testimony — that would have *153created a reasonable doubt in the minds of the jurors— had been rejected because not believable beyond a reasonable doubt. Id., at 104. Thus, the evil in Cool was the unacceptable risk that jurors would understand the instruction to require that defense testimony be rejected out of hand which, if considered, might have given rise to a reasonable doubt about the defendant’s guilt. Respondent suffered no less a constitutional deprivation when, in unequivocal terms, the jury was instructed to accept the statements of prosecution witnesses as true even though the jurors might have entertained substantial and reasonable doubts about the veracity of the testimony — but not sufficient to conclude that it was as likely as not that the testimony was false.
Moreover, the presumption-of-truthfulness instruction itself is constitutionally defective. In Turner v. United States, 396 U. S. 398 (1970), we approved an inference of “knowledge” from the fact of possessing smuggled heroin, because “'[cjommon sense’ . . . tells us that those who traffic in heroin will inevitably become aware that the product they deal in is smuggled,” id., at 417; at the same time, we rejected the presumption that possession of unstamped cocaine was prima facie evidence that the drug was not purchased in or from the original stamped container, because a “reasonable possibility” existed that the defendant “stole the cocaine himself or obtained it from a stamped package in possession of the actual thief.” Id., at 423-424 (emphasis added). In the instant case, common sense does not dictate that a prosecution witness who has sworn or affirmed to tell the truth will inevitably do so, and there is surely a reasonable possibility that he will fail to do so.3 Since here no defense witnesses were *154called, the practical effect of the presumption of truthfulness was to permit the jury to find each and every element of the crimes charged without requiring that the elements be proved beyond a reasonable doubt. The presumption itself thus violates the mandate of Winship that “every fact necessary to constitute the crime” be proved beyond a reasonable doubt. See Barnes v. United States, 412 U. S. 837, 854 (1973) (Brennan, J., dissenting).
Viewed in the context of the overall charge to the jury, the instructions were no less objectionable. To be sure— as had been the case in Cool — the jurors were instructed that guilt must be proved beyond a reasonable doubt. However, they were also directed in effect to ignore certain doubts they might have entertained concerning the credibility of the prosecution's witnesses. Had the instructions concerning the reasonable-doubt standard necessarily contradicted the instructions dealing with the burden of proof needed to overcome the truthfulness presumption, the constitutional objection might have been dissipated. But there is, in my view, an “unacceptable risk” that the jury understood the instructions unambiguously to require that they put to one side certain doubts about the credibility of the testimony they had heard and only then determine whether the evidence *155supported a finding of guilt beyond a reasonable doubt.4 I therefore conclude that the instructions are constitutionally infirm.
In this circumstance, the constitutional error inhering in the instruction cannot properly be viewed as harmless beyond a reasonable doubt. See Chapman v. California, 386 U. S. 18, 24 (1967). The reasonable-doubt standard reduces the risk that an error in factfinding could deprive an innocent man of his good name and freedom. See In re Winship, supra, at 363-364. It also impresses the jurors with their solemn responsibility to avoid being misled by suspicion, conjecture, or mere appearance, and to arrive at a state of certainty concerning the proper resolution of the relevant factual issues. Here, the truth-finding function of the jury was invaded and the State's burden of proving guilt beyond a reasonable doubt was diminished. When the reasonable-doubt standard has been thus compromised, it cannot be said beyond doubt that the error “made no contribution to a criminal conviction.” Harrington v. California, 395 U. S. 250, 255 (1969) (dissenting opinion). Rather, such an error so conflicts with an accused's right to a fair trial that the “infraction can never be treated as harmless error.” Chapman v. California, supra, at 23.
Due to the structuring of the instructions it is conceivable that the jurors would have understood that, since the presumption of innocence could be overcome only by proof of guilt beyond a reasonable doubt, the presumption of truthfulness could likewise be overcome only by evidence of untruthfulness beyond a reasonable doubt. If the instructions were in fact understood in this manner, the ensuing arguments concerning the unconstitutionality of the instructions would follow a fortiori.
The courts of appeals in every circuit have disapproved of presumption-of-truthfulness instructions and have often expressed their objections in terms of constitutional values. See McMillen v. United States, 386 F. 2d 29 (CA1 1967); United States v. Bilotti, 380 F. *1522d 649 (CA2 1967); United States v. Evans, 398 F. 2d 159 (CA3 1968); United States v. Safley, 408 F. 2d 603 (CA4 1969); United States v. Reid, 469 F. 2d 1094 (CA5 1972); United States v. Stroble, 431 F. 2d 1273 (CA6 1970); United States v. Dichiarinte, 385 F. 2d 333 (CA7 1967); United States v. Gray, 464 F. 2d 632 (CA8 1972); the instant case, Naughten v. Cupp, 476 F. 2d 845 (CA9 1972); United States v. Birmingham, 447 F. 2d 1313 (CA10 1971); Stone v. United States, 126 U. S. App. D. C. 369, 379 F. 2d 146 (1967). But the courts have been particularly concerned about the impact that such instructions might have when the defendant has not offered testimony. See United States v. Safley, supra, at 605; United States v. Boone, 401 F. 2d 659, 661 (CA3 1968); United States v. Evans, supra, at 162; United States v. Dichiarinte, supra, at 339; Stone v. United States, supra, at 370, 379 F. 2d, at 147; United States v. Johnson, 371 F. 2d 800, 805 (CA3 1967); United States v. Meisch, 370 F. 2d 768, 774 (CA3 1966). However, even in a situation where the defendant has introduced rebuttal testimony, the impact of the presumption on the parties will be imponderable and not necessarily equal. See McMillen v. United States, supra, at 33.
The origins of the presumption that witnesses will testify truthfully appear to extend back at least into the 19th century, see *154ante, at 144-145, when it was a widely held belief that a willful violation of the oath would expose the witness “at once to temporal and to eternal punishment.” T. Starkie, Law of Evidence 29 (10th Am. ed. 1876). In addition, at that time many of the common-law rules of incompetency were applied to disqualify individuals from testifying for reasons which today would merely be grounds for impeachment. See generally 9 W. Holdsworth, History of English Law 177-197 (1926); C. McCormick, Evidence, c. 7 (2d ed. 1972). Since that time, the rationale underlying the presumption has been substantially undercut.
The majority’s reliance on Boyd v. United States, 271 U. S. 104 (1926), ante, at 146-147, is misplaced. There it was found that an “ambiguous” statement in the charge in a criminal case was likely understood in its harmless sense because’ of additional curative instructions. Id., at 107. The disputed instruction, even if erroneous, concerned a question of law under the Harrison Anti-Narcotic Act not of constitutional dimension, and the Court relied on the fact that a proper objection had not been taken to the charge. See id., at 107-108.