1
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.
2
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.
3
The origins of the presumption that witnesses will testify truthfully appear to extend back at least into the 19th century, see *154
ante, 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.