with whom Justice Marshall joins, dissenting.
In an interview during his month-long hospitalization, in what was apparently a singular moment of lucid recollection, John Foster selected respondent James Owens’ photograph from an array of possible suspects and informed FBI Agent Thomas Mansfield that it was respondent who had attacked him with a metal pipe on the morning of April 12, 1982. Had Foster subsequently died from his injuries, there is no doubt that both the Sixth Amendment and the Federal Rules of Evidence would have barred Mansfield from repeating Foster’s out-of-court identification at trial. Fortunately, Foster survived the beating; his memory, however, did not, and by the time of respondent’s trial he could no longer recall his assailant or explain why he had previously identified respondent as such. This profound memory loss, therefore, rendered Foster no less a conduit for stale and inscrutable evidence than Mansfield would have been, yet the Court nevertheless concludes that because defense counsel was afforded an unrestricted opportunity to cross-examine him, *565Foster’s unadorned reiteration of his earlier statement did not deprive respondent of his constitutional right to confront the witness against him. In my view, the Court today reduces the right of confrontation to a purely procedural protection, and a markedly hollow one at that. Because I believe the Sixth Amendment guarantees criminal defendants the right to engage in cross-examination sufficient to “affor[d] the trier of fact a satisfactory basis for evaluating the truth of [a] prior statement,” California v. Green, 399 U. S. 149, 161 (1970), and because respondent clearly was not afforded such an opportunity here, I dissent.
HH
On April 12, 1982, Foster was brutally assaulted while on duty as a correctional counselor at the federal prison in Lompoc, California. His attacker beat him repeatedly about the head and upper body with a metal pipe, inflicting numerous and permanently disabling injuries, one of which was a profound loss of short-term memory. Foster spent nearly a month in the hospital recuperating from his injuries, much of that time in a state of semiconsciousness. Although numerous people visited him, including his wife who visited daily, Foster remembered none except Agent Mansfield. While he had no recollection of Mansfield’s first visit on April 19, he testified that his memory of the interview Mansfield conducted on May 5 was “vivid.” App. 28. In particular, he recalled telling Mansfield: “[A]fter I was hit I looked down and saw the blood on the floor, and jammed my finger into Owens’ chest, and said, ‘That’s enough of that,’ and hit my alarm button.” Id., at 31.
Foster testified that at the time he made these statements, he was certain that his memory was accurate. In addition, he recalled choosing respondent’s photograph from those Mansfield showed him. There is no dispute, however, that by the time of trial Foster could no longer remember who had assaulted him or even whether he had seen his attacker. *566Nor could he recall whether any of the prison officials or other persons who visited him in the hospital had ever suggested that respondent had beaten him. A medical expert who testified on behalf of the prosecution explained that Foster’s inability to remember most of the details of the assault was attributable to a gradual and selective memory loss caused by his head injuries.
t — H I — I
The principal witness against respondent was not the John Foster who took the stand in December 1983 — that witness could recall virtually nothing of the events of April 12, 1982, and candidly admitted that he had no idea whether respondent had assaulted him. Instead, respondent’s sole accuser was the John Foster who, on May 5,1982, identified respondent as his attacker. This John Foster, however, did not testify at respondent’s trial: the profound memory loss he suffered during the approximately 18 months following his identification prevented him from affirming, explaining, or elaborating upon his out-of-court statement just as surely and completely as his assertion of a testimonial privilege, or his death, would have. Thus, while the Court asserts that defense counsel had “realistic weapons” with which to impugn Foster’s prior statement, ante, at 560, it does not and cannot claim that cross-examination could have elicited any information that would have enabled a jury to evaluate the trustworthiness or reliability of the identification. Indeed, although the Court suggests that defense counsel was able to explore Foster’s “lack of care and attentiveness,” his “bad memory,” and the possibility that hospital visitors suggested respondent’s name to him, ante, at 559, 560, Foster’s memory loss precluded any such inquiries: he simply could not recall whether he had actually seen his assailant or even whether he had had an opportunity to see him, nor could he remember any of his visitors, let alone whether any of them had suggested that respondent had attacked him. Moreover, by the *567time of trial, Foster was unable to shed any light on the accuracy of his May 1982 recollection of the assault; the most he could state was that on the day of the interview he felt certain that his statements were true. As the court below found, “[cjlearly, two of the three dangers surrounding Foster’s out-of-court identifications — misperception and failure of memory — could not be mitigated in any way by the only cross-examination of Foster that was available to [respondent].” 789 F. 2d 750, 759 (CA9 1986).
In short, neither Foster nor the prosecution could demonstrate the basis for Foster’s prior identification. Nevertheless, the Court concludes that the Sixth Amendment presents no obstacle to the introduction of such an unsubstantiated out-of-court statement, at least not where the declarant testifies under oath at trial and is subjected to unrestricted cross-examination. According to the Court, the Confrontation Clause is simply a procedural trial right that “guarantees only an opportunity for effective cross-examination, not cross-examination that is effective in whatever way, and to whatever extent, the defense might wish.” Ante, at 559 (citations omitted; internal quotation marks omitted; emphasis in original).
Although the Court suggests that the result it reaches today follows naturally from our earlier cases, we have never before held that the Confrontation Clause protects nothing more than a defendant’s right to question live witnesses, no matter how futile that questioning might be. On the contrary, as the Court’s own recitation of our prior case law reveals, we have repeatedly affirmed that the right of confrontation ensures “an opportunity for effective cross-examination.” Delaware v. Fensterer, 474 U. S. 15, 20 (1985) (per curiam) (emphasis added); see also Nelson v. O’Neil, 402 U. S. 622, 629 (1971) (Confrontation Clause does not bar admission of out-of-court statement where defendant has “the benefit of full and effective cross-examination of [declarant]”) (emphasis added); California v. Green, 399 U. S., *568at 159 (introduction of out-of-court statement does not violate Confrontation Clause “as long as the defendant is assured of full and effective cross-examination at the time of trial”) (emphasis added). While we have rejected the notion that effectiveness should be measured in terms of a defendant’s ultimate success, we have never, until today, equated effectiveness with the mere opportunity to pose questions. Rather, consistent with the Confrontation Clause’s mission of “advancing] a practical concern for the accuracy of the truth-determining process in criminal trials,” Dutton v. Evans, 400 U. S. 74, 89 (1970), we have suggested that the touchstone of effectiveness is whether the cross-examination affords “ ‘the trier of fact... a satisfactory basis for evaluating the truth of the prior statement.’ ” Ibid, (quoting California v. Green, supra, at 161). See also Ohio v. Roberts, 448 U. S. 56, 73 (1980) (introduction of prior testimony where the declarant was unavailable at trial did not violate Confrontation Clause where previous cross-examination of declarant “afforded the trier of fact a satisfactory basis for evaluating the truth of the prior statement” (citation omitted; internal quotation marks omitted));1 Mancusi v. Stubbs, 408 U. S. 204, 216 (1972) *569(same). Where no opportunity for such cross-examination exists, we have recognized that the Sixth Amendment permits the introduction of out-of-court statements only when they bear sufficient independent “indicia of reliability. ” Dutton v. Evans, supra, at 89.
In dispensing with these substantive constitutional requirements today, the Court relies almost exclusively on our decision in Delaware v. Fensterer, supra, a case that did not involve the introduction of prior statements. Fensterer concerned an expert witness’ inability to remember which of three possible scientific theories he had used in formulating his opinion. Although Fensterer contended that the witness’ forgetfulness made it impossible to impeach the scientific validity of his conclusions, we noted that “an expert who cannot recall the basis for his opinion invites the jury to find that his opinion is as rehable as his memory.” Id., at 19. While the witness’ endorsement of a given scientific theory might have maximized the effectiveness of cross-examination, the Confrontation Clause guarantees only that level of effectiveness necessary to afford the factfinder a satisfactory basis for assessing the validity of the evidence offered. Thus, because the expert’s inability to remember the basis for his opinion was self-impeaching, the constitutional guarantee had clearly been satisfied.
Fensterer, therefore, worked no change in our Confrontation Clause jurisprudence, yet the Court purports to discern in it a principle under which all live testimony as to a witness’ past belief is constitutionally admissible, provided the de*570fendant is afforded an opportunity to question the witness. From this the Court derives the corollary that prior statements as to'past belief are equally admissible, again given the requisite opportunity for questioning the declarant at trial. Accordingly, the Court asserts, the Confrontation Clause draws no line “between a forgetful witness’ live testimony that he once believed this defendant to be the perpetrator of the crime, and the introduction of the witness’ earlier statement to that effect. ” Ante, at 560. The obvious shortcoming in this reasoning, of course, is that Fensterer announced no such blanket rule: while the expert’s memory lapse in that case was self-impeaching, it does not follow — and we have therefore never held — that all forgetfulness may be so characterized. Certainly in the present case, Foster’s inability in December 1983 to remember the events of April 1982 in no way impugned or otherwise cast doubt upon the accuracy or trustworthiness of his memory in May 1982, particularly in light of the uncontradicted medical testimony explaining that his forgetfulness was the result of the head injuries he sustained. Under our prior cases, then, the constitutional admissibility of Foster’s prior statement, and the testimony of the Court’s hypothetical witness who cannot recall the basis for his past belief, should depend on whether the memory loss so seriously impedes cross-examination that the fact-finder lacks an adequate basis upon which to assess the truth of the proffered evidence. Whatever may be said of the Court’s hypothetical, it is clear in the case before us that Foster’s near total loss of memory precluded any meaningful examination or assessment of his out-of-court statement and thus should have barred the admission of that statement.
To the extent the Court’s ruling is motivated by the fear that a contrary result will open the door to countless Confrontation Clause challenges to the admission of out-of-court statements, that fear is groundless. To begin with, cases such as the present one will be rare indeed. More typically, witnesses asserting a memory loss will either not suffer (or *571claim) a total inability to recollect, or will do so under circumstances that suggest bias or ulterior motive; in either case, given the threshold of “effectiveness” established by our prior decisions, the witness’ partial memory or self-interest in claiming a complete memory loss will afford the factfinder an adequate basis upon which to evaluate the reliability and trustworthiness of the out-of-court statement. Even in those relatively few cases where no such basis can be elicited, the prior statement is still admissible if it bears independent “indicia of reliability.” Finally, assessments of “effectiveness” for Confrontation Clause purposes are no different than those undertaken by courts in deciding common evidentiary questions, and thus should not prove unduly burdensome.2 In any event, to the extent such assessments prove inconvenient or troublesome, those burdens flow from our commitment to a Constitution that places a greater value on individual liberty than on efficient judicial administration.
1 — 1 HH 1 — 1
1 agree with the Court that the Confrontation Clause does not guarantee defendants the right to confront only those witnesses whose testimony is not marred by forgetfulness, *572confusion, or evasion, and that the right, of confrontation “‘is generally satisfied when the defense is given a full and fair opportunity to probe and expose these infirmities through cross-examination.’” Ante, at 558 (quoting Fensterer, 474 U. S., at 22). But as we stressed just last Term, this right to cross-examination “is essentially a ‘functional’ right designed to promote reliability in the truth-finding functions of a criminal trial.” Kentucky v. Stincer, 482 U. S. 730, 737 (1987). In the present case, respondent Owens was afforded no opportunity to probe and expose the infirmities of Foster’s May 5, 1982, recollections, for here cross-examination, the “greatest legal engine ever invented for the discovery of truth,” California v. Green, 399 U. S., at 158, stood as helpless as current medical technology before Foster’s profound memory loss. In concluding that respondent’s Sixth Amendment rights were satisfied by Foster’s mere presence in the courtroom, the Court reduces the right of confrontation to a hollow formalism. Because I believe the Confrontation Clause guarantees more than the right to ask questions of a live witness, no matter how dead that witness’ memory proves to be, I dissent.
In Ohio v. Roberts, the Court indicated that, for purposes of determining the constitutional admissibility of prior testimony where the declarant is unavailable at trial, it is unnecessary to consider whether defense counsel’s questioning at the prior hearing “surmount[ed] some inevitably nebulous threshold of ‘effectiveness,’ ” and held that “in all but. . . extraordinary cases, no inquiry into ‘effectiveness’ is required.” 448 U. S., at 73 n. 12. In so ruling, however, the Court did not dispense with the Sixth Amendment’s substantive minima of effectiveness, but rather rejected the claim that prior testimony should be deemed inherently unreliable where the declarant was cross-examined by an attorney whose performance is subsequently deemed ineffective in collateral habeas corpus proceedings. In this context, therefore, “effectiveness” obviously refers to the attorney’s performance, not the impediments to meaningful cross-examination created by a witness’ memory loss. Indeed, the footnote in question is appended to a sentence once again affirming the need for affording the factfinder an adequate basis for assessing the truth of prior statements, and the author of Roberts has twice since confirmed that the Sixth Amend*569ment guarantees an opportunity for meaningful cross-examination. See Kentucky v. Stincer, 482 U. S. 730, 739, n. 9 (1987) (Blackmun, J.) (a state rule precluding access to certain information before trial “may hinder [the] defendant’s opportunity for effective cross-examination at trial, and thus . . . may violate the Confrontation Clause”) (emphasis in original); Pennsylvania v. Ritchie, 480 U. S. 39, 63, n. 1 (1987) (Blackmun, J., concurring) (Fensterer “[did] not imply that concern about. . . effectiveness [of cross-examination] has no place in analysis under the Confrontation Clause”).
Indeed, in a case such as this one, the inquiry into the constitutional adequacy of defendant’s opportunity for cross-examination is identical to that required under Federal Rule of Evidence 804(a)(3), which deems a declarant “unavailable” if, at trial, he or she “testifies to a lack of memory of the subject matter of the declarant’s [prior] statement” (emphasis added). The Court today, of course, concludes that notwithstanding Rule 804(a)’s definition of unavailability, a prior identification is not hearsay under Rule 801(d)(1)(C), and is therefore admissible, as long as the declarant is subject to cross-examination concerning the statement itself, regardless of whether the declarant can recall the basis for that statement. See ante, at 561-564. Because I believe such a construction of Rule 801(d)(1)(C) renders it unconstitutional under the Confrontation Clause, I would require, consistent with Rule 804(a), that the declarant be subject to cross-examination as to the subject matter of the prior statement. See 4 J. Weinstein & M. Berger, Weinstein’s Evidence 801-120 to 801-121 (1987) (endorsing such a construction of Rule 801(d)(1)(C)).