with whom Justice Marshall and Justice Blackmun join, dissenting.
Criminal discovery is not a game. It is integral to the quest for truth and the fair adjudication of guilt or innocence. Violations of discovery rules thus cannot go uncorrected or undeterred without undermining the truthseeking process. The question in this case, however, is not whether discovery rules should be enforced but whether the need to correct and deter discovery violations requires a sanction that itself distorts the truthseeking process by excluding material evidence of innocence in a criminal case. I conclude that, at least where a criminal defendant is not personally responsible for the discovery violation, alternative sanctions are not only adequate to correct and deter discovery violations but are far superior to the arbitrary and disproportionate penalty imposed by the preclusion sanction. Because of this, and because the Court’s balancing test creates a conflict of interest in every case involving a discovery violation, I would hold that, absent evidence of the defendant’s personal involvement in a discovery violation, the Compulsory Process Clause per se bars discovery sanctions that exclude criminal defense evidence.
I
Before addressing the merits, I pause to explicate what I take as implicit in the Court’s conclusion that the defendant’s constitutional claims were “sufficiently well presented to the state courts to support our jurisdiction.” Ante, at 407, n. 9. I quite agree with the Court that the constitutional claims were not waived in the Appellate Court of Illinois, both because the defendant’s appellate brief adequately presented the Sixth Amendment claim, see ibid., and because the analysis in this case would essentially be the same under the Due Process Clause, see ante, at 406-407, n. 9. The Court does not, however, explain its conclusion that the constitutional claims were not waived at trial. I conclude that, although as a matter of Illinois law the defendant waived his federal con*420stitutional claims at trial, as a matter of federal law that waiver does not bar review in this Court.
The only legal challenge to the witness preclusion that the defendant raised at trial was one sentence in his motion for new trial stating: “The Court erred by not letting a witness for defendant testify before the Jury.” Record 412. The Appellate Court of Illinois stated that the only witness preclusion issue before it on appeal was whether “the trial court abused its discretion by excluding the testimony of a defense witness as a sanction for violation of the discovery rules.” 141 Ill. App. 3d 839, 841, 491 N. E. 2d 3, 4-5 (1986). The Appellate Court never addressed either the compulsory process or due process claims concerning witness preclusion, id., at 844-845, 491 N. E. 2d, at 6-7, even though the briefs implicitly presented the former claim and expressly asserted the latter. This alone may not warrant the assumption that the Appellate Court implicitly held that a motion for new trial stating that “the court erred” preserved only an abuse of discretion claim and waived any constitutional claims. But the Appellate Court of Illinois had already reached that holding in an identical case. See People v. Douthit, 51 Ill. App. 3d 751, 366 N. E. 2d 950 (1977). The court in Douthit stated:
“Despite appellate counsel’s excellent brief on the issue of the constitutionality, as applied to a criminal defendant of that portion of Supreme Court Rule 415(g)(i) (Ill. Rev. Stat. 1975, ch. 110A, par. 415(g)(i)) authorizing exclusion of evidence for failure to comply with a discovery rule, we deem that issue, raised for the first time on appeal, to have been waived. There is nothing in the record to indicate that defense counsel ever raised any constitutional objection during the extensive in-chambers discussion summarized above, nor did he do so in his post-trial motion, which requests a new trial solely on the ground that ‘[t]he court erred in ruling that the defendant could not call Glen Muench and Rocky Reed to testify to defendant’s state of intoxication at the time *421of the commission of the alleged burglary.’ As we read this motion, it raises only the non-constitutional question whether the trial court abused its discretion in exercising the exclusion sanction. Failure to raise an issue, including a constitutional issue, in the written motion for a new trial constitutes waiver of that issue and it cannot be urged as a ground for reversal on review.” Id., at 753-754, 366 N. E. 2d, at 952-953 (citations and footnotes omitted; emphasis added).
Although different districts of the Appellate Court of Illinois decided Douthit and this case, given that at trial both defendants presented identical challenges to the identical provision in the identical fashion, both appellate briefs raised the identical constitutional and nonconstitutional claims, and both districts considered only the abuse of discretion claim, I am constrained to conclude that in this case, like in Douthit, the Appellate Court of Illinois deemed the constitutional claims waived as a matter of Illinois law.
The conclusion that the Appellate Court of Illinois deemed the federal constitutional claims waived as a matter of state law does not, of course, mean that they are waived as a matter of federal law. “[W]e have consistently held that the question of when and how defaults in compliance with state procedural rules can preclude our consideration of a federal question is itself a federal question.” Henry v. Mississippi, 379 U. S. 443, 447 (1965). Specifically, it is well established that where a state court possesses the power to disregard a procedural default in exceptional cases, the state court’s failure to exercise that power in a particular case does not bar review in this Court. Williams v. Georgia, 349 U. S. 375, 383-384 (1955); see also Sullivan v. Little Hunting Park, Inc., 396 U. S. 229, 233-234 (1969); Henry, supra, at 449, n. 5. The Illinois Supreme and Appellate Courts possess such a power. Illinois Supreme Court Rule 615(a) provides: “Plain errors or defects affecting substantial rights may be noticed [on appeal] even though they were not brought to the *422attention of the trial court.” Those courts frequently rely on this provision to address, in their discretion, issues that have been waived at trial. See Jenner, Tone, & Martin, Historical and Practice Notes following Ill. Ann. Stat., ch. 110A, ¶615 (1985) (citing 16 appellate cases decided between 1979 and 1981 as examples of cases invoking plain error alone); see also, e. g., People v. Visnack, 135 Ill. App. 3d 113, 118, 481 N. E. 2d 744, 748 (1985) (invoking substantial rights exception despite waiver). Apparently, the Appellate Court below declined to exercise this discretion and deemed the waiver binding. Since, under Williams v. Georgia, such a decision does not bar our review, we are free to address the merits despite the state-law waiver.
II
A
On the merits, I start from the same premise as the Court— that the Compulsory Process Clause of the Sixth Amendment embodies a substantive right to present criminal defense evidence before a jury. See ante, at 408-409; see also, e. g., Pennsylvania v. Ritchie, 480 U. S. 39, 56 (1987). Although I thus join the Court in rejecting the State’s argument that the Clause embodies only the right to subpoena witnesses, I cannot agree with the Court’s assertion that “[t]he State’s argument is supported by the plain language of the Clause.” Ante, at 407. The Compulsory Process Clause provides that “[i]n all criminal prosecutions, the accused shall enjoy the right... to have compulsory process for obtaining witnesses in his favor.” This plain language supports the State’s argument only if one assumes that the most natural reading of constitutional language is the least meaningful. For the right to subpoena defense witnesses would be a hollow protection indeed if the government could simply refuse to allow subpoenaed defense witnesses to testify. As this Court has recognized for the last 20 years, the right to subpoena witnesses must mean the right to subpoena them for a useful *423purpose, and thus necessarily implies a substantive limitation on the government’s power to prevent those witnesses from testifying.
“The right to offer the testimony of witnesses, and to compel their attendance, if necessary, is in plain terms the right to present a defense, the right to present the defendant’s version of the facts as well as the prosecution’s to the jury so it may decide where the truth lies.” Washington v. Texas, 388 U. S. 14, 19 (1967) (emphasis added).
“The Framers of the Constitution did not intend to commit the futile act of giving to a defendant the right to secure the attendance of witnesses whose testimony he had no right to use.” Id., at 23.
The substantive limitation on excluding criminal defense evidence secured by the plain terms of the Compulsory Process Clause is also grounded in the general constitutional guarantee of due process. See Chambers v. Mississippi, 410 U. S. 284, 298-302 (1973); see also Rock v. Arkansas, 483 U. S. 44, 51 (1987); Crane v. Kentucky, 476 U. S. 683, 690-691 (1986).
The Compulsory Process and Due Process Clauses thus require courts to conduct a searching substantive inquiry whenever the government seeks to exclude criminal defense evidence. After all, “[f]ew rights are more fundamental than that of an accused to present witnesses in his own defense.” Chambers, supra, at 302. The exclusion of criminal defense evidence undermines the central truthseeking aim of our criminal justice system, see United States v. Nixon, 418 U. S. 683, 709 (1974), because it deliberately distorts the record at the risk of misleading the jury into convicting an innocent person. Surely the paramount value our criminal justice system places on acquitting the innocent, see, e. g., In re Winship, 397 U. S. 358 (1970), demands close scrutiny of any law preventing the jury from hearing evidence fa*424vorable to the defendant. On the other hand, the Compulsory Process Clause does not invalidate every restriction on the presentation of evidence. The Clause does not, for example, require criminal courts to admit evidence that is irrelevant, Crane, supra, at 689-690, testimony by persons who are mentally infirm, see Washington v. Texas, supra, at 23, n. 21, or evidence that represents a half-truth, see United States v. Nobles, 422 U. S. 225, 241 (1975). That the inquiry required under the Compulsory Process Clause is sometimes difficult does not, of course, justify abandoning the task altogether.
Accordingly, this Court has conducted searching substantive inquiries into the rationales underlying every challenged exclusion of criminal defense evidence that has come before it to date. That scrutiny has led the Court to strike as constitutionally unjustifiable “rules that prevent whole categories of defense witnesses from testifying on the basis of a priori categories that presume them unworthy of belief,” such as a rule against introducing the testimony of an alleged accomplice, Washington v. Texas, supra, at 22-23; an application of the hearsay rule to statements that “were originally made and subsequently offered at trial under circumstances that provided considerable assurance of their reliability,” Chambers, supra, at 300; the exclusion of evidence bearing on the credibility of a voluntary confession, Crane, supra, at 688-691; and a per se rule excluding all posthypnosis testimony, Rock, supra, at 56-62. Based on a thorough review of the relevant case law, this Court defined the standard governing the constitutional inquiry just last Term in Rock v. Arkansas, concluding that restrictions on the right to present criminal defense evidence can be constitutional only if they “ ‘accommodate other legitimate interests in the criminal trial process’ ” and are not “arbitrary or disproportionate to the purposes they are designed to serve.” Rock v. Arkansas, supra, at 55-56, quoting Chambers, supra, at 295.1
*425B
The question at the heart of this case, then, is whether precluding a criminal defense witness from testifying bears an arbitrary and disproportionate relation to the purposes of discovery, at least absent any evidence that the defendant was personally responsible for the discovery violations. This question is not answered by merely pointing out that discovery, like compulsory process, serves truthseeking interests. Compare ante, at 411-412. I would be the last to deny the utility of discovery in the truthseeking process. See Brennan, The Criminal Prosecution: Sporting Event or Quest for Truth?, 1963 Wash. U. L. Q. 279. By aiding effective trial preparation, discovery helps develop a full account of the relevant facts, helps detect and expose attempts to falsify evidence, and prevents factors such as surprise from influencing the outcome at the expense of the merits of the case. But these objectives are accomplished by compliance with the discovery rules, not by the exclusion of material evidence. Discovery sanctions serve the objectives of discovery by correcting for the adverse effects of discovery violations and deterring future discovery violations from occurring. If sanctions other than excluding evidence can sufficiently correct and deter discovery violations,2 then there is no reason to resort to a sanction that itself constitutes “a conscious mandatory distortion of the fact-finding process whenever applied.” Weinstein, Some Difficulties in Devising Rules for *426Determining Truth in Judicial Trials, 66 Colum. L. Rev. 223, 237 (1966).
(1)
The use of the preclusion sanction as a corrective measure — that is, as a measure for addressing the adverse impact a discovery violation might have on truthseeking in the case at hand — is asserted to have two justifications: (1) it bars the defendant from introducing testimony that has not been tested by discovery, see ante, at 411-413; and (2) it screens out witnesses who are inherently suspect because they were not disclosed until trial, see ante, at 413-416. The first justification has no bearing on this case because the defendant does not insist on a right to introduce a witness’ testimony without giving the prosecution an opportunity for discovery. He concedes that the trial court was within its authority in requiring the witness to testify first out of the presence of the jury, and he concedes that the trial court could have granted the prosecution a continuance to give it sufficient time to conduct further discovery concerning the witness and the proffered testimony. See Brief for Petitioner 18-19. He argues only that he should not be completely precluded from introducing the testimony.
Nobles and Brown v. United States, 356 U. S. 148, 156 (1958) are thus inapposite. Compare ante, at 412-413. In Nobles the defendant sought to impeach the credibility of prosecution witnesses with testimony from a defense investigator regarding statements those witnesses had made in interviews with the investigator. 422 U. S., at 227-229. The trial court ruled that the investigator could not testify unless the defense disclosed the report the investigator had written summarizing the interviews. Ibid. This Court properly rejected the defendant’s claim that his right to compulsory process had been violated because:
“The District Court did not bar the investigator’s testimony. Cf. Washington v. Texas, 388 U. S. 14, 19 (1967). *427It merely prevented respondent from presenting to the jury a partial view of the credibility issue by adducing the investigator’s testimony and thereafter refusing to disclose the contemporaneous report that might offer further critical insights. The Sixth Amendment does not confer the right to present testimony free from the legitimate demands of the adversarial system; one cannot invoke the Sixth Amendment as a justification for presenting what might have been a half-truth.” Id., at 241 (emphasis added).
Here, by contrast, the trial court did bar the proffered defense testimony. It did not, as in Nobles, simply condition the right to introduce the testimony on the defendant’s disclosure of evidence that might demonstrate weaknesses in the testimony. The authority of trial courts to prevent the presentation of a “half-truth” by ordering further discovery is thus not at issue here. For similar reasons, the holding in Brown (that a person who testifies at her own denaturalization proceeding waives her Fifth Amendment right not to answer questions on cross-examination) can have no bearing on this case.
Nor, despite the Court’s suggestions, see ante, at 414-417, is the preclusion at issue here justifiable on the theory that a trial court can exclude testimony that it presumes or finds suspect. In the first place, the trial court did not purport to rely on any such presumption or finding in this case. Rather, after ruling that he would exclude the testimony because of the discovery violation, the judge stated:
“Further, for whatever value it is, because this is a jury trial, I have a great deal of doubt in my mind as to the veracity of this young man that testified as to whether he was an eyewitness on the scene, sees guns that are wrapped up. He doesn’t know Ray but he stops Ray.
*428“At any rate, Mr. Wormley is not going to testify, be a witness in this courtroom.” App. 28 (emphasis added).
The judge gave no indication that he was willing to exclude the testimony based solely on its presumptive or apparent lack of credibility. Nor, apparently, would Illinois law allow him to do so. See generally, e. g., People v. Van Dyke, 414 Ill. 251, 254, 111 N. E. 2d 165, 167 (“The credibility of the witnesses presented, as well as the weight of the evidence, [is] for the jury to determine and the court will not substitute its judgment therefor”), cert. denied, 345 U. S. 978 (1953); Village of DesPlaines v. Winkelman, 270 Ill. 149, 159, 110 N. E. 417, 422 (1915) (“[I]t is . . . for the jury to determine ... to which witnesses they will give the greatest weight, and not for the court to tell them”). Indeed, far from being able to prevent the jury from hearing the testimony of witnesses that the trial court deems untrustworthy, Illinois trial courts are not even permitted to comment on the credibility of witnesses to the jury.3 No Illinois case interpreting Rule 415(g) suggests that the Rule gives a trial judge special authority to exclude criminal defense witnesses based on their apparent or presumed unreliability.
In addition, preventing a jury from hearing the proffered testimony based on its presumptive or apparent lack of credibility would be antithetical to the principles laid down in Washington v. Texas, 388 U. S., at 20-23, and reaffirmed in Rock v. Arkansas, 483 U. S., at 53-55. We there criticized rules that disqualified witnesses who had an interest in the *429litigation as having the “effect of suppressing the truth,” Washington v. Texas, supra, at 20, noting that:
“[Disqualifications for interest . . . rested on the unstated premises that the right to present witnesses was subordinate to the court’s interest in preventing perjury, and that erroneous decisions were best avoided by preventing the jury from hearing any testimony that might be perjured, even if it were the only testimony available on a crucial issue.
“ ‘. . . [T]he conviction of our time is that the truth is more likely to be arrived at by hearing the testimony of all persons of competent understanding who may seem to have knowledge of the facts involved in a case, leaving the credit and weight of such testimony to be determined by the jury or by the court.’ . . .
“. . . [W]e believe that [the latter] reasoning [is] required by the Sixth Amendment.” 388 U. S., at 21-22, quoting Rosen v. United States, 245 U. S. 467, 471 (1918).
See also Rock v. Arkansas, supra, at 53-55 (quoting and restating the above). The Court in Washington v. Texas accordingly concluded that “arbitrary rules that prevent whole categories of defense witnesses from testifying on the basis of a priori categories that presume them unworthy of belief” are unconstitutional. 388 U. S., at 22.
Although persons who are not identified as defense witnesses until trial may not be as trustworthy as other categories of persons, surely any presumption that they are so suspect that the jury can be prevented from even listening to their testimony is at least as arbitrary as presumptions excluding an accomplice’s testimony, Washington v. Texas, supra, hearsay statements bearing indicia of reliability, Chambers v. Mississippi, 410 U. S. 284 (1973), or a defendant’s posthypnosis testimony, Rock, supra—all of which have been declared unconstitutional. Compare ante, at 414-417. *430The proper method, under Illinois law4 and Washington v. Texas, supra, for addressing the concern about reliability is for the prosecutor to inform the jury about the circumstances casting doubt on the testimony, thus allowing the jury to determine the credit and weight it wants to attach to such testimony.5 The power of the court to take that kind of corrective measure is undisputed; the defendant concedes that the court could have allowed the prosecutor to comment on the defense’s failure to disclose the identity of the witness until trial. See Brief for Petitioner 18-19.
Leaving deterrence aside for the moment, then, precluding witness testimony is clearly arbitrary and disproportionate to the purpose discovery is intended to serve — advancing the quest for truth. Alternative sanctions — namely, granting the prosecution a continuance and allowing the prosecutor to comment on the witness concealment — can correct for any adverse impact the discovery violation would have on the truthseeking process. Moreover, the alternative sanctions, unlike the preclusion sanction, do not distort the truth-seeking process by excluding material evidence of innocence.
(2)
Of course, discovery sanctions must include more than corrective measures. They must also include punitive measures that can deter future discovery violations from taking place. Otherwise, parties will have little reason not to seek *431tactical advantages by purposefully violating discovery rules and orders. Those violations that are not caught and corrected will then impose a significant cost on the truthseeking process, see swpra, at 425; ante, at 411-412, that, in the long run, could conceivably outweigh the burden on truthseeking imposed by the preclusion sanction. Without some means of deterring discovery violations, moreover, the criminal system would continually be interrupted and distracted by continuances and other corrective measures. See ante, at 411.
In light of the availability of direct punitive measures, however, there is no good reason, at least absent evidence of the defendant’s complicity, to countenance the arbitrary and disproportionate punishment imposed by the preclusion sanction. The central point to keep in mind is that witness preclusion operates as an effective deterrent only to the extent that it has a possible effect on the outcome of the trial. Indeed, it employs in part the possibility that a distorted record •will cause a jury to convict a defendant of a crime he did not commit. • Witness preclusion thus punishes discovery violations in a way that is both disproportionate — it might result in a defendant charged with a capital offense being convicted and receiving a death sentence he would not have received but for the discovery violation — and arbitrary — it might, in another case involving an identical discovery violation, result in a defendant suffering no change in verdict or, if charged with a lesser offense, being convicted and receiving a light or suspended sentence. In contrast, direct punitive measures (such as contempt sanctions or, if the attorney is responsible, disciplinary proceedings) can gradate the punishment to correspond to the severity of the discovery violation.
The arbitrary and disproportionate nature of the preclusion sanction is highlighted where the penalty falls on the defendant even though he bore no responsibility for the discovery violation. In this case, although there was ample evidence that the defense attorney willfully violated Rule *432413(d),6 there was no evidence that the defendant played any role in that violation. Nor did the trial court make any effort to determine whether the defendant bore any responsibility for the discovery violation. Indeed, reading the record leaves the distinct impression that the main reason the trial court excluded Wormley’s testimony was the belief that the defense counsel had purposefully lied about when he had located Wormley. App. 25-28.
Worse yet, the trial court made clear that it was excluding Wormley’s testimony not only in response to the defense counsel’s actions in this case but also in response to the actions of other defense attorneys in other cases. The trial court stated:
“. . . All right, I am going to deny Wormley an opportunity to testify here. He is not going to testify. I find this a blatent [sic] violation of the discovery rules, willful violation of the rules. I also feel that defense attorneys have been violating discovery in this courtroom in the last three or four cases blatently [sic] and I am going to put a stop to it and this is one way to do so.” Id., at 28.
Although the Court recognizes this problem, it offers no response other than the cryptic statement that “[u]nrelated discovery violations . . . would not . . . normally provide a proper basis for curtailing the defendant’s constitutional right to present a complete defense.” Ante, at 416, n. 22. We are left to wonder either why this case is abnormal or why an exclusion founded on an improper basis should be upheld.
*433In the absence of any evidence that a defendant played any part in an attorney’s willful discovery violation, directly sanctioning the attorney is not only fairer but more effective in deterring violations than excluding defense evidence. Compare ante, at 413-414. The threat of disciplinary proceedings, fines, or imprisonment will likely influence attorney behavior to a far greater extent than the rather indirect penalty threatened by evidentiary exclusion. Such sanctions were available here. Rather than punishing the defendant under Rule 415(g)(i), the trial court could have sanctioned the attorney under Rule 415(g)(ii), which provides that “Wilful violation by counsel of an applicable discovery rule . . . may subject counsel to appropriate sanctions by the court.” See also App. 28 (threatening disciplinary proceedings). Direct sanctions against the attorney would have been particularly appropriate here since the discovery rule violated in this case places the obligation to comply with discovery not on the defendant, but directly on the attorney: providing that, upon motion by the State, a “defense counsel. . . shall furnish the State with . . . the names and last known addresses of persons he intends to call as witnesses . . . .” 111. Sup. Ct. Rule 413(d) (emphasis added).
The situation might be different if the defendant willfully caused the discovery violation because, as the Court points out, see ante, at 413-414, some defendants who face the prospect of a lengthy imprisonment are arguably impossible to deter with direct punitive sanctions such as contempt. But that is no explanation for allowing defense witness preclusion where there is no evidence that the defendant bore any responsibility for the discovery violation. At a minimum, we would be obligated to remand for further factfinding to establish the defendant’s responsibility. Deities may be able to visit the sins of the father on the son, but I cannot agree that courts should be permitted to visit the sins of the lawyer on the innocent client.
*434Nor is the issue resolved by analogizing to tactical errors an attorney might make such as failing to put witnesses on the stand that would have aided the defense. Compare ante, at 410, 417-418. Although we have sometimes held a defendant bound by tactical errors his attorney makes that fall short of ineffective assistance of counsel, we have not previously suggested that a client can be punished for an attorney’s misconduct. There are fundamental differences between attorney misconduct and tactical errors. Tactical errors are products of a legitimate choice among tactical options. Such tactical decisions must be made within the adversary system, and the system requires attorneys to make them, operating under the presumption that the attorney will choose the course most likely to benefit the defendant. Although some of these decisions may later appear erroneous, penalizing attorneys for such miscalculations is generally an exercise in futility because the error is usually visible only in hindsight — at the time the tactical decision was made there was no obvious “incorrect” choice, and no prohibited one. In other words, the adversary system often cannot effectively deter attorney’s tactical errors and does not want to deter tactical decisions. Thus, where a defense attorney makes a routine tactical decision not to introduce evidence at the proper time and the defense seeks to introduce the evidence later, deterrence measures may not be capable of preventing the untimely introduction of evidence from systemically disrupting trials, jury deliberations, or final verdicts. In those circumstances, treating the failure to introduce evidence at the proper time as a procedural default that binds the defendant is arguably the only means of systemically preventing such disruption — not because binding the defendant deters tactical errors any better than direct punitive sanctions but because binding the defendant to defense counsel’s procedural default, by definition, eliminates the disruption. The actual operation of the adversary system generally bears out the analysis outlined above. Direct punitive sanctions are *435not available to punish and deter routine tactical errors. If, however, the erroneous nature of the attorney’s decision was sufficiently evident at the time, then the system does want to deter the attorney’s behavior, and can and does do so by directly sanctioning the attorney for malpractice. It does not bind the defendant, who by establishing malpractice would have also established ineffective assistance of counsel.
The rationales for binding defendants to attorneys’ routine tactical errors do not apply to attorney misconduct. An attorney is never faced with a legitimate choice that includes misconduct as an option. Although it may be that “[t]he adversary process could not function effectively if every tactical decision required client approval,” ante, at 418, that concern is irrelevant here because a client has no authority to approve misconduct. Further, misconduct is not visible only with hindsight, as are many tactical errors. Consequently, misconduct is amenable to direct punitive sanctions against attorneys as a deterrent that can prevent attorneys from systemically engaging in misconduct that would disrupt the trial process. There is no need to take steps that will inflict the punishment on the defendant. Direct punitive sanctions are also more appropriate since the determination that misconduct occurred (and the level of penalty imposed) primarily turns on an assessment of the attorney’s culpability rather than, as with procedural defaults, an assessment of the potential for disrupting the trial system. In this case there is no doubt that willfully concealing the identity of witnesses one intends to call at trial is attorney misconduct, that the government seeks to deter such behavior in all instances, and that the attorney knows such behavior is misconduct and not a legitimate tactical decision at the time it occurs. Direct punitive sanctions against the attorney are available. See Rule 415(g)(ii). And the decision to impose the evidentiary exclusion penalty in this case clearly turned on an assessment of the attorney’s culpability. See App. 25-28; People v. Rayford, 43 Ill. App. 3d 283, 286, 356 N. E. 2d 1274, 1277 *436(1976) (exclusion only justifiable if the discovery violation is deliberate). No one contends that the same exclusion would have been justified if the failure to disclose Wormley’s identity had been inadvertent.7
C
In short, I can think of no scenario that does not involve a defendant’s willful violation of a discovery rule where alternative sanctions would not fully vindicate the purposes of discovery without distorting the truthseeking process by excluding evidence of innocence. Courts can couple corrective measures that will subject the testimony at issue to discovery and adverse credibility inferences with direct punitive measures that are both proportional to the discovery violation and directed at the actor responsible for it. Accordingly, absent evidence that the defendant was responsible for the discovery violation, the exclusion of criminal defense evidence is arbitrary and disproportionate to the purposes of discovery and criminal justice and should be per se unconstitutional. I thus cannot agree with the Court’s case-by-case balancing approach or with its conclusion in this case that the exclusion was constitutional.
The Court’s balancing approach, moreover, has the unfortunate effect of creating a conflict of interest in every case involving a willful discovery violation because the defense counsel is placed in a position where the best argument he can make on behalf of his client is: “Don’t preclude the defense witness — punish me personally. ” In this very case, for example, the defense attorney became noticeably timid once the judge threatened to report his actions to the disciplinary *437commission. App. 28-29. He did not argue: “Sure, bring me before the disciplinary commission; that’s a much more appropriate sanction than excluding a witness who might get my client acquitted.” I cannot see how we can expect defense counsel in this or any other case to act as vigorous advocates for the interests of their clients when those interests are adverse to their own.8
It seems particularly ironic that the Court should approve the exclusion of evidence in this case at a time when several of its Members have expressed serious misgivings about the evidentiary costs of exclusionary rules in other contexts. Surely the deterrence of constitutional violations cannot be less important than the deterrence of discovery violations. Nor can it be said that the evidentiary costs are more significant when they are imposed on the prosecution. For that would turn on its head what Justice Harlan termed the “fundamental value determination of our society that it is far worse to convict an innocent man than to let a guilty man go free.” In re Winship, 397 U. S., at 372 (concurring opinion).
Discovery rules are important, but only as a means for helping the criminal system convict the guilty and acquit the innocent. Precluding defense witness testimony as a sanction for a defense counsel’s willful discovery violation not only directly subverts criminal justice by basing convictions on a partial presentation of the facts, United States v. Nixon, 418 U. S., at 709, but is also arbitrary and disproportionate to any of the purposes served by discovery rules or discovery sanctions. The Court today thus sacrifices the paramount values of the criminal system in a misguided and unnecessary effort to preserve the sanctity of discovery. We may never *438know for certain whether the defendant or Bridges’ brother fired the shot for which the defendant was convicted. We do know, however, that the jury that convicted the defendant was not permitted to hear evidence that would have both placed a gun in Bridges’ brother’s hands and contradicted the testimony of Bridges and his brother that they possessed no weapons that evening — and that, because of the defense counsel’s 5-day delay in identifying a witness, an innocent man may be serving 10 years in prison. I dissent.
Although the Court in Rock was addressing the specific issue of the defendant’s right to offer his own testimony, it derived the standard it articu*425lated from general compulsory process case law on the theory that the right to present one’s own testimony extended at least as far as the right to present the testimony of others. 483 U. S., at 52-53.
Illinois Supreme Court Rule 415(g) alone supplies a broad array of available discovery sanctions:
“(i) If... a party has failed to comply with an applicable discovery rule ... the court may order such party to permit the discovery of material and information not previously disclosed, grant a continuance, exclude such evidence, or enter such other order as it deems just under the circumstances.
“(n) Wilful violation by counsel of an applicable discovery rule . . . may subject counsel to appropriate sanctions by the court.”
See, e. g., People v. Santucci, 24 Ill. 2d 93, 98, 180 N. E. 2d 491, 493 (1962) (“Ultimate decisions of fact must fairly be left to the jury, as must be the determination of the credibility of witnesses and the weight to be afforded their testimony, and to this end it is not the province of the judge, in a criminal case, to convey his opinions on such matters to the jurors by word or deed”); People v. Heidorn, 114 Ill. App. 3d 933, 936, 449 N. E. 2d 568, 572 (1983) (“While the trial judge has wide discretion in the conduct of trial, he must not make comments or insinuations, by word or conduct, indicative of an opinion on the credibility of a witness . . .”).
Cf. People v. Rayford, 43 Ill. App. 3d 283, 288, 356 N. E. 2d 1274, 1278 (1976). The reasons cited by Illinois courts for forbidding judicial comment do not apply with the same force to prosecutorial comment. See, e. g., Santucci, supra, at 98, 180 N. E. 2d, at 493; Heidorn, supra, at 937, 449 N. E. 2d, at 572.
Precluding a witness based solely on a judge’s belief that the witness lacks credibility might also implicate the constitutional right to a jury trial in that it usurps the jury’s central function of assessing the credibility of witnesses. The constitutional right to a jury trial would mean little if a judge could exclude any defense witness whose testimony he or she did not credit.
On the second day of trial, Tuesday, March 27, 1984, defense counsel moved to amend his “Answer to Discovery” to include Alfred Wormley as a defense witness, stating that the defendant had told him about Wormley earlier but that he had not been able to locate Wormley previously. App. 12-13. The next day Wormley testified that defense counsel had visited him at his home and served him with a subpoena on Wednesday, March 21, 1984, five days before the trial began. Id., at 22.
The witness preclusion sanction thus cannot be justified on the theory that the defendant waived his right to introduce Wormley by failing to name him prior to trial. Indeed, far from being a procedural default, the exclusion of evidence is an unusual sanction applied only in drastic cases, People v. Rayford, 43 Ill. App. 3d, at 286-287, 356 N. E. 2d, at 1277, and the decision whether to apply it lies in the discretion of the trial court, 141 Ill. App. 3d 839, 844-845, 491 N. E. 2d 3, 7 (1986) (case below).
I also note that a case-by-case balancing approach will create uncertainty, spawn unnecessary litigation, and make it difficult to supervise the lower courts. Moreover, any exclusion of criminal defense evidence also has the important disadvantage of inviting an ineffective-assistance-ofeounsel claim in every case in which it is applied. Direct sanctions against the attorney would yield no such opportunity to disrupt final verdicts.