JUSTICE O'CONNOR delivered the opinion of the Court, except as to Part IV-C.

In this case, we must decide whether petitioner, Johnny Paul Penry, was sentenced to death in violation of the Eighth Amendment because the jury was not instructed that it could consider and give effect to his mitigating evidence in imposing its sentence. We must also decide whether the Eighth Amendment categorically prohibits Penry's execution because he is mentally retarded.

I

On the morning of October 25, 1979, Pamela Carpenter was brutally raped, beaten, and stabbed with a pair of scissors in her home in Livingston, Texas. She died a few hours later in the course of emergency treatment. Before she died, she described her assailant. Her description led two local sheriff's deputies to suspect Penry, who had recently been released on parole after conviction on another rape charge. Penry subsequently gave two statements confessing to the crime and was charged with capital murder.

At a competency hearing held before trial, a clinical psychologist, Dr. Jerome Brown, testified that Penry was mentally retarded. As a child, Penry was diagnosed as having organic brain damage, which was probably caused by trauma to the brain at birth. App. 34-35. Penry was tested over the years as having an IQ between 50 and 63, which indicates mild to moderate retardation. Id., at 36-38, 55. Dr. Brown's own testing before the trial indicated that Penry had an IQ of 54. Dr. Brown's evaluation also revealed that Penry, who was 22 years old at the time of the crime, had the mental age of a 6 1/2-year-old, which means that "he has the ability to learn and the learning or the knowledge of the average 6 1/2 year old kid." Id., at 41. Penry's social maturity, or ability to function in the world, was that of a 9- or 10-year-old. Dr. Brown testified that "there's a point at which anyone with [Penry's] IQ is always incompetent, but, you know, this man is more in the borderline range." Id., at 47.

The jury found Penry competent to stand trial. Id., at 20-24. The guilt-innocence phase of the trial began on March 24, 1980. The trial court determined that Penry's confessions were voluntary, and they were introduced into evidence. At trial, Penry raised an insanity defense and presented the testimony of a psychiatrist, Dr. Jose Garcia. Dr. Garcia testified that Penry suffered from organic brain damage and moderate retardation, which resulted in poor impulse control and an inability to learn from experience. Id., at 18, 19, 87-90. Dr. Garcia indicated that Penry's brain damage was probably caused at birth, id., at 106, but may have been caused by beatings and multiple injuries to the brain at an early age. Id., at 18, 90. In Dr. Garcia's judgment, Penry was suffering from an organic brain disorder at the time of the offense which made it impossible for him to appreciate the wrongfulness of his conduct or to conform his conduct to the law. Id., at 86-87.

Penry's mother testified at trial that Penry was unable to learn in school and never finished the first grade. Penry's sister testified that their mother had frequently beaten him over the head with a belt when he was a child. Penry was also routinely locked in his room without access to a toilet for long periods of time. Id., at 124, 126, 127. As a youngster, Penry was in and out of a number of state schools and hospitals, until his father removed him from state schools altogether when he was 12. Id., at 120. Penry's aunt subsequently struggled for over a year to teach Penry how to print his name. Id., at 133.

The State introduced the testimony of two psychiatrists to rebut the testimony of Dr. Garcia. Dr. Kenneth Vogtsberger testified that although Penry was a person of limited mental ability, he was not suffering from any mental illness or defect at the time of the crime, and that he knew the difference between right and wrong and had the potential to honor the law. Id., at 144-145. In his view, Penry had characteristics consistent with an antisocial personality, including an inability to learn from experience and a tendency to be impulsive and to violate society's norms. Id., at 149-150. He testified further that Penry's low IQ scores under-estimated his alertness and understanding of what went on around him. Id., at 146.

Dr. Felix Peebles also testified for the State that Penry was legally sane at the time of the offense and had a "full-blown anti-social personality." Id., at 171. In addition, Dr. Peebles testified that he personally diagnosed Penry as being mentally retarded in 1973 and again in 1977, and that Penry "had a very bad life generally, bringing up." Id., at 168-169. In Dr. Peebles' view, Penry "had been socially and emotionally deprived and he had not learned to read and write adequately." Id., at 169. Although they disagreed with the defense psychiatrist over the extent and cause of Penry's mental limitations, both psychiatrists for the State acknowledged that Penry was a person of extremely limited mental ability, and that he seemed unable to learn from his mistakes. Id., at 149, 172-173.

The jury rejected Penry's insanity defense and found him guilty of capital murder. Tex. Penal Code Ann. § 19.03 (1974 and Supp. 1989). The following day, at the close of the penalty hearing, the jury decided the sentence to be imposed on Penry by answering three "special issues":

"(1) whether the conduct of the defendant that caused the death of the deceased was committed deliberately and with the reasonable expectation that the death of the deceased or another would result;

"(2) whether there is a probability that the defendant would commit criminal acts of violence that would constitute a continuing threat to society; and

"(3) if raised by the evidence, whether the conduct of the defendant in killing the deceased was unreasonable in response to the provocation, if any, by the deceased." Tex. Code Crim. Proc. Ann., Art. 37.071(b) (Vernon 1981 and Supp. 1989).

If the jury unanimously answers "yes" to each issue submitted, the trial court must sentence the defendant to death. Arts. 37.071(c)-(e). Otherwise, the defendant is sentenced to life imprisonment. Ibid.

Defense counsel raised a number of objections to the proposed charge to the jury. With respect to the first special issue, he objected that the charge failed to define the term "deliberately." App. 210. With respect to the second special issue, he objected that the charge failed to define the terms "probability," "criminal acts of violence," and "continuing threat to society." Id., at 210-211. Defense counsel also objected to the charge because it failed to "authorize a discretionary grant of mercy based upon the existence of mitigating circumstances" and because it "fail[ed] to require as a condition to the assessment of the death penalty that the State show beyond a reasonable doubt that any aggravating circumstances found to exist outweigh any mitigating circumstances." Id., at 211. In addition, the charge failed to instruct the jury that it may take into consideration all of the evidence whether aggravating or mitigating in nature which was submitted in the full trial of the case. Id., at 212. Defense counsel also objected that, in light of Penry's mental retardation, permitting the jury to assess the death penalty in this case amounted to cruel and unusual punishment prohibited by the Eighth Amendment. Id., at 211.

These objections were overruled by the trial court. The jury was then instructed that the State bore the burden of proof on the special issues, and that before any issue could be answered "yes," all 12 jurors must be convinced by the evidence beyond a reasonable doubt that the answer to that issue should be "yes." Id., at 25. The jurors were further instructed that in answering the three special issues, they could consider all the evidence submitted in both the guilt-innocence phase and the penalty phase of the trial. Id., at 26. The jury charge then listed the three questions, with the names of the defendant and the deceased inserted.

The jury answered "yes" to all three special issues, and Penry was sentenced to death. The Texas Court of Criminal Appeals affirmed his conviction and sentence on direct appeal. Penry v. State, 691 S.W.2d 636 (1985). That court held that terms such as "deliberately," "probability," and "continuing threat to society" used in the special issues need not be defined in the jury charge because the jury would know their common meaning. Id., at 653-654. The court concluded that Penry was allowed to present all relevant mitigating evidence at the punishment hearing, and that there was no constitutional infirmity in failing to require the jury to find that aggravating circumstances outweighed mitigating ones or in failing to authorize a discretionary grant of mercy based upon the existence of mitigating circumstances. Id., at 654. The court also held that imposition of the death penalty was not prohibited by virtue of Penry's mental retardation. Id., at 654-655. This Court denied certiorari on direct review. Sub nom. Penry v. Texas, 474 U.S. 1073 (1986).

Penry then filed this federal habeas corpus petition challenging his death sentence. Among other claims, Penry argued that he was sentenced in violation of the Eighth Amendment because the trial court failed to instruct the jury on how to weigh mitigating factors in answering the special issues and failed to define the term "deliberately." Penry also argued that it was cruel and unusual punishment to execute a mentally retarded person. The District Court denied relief, App. 234-273, and Penry appealed to the Court of Appeals for the Fifth Circuit.

The Court of Appeals affirmed the District Court's judgment. 832 F.2d 915 (1987). The court stressed, however, that it found considerable merit in Penry's claim that the jury was not allowed to consider and apply all of his personal mitigating circumstances in answering the Texas special issues. Although the jury was presented with evidence that might mitigate Penry's personal culpability for the crime, such as his mental retardation, arrested emotional development, and abused background, the jury could not give effect to that evidence by mitigating Penry's sentence to life imprisonment. "Having said that it was a deliberate murder and that Penry will be a continuing threat, the jury can say no more." Id., at 920. In short, the court did not see how Penry's mitigating evidence, under the instructions given, could be fully acted upon by the jury because "[t]here is no place for the jury to say 'no' to the death penalty" based on the mitigating force of those circumstances. Id., at 925. Although the court questioned whether Penry was given the individualized sentencing that the Constitution requires, it ultimately concluded that prior Circuit decisions required it to reject Penry's claims. Id., at 926. The court also rejected Penry's contention that it was cruel and unusual punishment to execute a mentally retarded person such as himself. Id., at 918 (citing Brogdon v. Butler, 824 F.2d 338, 341 (CA5 1987)).

We granted certiorari to resolve two questions. 487 U.S. 1233 (1988). First, was Penry sentenced to death in violation of the Eighth Amendment because the jury was not adequately instructed to take into consideration all of his mitigating evidence and because the terms in the Texas special issues were not defined in such a way that the jury could consider and give effect to his mitigating evidence in answering them? Second, is it cruel and unusual punishment under the Eighth Amendment to execute a mentally retarded person with Penry's reasoning ability?

II A

Penry is currently before the Court on his petition in federal court for a writ of habeas corpus. Because Penry is before us on collateral review, we must determine, as a threshold matter, whether granting him the relief he seeks would create a "new rule." Teague v. Lane, 489 U.S. 288, 301 (1989). Under Teague, new rules will not be applied or announced in cases on collateral review unless they fall into one of two exceptions. Id., at 311-313.

Teague was not a capital case, and the plurality opinion expressed no views regarding how the retroactivity approach adopted in Teague would be applied in the capital sentencing context. Id., at 314, n. 2. The plurality noted, however, that a criminal judgment necessarily includes the sentence imposed, and that collateral challenges to sentences "delay the enforcement of the judgment at issue and decrease the possibility that 'there will at some point be the certainty that comes with an end to litigation.'" Ibid. (quoting Sanders v. United States, 373 U.S. 1, 25 (1963) (Harlan, J., dissenting)). See also Mackey v. United States, 401 U.S. 667, 690-695 (1971) (Harlan, J., concurring in judgments in part and dissenting in part). In our view, the finality concerns underlying Justice Harlan's approach to retroactivity are applicable in the capital sentencing context, as are the two exceptions to his general rule of nonretroactivity. See Teague, supra, at 311-313.

B

As we indicated in Teague, "[i]n general . . . a case announces a new rule when it breaks new ground or imposes a new obligation on the States or the Federal Government." 489 U.S., at 301. Or, "[t]o put it differently, a case announces a new rule if the result was not dictated by precedent existing at the time the defendant's conviction became final." Ibid. (emphasis in original). Teague noted that "[i]t is admittedly often difficult to determine when a case announces a new rule." Ibid. Justice Harlan recognized "the inevitable difficulties that will arise in attempting 'to determine whether a particular decision has really announced a "new" rule at all or whether it has simply applied a well-established constitutional principle to govern a case which is closely analogous to those which have been previously considered in the prior case law.'" Mackey, supra, at 695 (opinion concurring in judgments in part and dissenting in part) (quoting Desist v. United States, 394 U.S. 244, 263 (1969) (Harlan, J., dissenting)). See generally Yates v. Aiken, 484 U.S. 211, 216-217 (1988) (concluding that Francis v. Franklin, 471 U.S. 307 (1985), did not announce a new rule but was "merely an application of the principle that governed our decision in Sandstrom v. Montana, [ 442 U.S. 510 (1979),] which had been decided before petitioner's trial took place").

Penry's conviction became final on January 13, 1986, when this Court denied his petition for certiorari on direct review of his conviction and sentence. Sub nom. Penry v. Texas, supra. This Court's decisions in Lockett v. Ohio, 438 U.S. 586 (1978), and Eddings v. Oklahoma, 455 U.S. 104 (1982), were rendered before his conviction became final. Under the retroactivity principles adopted in Griffith v. Kentucky, 479 U.S. 314 (1987), Penry is entitled to the benefit of those decisions. Citing Lockett and Eddings, Penry argues that he was sentenced to death in violation of the Eighth Amendment because, in light of the jury instructions given, the jury was unable to fully consider and give effect to the mitigating evidence of his mental retardation and abused background, which he offered as the basis for a sentence less than death. Penry thus seeks a rule that when such mitigating evidence is presented, Texas juries must, upon request, be given jury instructions that make it possible for them to give effect to that mitigating evidence in determining whether a defendant should be sentenced to death. We conclude, for the reasons discussed below, that the rule Penry seeks is not a "new rule" under Teague.

Penry does not challenge the facial validity of the Texas death penalty statute, which was upheld against an Eighth Amendment challenge in Jurek v. Texas, 428 U.S. 262 (1976). Nor does he dispute that some types of mitigating evidence can be fully considered by the sentencer in the absence of special jury instructions. See Franklin v. Lynaugh, 487 U.S. 164, 175 (1988) (plurality opinion); id., at 185-186 (O'CONNOR, J., concurring in judgment). Instead, Penry argues that, on the facts of this case, the jury was unable to fully consider and give effect to the mitigating evidence of his mental retardation and abused background in answering the three special issues. In our view, the relief Penry seeks does not "impos[e] a new obligation" on the State of Texas. Teague, supra, at 301. Rather, Penry simply asks the State to fulfill the assurance upon which Jurek was based: namely, that the special issues would be interpreted broadly enough to permit the sentencer to consider all of the relevant mitigating evidence a defendant might present in imposing sentence.

In Jurek, the joint opinion of Justices Stewart, Powell, and STEVENS noted that the Texas statute narrowed the circumstances in which the death penalty could be imposed to five categories of murders. 428 U.S., at 268. Thus, although Texas had not adopted a list of statutory aggravating factors that the jury must find before imposing the death penalty, "its action in narrowing the categories of murders for which a death sentence may ever be imposed serves much the same purpose," id., at 270, and effectively "requires the sentencing authority to focus on the particularized nature of the crime." Id., at 271. To provide the individualized sentencing determination required by the Eighth Amendment, however, the sentencer must be allowed to consider mitigating evidence. Ibid. Indeed, as Woodson v. North Carolina, 428 U.S. 280 (1976), made clear, "in capital cases the fundamental respect for humanity underlying the Eighth Amendment . . . requires consideration of the character and record of the individual offender and the circumstances of the particular offense as a constitutionally indispensable part of the process of inflicting the penalty of death." Id., at 304 (plurality opinion).

Because the Texas death penalty statute does not explicitly mention mitigating circumstances, but rather directs the jury to answer three questions, Jurek reasoned that the statute's constitutionality "turns on whether the enumerated questions allow consideration of particularized mitigating factors." 428 U.S., at 272. Although the various terms in the special questions had yet to be defined, the joint opinion concluded that the sentencing scheme satisfied the Eighth Amendment on the assurance that the Texas Court of Criminal Appeals would interpret the question concerning future dangerousness so as to allow the jury to consider whatever mitigating circumstances a defendant may be able to show, including a defendant's prior criminal record, age, and mental or emotional state. Id., at 272-273.

Our decisions subsequent to Jurek have reaffirmed that the Eighth Amendment mandates an individualized assessment of the appropriateness of the death penalty. In Lockett v. Ohio, 438 U.S. 586 (1978), a plurality of this Court held that the Eighth and Fourteenth Amendments require that the sentencer "not be precluded from considering, as a mitigating factor, any aspect of a defendant's character or record and any of the circumstances of the offense that the defendant proffers as a basis for a sentence less than death." Id., at 604 (emphasis in original). Thus, the Court held unconstitutional the Ohio death penalty statute which mandated capital punishment upon a finding of one aggravating circumstance unless one of three statutory mitigating factors were present.

Lockett underscored Jurek's recognition that the constitutionality of the Texas scheme "turns on whether the enumerated questions allow consideration of particularized mitigating factors." Jurek, supra, at 272. The plurality opinion in Lockett indicated that the Texas death penalty statute had "survived the petitioner's Eighth and Fourteenth Amendment attack [in Jurek] because three Justices concluded that the Texas Court of Criminal Appeals had broadly interpreted the second question — despite its facial narrowness — so as to permit the sentencer to consider 'whatever mitigating circumstances' the defendant might be able to show." 438 U.S., at 607. Thus, the Lockett plurality noted that neither the Texas statute upheld in 1976 nor the statutes that had survived facial challenges in Gregg v. Georgia, 428 U.S. 153 (1976), and Proffitt v. Florida, 428 U.S. 242 (1976), "clearly operated at that time to prevent the sentencer from considering any aspect of the defendant's character and record or any circumstances of his offense as an independently mitigating factor." Lockett, supra, at 607. Cf. Hitchcock v. Dugger, 481 U.S. 393 (1987) (sustaining "as applied" challenge to Florida death penalty statute); Godfrey v. Georgia, 446 U.S. 420 (1980) (sustaining "as applied" challenge to Georgia death penalty statute).

In Eddings v. Oklahoma, 455 U.S. 104 (1982), a majority of the Court reaffirmed that a sentencer may not be precluded from considering, and may not refuse to consider, any relevant mitigating evidence offered by the defendant as the basis for a sentence less than death. In Eddings, the Oklahoma death penalty statute permitted the defendant to introduce evidence of any mitigating circumstance, but the sentencing judge concluded, as a matter of law, that he was unable to consider mitigating evidence of the youthful defendant's troubled family history, beatings by a harsh father, and emotional disturbance. Applying Lockett, we held that "[j]ust as the State may not by statute preclude the sentencer from considering any mitigating factor, neither may the sentencer refuse to consider, as a matter of law, any relevant mitigating evidence." 455 U.S., at 113-114 (emphasis in original). In that case, "it was as if the trial judge had instructed a jury to disregard the mitigating evidence [the defendant] proffered on his behalf." Id., at 114.

Thus, at the time Penry's conviction became final, it was clear from Lockett and Eddings that a State could not, consistent with the Eighth and Fourteenth Amendments, prevent the sentencer from considering and giving effect to evidence relevant to the defendant's background or character or to the circumstances of the offense that mitigate against imposing the death penalty. Moreover, the facial validity of the Texas death penalty statute had been upheld in Jurek on the basis of assurances that the special issues would be interpreted broadly enough to enable sentencing juries to consider all of the relevant mitigating evidence a defendant might present. Penry argues that those assurances were not fulfilled in his particular case because, without appropriate instructions, the jury could not fully consider and give effect to the mitigating evidence of his mental retardation and abused childhood in rendering its sentencing decision. The rule Penry seeks — that when such mitigating evidence is presented, Texas juries must, upon request, be given jury instructions that make it possible for them to give effect to that mitigating evidence in determining whether the death penalty should be imposed — is not a "new rule" under Teague because it is dictated by Eddings and Lockett. Moreover, in light of the assurances upon which Jurek was based, we conclude that the relief Penry seeks does not "impos[e] a new obligation" on the State of Texas. Teague, 489 U.S., at 301.

III

Underlying Lockett and Eddings is the principle that punishment should be directly related to the personal culpability of the criminal defendant. If the sentencer is to make an individualized assessment of the appropriateness of the death penalty, "evidence about the defendant's background and character is relevant because of the belief, long held by this society, that defendants who commit criminal acts that are attributable to a disadvantaged background, or to emotional and mental problems, may be less culpable than defendants who have no such excuse." California v. Brown, 479 U.S. 538, 545 (1987) (O'CONNOR, J., concurring). Moreover, Eddings makes clear that it is not enough simply to allow the defendant to present mitigating evidence to the sentencer. The sentencer must also be able to consider and give effect to that evidence in imposing sentence. Hitchcock v. Dugger, supra. Only then can we be sure that the sentencer has treated the defendant as a "uniquely individual human bein[g]" and has made a reliable determination that death is the appropriate sentence. Woodson, 428 U.S., at 304, 305. "Thus, the sentence imposed at the penalty stage should reflect a reasoned moral response to the defendant's background, character, and crime." California v. Brown, supra, at 545 (O'CONNOR, J., concurring) (emphasis in original).

Although Penry offered mitigating evidence of his mental retardation and abused childhood as the basis for a sentence of life imprisonment rather than death, the jury that sentenced him was only able to express its views on the appropriate sentence by answering three questions: Did Penry act deliberately when he murdered Pamela Carpenter? Is there a probability that he will be dangerous in the future? Did he act unreasonably in response to provocation? The jury was never instructed that it could consider the evidence offered by Penry as mitigating evidence and that it could give mitigating effect to that evidence in imposing sentence.

Like the petitioner in Franklin v. Lynaugh, Penry contends that in the absence of his requested jury instructions, the Texas death penalty statute was applied in an unconstitutional manner by precluding the jury from acting upon the particular mitigating evidence he introduced. Franklin was the first case considered by this Court since Jurek to address a claim concerning the treatment of mitigating evidence under the Texas special issues. Like Jurek itself, Franklin did not produce a majority opinion for the Court. The Franklin plurality, and the two concurring Justices, concluded that Franklin was not sentenced to death in violation of the Eighth Amendment because the jury was free to give effect to his mitigating evidence of good behavior in prison by answering "no" to the question on future dangerousness. 487 U.S., at 177 (plurality opinion); id., at 185 (O'CONNOR, J., concurring in judgment). Moreover, a majority agreed that "residual doub[t]" as to Franklin's guilt was not a constitutionally mandated mitigating factor. Id., at 173, and n. 6 (plurality opinion); id., at 187-188 (O'CONNOR, J., concurring in judgment).

In Franklin, however, the five concurring and dissenting Justices did not share the plurality's categorical reading of Jurek. In the plurality's view, Jurek had expressly and unconditionally upheld the manner in which mitigating evidence is considered under the special issues. Id., at 179-180, and n. 10. In contrast, five Members of the Court read Jurek as not precluding a claim that, in a particular case, the jury was unable to fully consider the mitigating evidence introduced by a defendant in answering the special issues. 487 U.S., at 183 (O'CONNOR, J., concurring in judgment); id., at 199-200 (STEVENS, J., dissenting). Indeed, both the concurrence and the dissent understood Jurek as resting fundamentally on the express assurance that the special issues would permit the jury to fully consider all the mitigating evidence a defendant introduced that was relevant to the defendant's background and character and to the circumstances of the offense. Moreover, both the concurrence and the dissent stressed that "the right to have the sentencer consider and weigh relevant mitigating evidence would be meaningless unless the sentencer was also permitted to give effect to its consideration" in imposing sentence. 487 U.S., at 185 (O'CONNOR, J., concurring in judgment); id., at 199 (STEVENS, J., dissenting).

The concurrence in Franklin concluded that there was no Eighth Amendment violation in that case because Franklin's evidence of his good prison behavior had no clear relevance to his character other than to demonstrate his ability to live in a highly structured prison environment without endangering others. Thus, the jury was able to give effect to the mitigating force of this evidence in answering the second special issue. The concurrence noted, however:

"If . . . petitioner had introduced mitigating evidence about his background or character or the circumstances of the crime that was not relevant to the special verdict questions, or that had relevance to the defendant's moral culpability beyond the scope of the special verdict questions, the jury instructions would have provided the jury with no vehicle for expressing its 'reasoned moral response' to that evidence. If this were such a case, then we would have to decide whether the jury's inability to give effect to that evidence amounted to an Eighth Amendment violation." Id., at 185.

Penry argues that his mitigating evidence of mental retardation and childhood abuse has relevance to his moral culpability beyond the scope of the special issues, and that the jury was unable to express its "reasoned moral response" to that evidence in determining whether death was the appropriate punishment. We agree. Thus, we reject the State's contrary argument that the jury was able to consider and give effect to all of Penry's mitigating evidence in answering the special issues without any jury instructions on mitigating evidence.

The first special issue asks whether the defendant acted "deliberately and with the reasonable expectation that the death of the deceased . . . would result." Neither the Texas Legislature nor the Texas Court of Criminal Appeals have defined the term "deliberately," and the jury was not instructed on the term, so we do not know precisely what meaning the jury gave to it. Assuming, however, that the jurors in this case understood "deliberately" to mean something more than that Penry was guilty of "intentionally" committing murder, those jurors may still have been unable to give effect to Penry's mitigating evidence in answering the first special issue.

Penry's mental retardation was relevant to the question whether he was capable of acting "deliberately," but it also "had relevance to [his] moral culpability beyond the scope of the special verdict questio[n]." Franklin, supra, at 185. Personal culpability is not solely a function of a defendant's capacity to act "deliberately." A rational juror at the penalty phase of the trial could have concluded, in light of Penry's confession, that he deliberately killed Pamela Carpenter to escape detection. Because Penry was mentally retarded, however, and thus less able than a normal adult to control his impulses or to evaluate the consequences of his conduct, and because of his history of childhood abuse, that same juror could also conclude that Penry was less morally "culpable than defendants who have no such excuse," but who acted "deliberately" as that term is commonly understood. California v. Brown, 479 U.S., at 545 (O'CONNOR, J., concurring). See also Skipper v. South Carolina, 476 U.S. 1, 13-14 (1986) (Powell, J., concurring in judgment) (evidence concerning a defendant's "emotional history . . . bear[s] directly on the fundamental justice of imposing capital punishment").

In the absence of jury instructions defining "deliberately" in a way that would clearly direct the jury to consider fully Penry's mitigating evidence as it bears on his personal culpability, we cannot be sure that the jury was able to give effect to the mitigating evidence of Penry's mental retardation and history of abuse in answering the first special issue. Without such a special instruction, a juror who believed that Penry's retardation and background diminished his moral culpability and made imposition of the death penalty unwarranted would be unable to give effect to that conclusion if the juror also believed that Penry committed the crime "deliberately." Thus, we cannot be sure that the jury's answer to the first special issue reflected a "reasoned moral response" to Penry's mitigating evidence.

The second special issue asks "whether there is a probability that the defendant would commit criminal acts of violence that would constitute a continuing threat to society." The mitigating evidence concerning Penry's mental retardation indicated that one effect of his retardation is his inability to learn from his mistakes. Although this evidence is relevant to the second issue, it is relevant only as an aggravating factor because it suggests a "yes" answer to the question of future dangerousness. The prosecutor argued at the penalty hearing that there was "a very strong probability, based on the history of this defendant, his previous criminal record, and the psychiatric testimony that we've had in this case, that the defendant will continue to commit acts of this nature." App. 214. Even in a prison setting, the prosecutor argued, Penry could hurt doctors, nurses, librarians, or teachers who worked in the prison.

Penry's mental retardation and history of abuse is thus a two-edged sword: it may diminish his blameworthiness for his crime even as it indicates that there is a probability that he will be dangerous in the future. As Judge Reavley wrote for the Court of Appeals below:

"What was the jury to do if it decided that Penry, because of retardation, arrested emotional development and a troubled youth, should not be executed? If anything, the evidence made it more likely, not less likely, that the jury would answer the second question yes. It did not allow the jury to consider a major thrust of Penry's evidence as mitigating evidence." 832 F.2d, at 925 (footnote omitted) (emphasis in original).

The second special issue, therefore, did not provide a vehicle for the jury to give mitigating effect to Penry's evidence of mental retardation and childhood abuse.

The third special issue asks "whether the conduct of the defendant in killing the deceased was unreasonable in response to the provocation, if any, by the deceased." On this issue, the State argued that Penry stabbed Pamela Carpenter with a pair of scissors not in response to provocation, but "for the purpose of avoiding detection." App. 215. Penry's own confession indicated that he did not stab the victim after she wounded him superficially with a scissors during a struggle, but rather killed her after her struggle had ended and she was lying helpless. Even if a juror concluded that Penry's mental retardation and arrested emotional development rendered him less culpable for his crime than a normal adult, that would not necessarily diminish the "unreasonableness" of his conduct in response to "the provocation, if any, by the deceased." Thus, a juror who believed Penry lacked the moral culpability to be sentenced to death could not express that view in answering the third special issue if she also concluded that Penry's action was not a reasonable response to provocation.

The State contends, notwithstanding the three interrogatories, that Penry was free to introduce and argue the significance of his mitigating circumstances to the jury. In fact, defense counsel did argue that if a juror believed that Penry, because of the mitigating evidence of his mental retardation and abused background, did not deserve to be put to death, the juror should vote "no" on one of the special issues even if she believed the State had proved that the answer should be "yes." Thus, Penry's counsel stressed the evidence of Penry's mental retardation and abused background, and asked the jurors, "can you be proud to be a party to putting a man to death with that affliction?" App. 222. He urged the jury to answer the first special issue "no" because "it would be the just answer, and I think it would be a proper answer." Id., at 223. As for the prediction of the prosecution psychiatrist that Penry was likely to continue to get into trouble, the defense argued: "That may be true. But, a boy with this mentality, with this mental affliction, even though you have found that issue against us as to insanity, I don't think that there is any question in a single one of you juror's [sic] minds that there is something definitely wrong, basically, with this boy. And I think there is not a single one of you that doesn't believe that this boy had brain damage. . . ." Id., at 223-224. In effect, defense counsel urged the jury to "[t]hink about each of those special issues and see if you don't find that we're inquiring into the mental state of the defendant in each and every one of them." Id., at 221.

In rebuttal, the prosecution countered by stressing that the jurors had taken an oath to follow the law, and that they must follow the instructions they were given in answering the special issues:

"You've all taken an oath to follow the law and you know what the law is. . . . In answering these questions based on the evidence and following the law, and that's all that I asked you to do, is to go out and look at the evidence. The burden of proof is on the State as it has been from the beginning, and we accept that burden. And I honestly believe that we have more than met that burden, and that's the reason that you didn't hear Mr. Newman [defense attorney] argue. He didn't pick out these issues and point out to you where the State had failed to meet this burden. He didn't point out the weaknesses in the State's case because, ladies and gentlemen, I submit to you we've met our burden. . . . [Y]our job as jurors and your duty as jurors is not to act on your emotions, but to act on the law as the Judge has given it to you, and on the evidence that you have heard in this courtroom, then answer those questions accordingly." Id., at 225-226.

In light of the prosecutor's argument, and in the absence of appropriate jury instructions, a reasonable juror could well have believed that there was no vehicle for expressing the view that Penry did not deserve to be sentenced to death based upon his mitigating evidence.

The State conceded at oral argument in this Court that if a juror concluded that Penry acted deliberately and was likely to be dangerous in the future, but also concluded that because of his mental retardation he was not sufficiently culpable to deserve the death penalty, that juror would be unable to give effect to that mitigating evidence under the instructions given in this case. Tr. of Oral Arg. 38. The State contends, however, that to instruct the jury that it could render a discretionary grant of mercy, or say "no" to the death penalty, based on Penry's mitigating evidence, would be to return to the sort of unbridled discretion that led to Furman v. Georgia, 408 U.S. 238 (1972). We disagree.

To be sure, Furman held that "in order to minimize the risk that the death penalty would be imposed on a capriciously selected group of offenders, the decision to impose it had to be guided by standards so that the sentencing authority would focus on the particularized circumstances of the crime and the defendant." Gregg v. Georgia, 428 U.S. 153, 199 (1976) (joint opinion of Stewart, Powell, and STEVENS, JJ.). But as we made clear in Gregg, so long as the class of murderers subject to capital punishment is narrowed, there is no constitutional infirmity in a procedure that allows a jury to recommend mercy based on the mitigating evidence introduced by a defendant. Id., at 197-199, 203. As JUSTICE WHITE wrote in Gregg:

"The Georgia legislature has plainly made an effort to guide the jury in the exercise of its discretion, while at the same time permitting the jury to dispense mercy on the basis of factors too intangible to write into a statute, and I cannot accept the naked assertion that the effort is bound to fail. As the types of murders for which the death penalty may be imposed become more narrowly defined and are limited to those which are particularly serious or for which the death penalty is particularly appropriate as they are in Georgia by reason of the aggravating-circumstance requirement, it becomes reasonable to expect that juries — even given discretion not to impose the death penalty — will impose the death penalty in a substantial portion of the cases so defined. If they do, it can no longer be said that the penalty is being imposed wantonly and freakishly or so infrequently that it loses its usefulness as a sentencing device." Id., at 222 (opinion concurring in judgment).

"In contrast to the carefully defined standards that must narrow a sentencer's discretion to impose the death sentence, the Constitution limits a State's ability to narrow a sentencer's discretion to consider relevant evidence that might cause it to decline to impose the death sentence." McCleskey v. Kemp, 481 U.S. 279, 304 (1987) (emphasis in original). Indeed, it is precisely because the punishment should be directly related to the personal culpability of the defendant that the jury must be allowed to consider and give effect to mitigating evidence relevant to a defendant's character or record or the circumstances of the offense. Rather than creating the risk of an unguided emotional response, full consideration of evidence that mitigates against the death penalty is essential if the jury is to give a "'reasoned moral response to the defendant's background, character, and crime.'" Franklin, 487 U.S., at 184 (O'CONNOR, J., concurring in judgment) (quoting California v. Brown, 479 U.S., at 545 (O'CONNOR, J., concurring)). In order to ensure "reliability in the determination that death is the appropriate punishment in a specific case," Woodson, 428 U.S., at 305, the jury must be able to consider and give effect to any mitigating evidence relevant to a defendant's background and character or the circumstances of the crime.

In this case, in the absence of instructions informing the jury that it could consider and give effect to the mitigating evidence of Penry's mental retardation and abused background by declining to impose the death penalty, we conclude that the jury was not provided with a vehicle for expressing its "reasoned moral response" to that evidence in rendering its sentencing decision. Our reasoning in Lockett and Eddings thus compels a remand for resentencing so that we do not "risk that the death penalty will be imposed in spite of factors which may call for a less severe penalty." Lockett, 438 U.S., at 605; Eddings, 455 U.S., at 119 (O'CONNOR, J., concurring). "When the choice is between life and death, that risk is unacceptable and incompatible with the commands of the Eighth and Fourteenth Amendments." Lockett, supra, at 605.

IV

Penry's second claim is that it would be cruel and unusual punishment, prohibited by the Eighth Amendment, to execute a mentally retarded person like himself with the reasoning capacity of a 7-year-old. He argues that because of their mental disabilities, mentally retarded people do not possess the level of moral culpability to justify imposing the death sentence. He also argues that there is an emerging national consensus against executing the mentally retarded. The State responds that there is insufficient evidence of a national consensus against executing the retarded, and that existing procedural safeguards adequately protect the interests of mentally retarded persons such as Penry.

A

Under Teague, we address the retroactivity issue as a threshold matter because Penry is before us on collateral review. 489 U.S., at 310. If we were to hold that the Eighth Amendment prohibits the execution of mentally retarded persons such as Penry, we would be announcing a "new rule." Id., at 301. Such a rule is not dictated by precedent existing at the time Penry's conviction became final. Moreover, such a rule would "brea[k] new ground" and would impose a new obligation on the States and the Federal Government. Ibid. (citing Ford v. Wainwright, 477 U.S. 399, 410 (1986), which held that the Eighth Amendment prohibits the execution of insane persons, as a case announcing a new rule).

In Teague, we concluded that a new rule will not be applied retroactively to defendants on collateral review unless it falls within one of two exceptions. Under the first exception articulated by Justice Harlan, a new rule will be retroactive if it places "'certain kinds of primary, private individual conduct beyond the power of the criminal law-making authority to proscribe.'" Teague, supra, at 307 (quoting Mackey, 401 U.S., at 692 (Harlan, J., concurring in judgments in part and dissenting in part)). Although Teague read this exception as focusing solely on new rules according constitutional protection to an actor's primary conduct, Justice Harlan did speak in terms of substantive categorical guarantees accorded by the Constitution, regardless of the procedures followed. This Court subsequently held that the Eighth Amendment, as a substantive matter, prohibits imposing the death penalty on a certain class of defendants because of their status, Ford v. Wainwright, supra, at 410 (insanity), or because of the nature of their offense, Coker v. Georgia, 433 U.S. 584 (1977) (rape) (plurality opinion). In our view, a new rule placing a certain class of individuals beyond the State's power to punish by death is analogous to a new rule placing certain conduct beyond the State's power to punish at all. In both cases, the Constitution itself deprives the State of the power to impose a certain penalty, and the finality and comity concerns underlying Justice Harlan's view of retroactivity have little force. As Justice Harlan wrote: "There is little societal interest in permitting the criminal process to rest at a point where it ought properly never to repose." Mackey, supra, at 693. Therefore, the first exception set forth in Teague should be understood to cover not only rules forbidding criminal punishment of certain primary conduct but also rules prohibiting a certain category of punishment for a class of defendants because of their status or offense. Thus, if we held, as a substantive matter, that the Eighth Amendment prohibits the execution of mentally retarded persons such as Penry regardless of the procedures followed, such a rule would fall under the first exception to the general rule of nonretroactivity and would be applicable to defendants on collateral review. Accordingly, we address the merits of Penry's claim.

B

The Eighth Amendment categorically prohibits the infliction of cruel and unusual punishments. At a minimum, the Eighth Amendment prohibits punishment considered cruel and unusual at the time the Bill of Rights was adopted. Ford v. Wainwright, supra, at 405; Solem v. Helm, 463 U.S. 277, 285-286 (1983). The prohibitions of the Eighth Amendment are not limited, however, to those practices condemned by the common law in 1789. Ford, supra, at 406; Gregg v. Georgia, 428 U.S., at 171. The prohibition against cruel and unusual punishments also recognizes the "evolving standards of decency that mark the progress of a maturing society." Trop v. Dulles, 356 U.S. 86, 101 (1958) (plurality opinion); Ford, supra, at 406. In discerning those "evolving standards," we have looked to objective evidence of how our society views a particular punishment today. See Coker v. Georgia, supra, at 593-597; Enmund v. Florida, 458 U.S. 782, 788-796 (1982). The clearest and most reliable objective evidence of contemporary values is the legislation enacted by the country's legislatures. We have also looked to data concerning the actions of sentencing juries. Enmund, supra, at 794-796; Thompson v. Oklahoma, 487 U.S. 815, 831 (1988) (plurality opinion).

It was well settled at common law that "idiots," together with "lunatics," were not subject to punishment for criminal acts committed under those incapacities. As Blackstone wrote:

"The second case of a deficiency in will, which excuses from the guilt of crimes, arises also from a defective or vitiated understanding, viz. in an idiot or a lunatic. . . . [I]diots and lunatics are not chargeable for their own acts, if committed when under these incapacities: no, not even for treason itself. . . . [A] total idiocy, or absolute insanity, excuses from the guilt, and of course from the punishment, of any criminal action committed under such deprivation of the senses. . . ." 4 W. Blackstone, Commentaries *24 — *25 (emphasis in original).

See also 1 W. Hawkins, Pleas of the Crown 1-2 (7th ed. 1795) ("[T]hose who are under a natural disability of distinguishing between good and evil, as . . . ideots, and lunaticks are not punishable by any criminal prosecution whatsoever"). Idiocy was understood as "a defect of understanding from the moment of birth," in contrast to lunacy, which was "a partial derangement of the intellectual faculties, the senses returning at uncertain intervals." Id., at 2, n. 2.

There was no one definition of idiocy at common law, but the term "idiot" was generally used to describe persons who had a total lack of reason or understanding, or an inability to distinguish between good and evil. Hale wrote that a person who is deaf and mute from birth "is in presumption of law an ideot . . . because he hath no possibility to understand what is forbidden by law to be done, or under what penalties: but if it can appear, that he hath the use of understanding, . . . then he may be tried, and suffer judgment and execution." 1 M. Hale, Pleas of the Crown 34 (1736) (footnote omitted). See also id., at 29 (citing A. Fitzherbert, 2 Natura Brevium 233 (7th ed. 1730)); Trial of Edward Arnold, 16 How. St. Tr. 695, 765 (Eng. 1724) ("[A] man that is totally deprived of his understanding and memory, and doth not know what he is doing, no more than an infant, than a brute, or a wild beast, such a one is never the object of punishment"); S. Glueck, Mental Disorder and the Criminal Law 128-144 (1925).

The common law prohibition against punishing "idiots" and "lunatics" for criminal acts was the precursor of the insanity defense, which today generally includes "mental defect" as well as "mental disease" as part of the legal definition of insanity. See, e.g., American Law Institute, Model Penal Code § 4.01, p. 61 (1985) ("A person is not responsible for criminal conduct if at the time of such conduct as a result of mental disease or defect he lacks substantial capacity either to appreciate the criminality [wrongfulness] of his conduct or to conform his conduct to the requirements of law"); 18 U.S.C. § 17 (1982 ed., Supp. V) (it is an affirmative defense to federal prosecution if "the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts" at the time the offense was committed). See generally Ellis Luckasson, Mentally Retarded Criminal Defendants, 53 Geo. Wash. L. Rev. 414, 432-444 (1985).

In its emphasis on a permanent, congenital mental deficiency, the old common law notion of "idiocy" bears some similarity to the modern definition of mental retardation. Ellis Luckasson, supra, at 417. The common law prohibition against punishing "idiots" generally applied, however, to persons of such severe disability that they lacked the reasoning capacity to form criminal intent or to understand the difference between good and evil. In the 19th and early 20th centuries, the term "idiot" was used to describe the most retarded of persons, corresponding to what is called "profound" and "severe" retardation today. See AAMR, Classification in Mental Retardation 179 (H. Grossman ed. 1983); id., at 9 ("idiots" generally had IQ of 25 or below).

The common law prohibition against punishing "idiots" for their crimes suggests that it may indeed be "cruel and unusual" punishment to execute persons who are profoundly or severely retarded and wholly lacking the capacity to appreciate the wrongfulness of their actions. Because of the protections afforded by the insanity defense today, such a person is not likely to be convicted or face the prospect of punishment. See ABA Standards for Criminal Justice 7-9.1, commentary, p. 460 (2d ed. 1980) (most retarded people who reach the point of sentencing are mildly retarded). Moreover, under Ford v. Wainwright, 477 U.S. 399 (1986), someone who is "unaware of the punishment they are about to suffer and why they are to suffer it" cannot be executed. Id., at 422 (Powell, J., concurring in part and concurring in judgment).

Such a case is not before us today. Penry was found competent to stand trial. In other words, he was found to have the ability to consult with his lawyer with a reasonable degree of rational understanding, and was found to have a rational as well as factual understanding of the proceedings against him. Dusky v. United States, 362 U.S. 402 (1960); App. 20-24. In addition, the jury rejected his insanity defense, which reflected their conclusion that Penry knew that his conduct was wrong and was capable of conforming his conduct to the requirements of the law. Tex. Penal Code Ann. § 8.01(a) (1974 and Supp. 1989).

Penry argues, however, that there is objective evidence today of an emerging national consensus against execution of the mentally retarded, reflecting the "evolving standards of decency that mark the progress of a maturing society." Trop v. Dulles, 356 U.S., at 101. Brief for Petitioner 37-39. The federal Anti-Drug Abuse Act of 1988, Pub.L. 100-690, § 7001(1), 102 Stat. 4390, 21 U.S.C. § 848 (l) (1988 ed.), prohibits execution of a person who is mentally retarded. Only one State, however, currently bans execution of retarded persons who have been found guilty of a capital offense. Ga. Code Ann. § 17-7-131(j) (Supp. 1988). Maryland has enacted a similar statute which will take effect on July 1, 1989. Md. Ann. Code, Art. 27, § 412(f)(1) (1989).

In contrast, in Ford v. Wainwright, which held that the Eighth Amendment prohibits execution of the insane, considerably more evidence of a national consensus was available. No State permitted the execution of the insane, and 26 States had statutes explicitly requiring suspension of the execution of a capital defendant who became insane. Ford, 477 U.S., at 408, n. 2. Other States had adopted the common law prohibition against executing the insane. Ibid. Moreover, in examining the objective evidence of contemporary standards of decency in Thompson v. Oklahoma, the plurality noted that 18 States expressly established a minimum age in their death penalty statutes, and all of them required that the defendant have attained at least the age of 16 at the time of the offense. 487 U.S., at 829, and n. 30. In our view, the two state statutes prohibiting execution of the mentally retarded, even when added to the 14 States that have rejected capital punishment completely, do not provide sufficient evidence at present of a national consensus.

Penry does not offer any evidence of the general behavior of juries with respect to sentencing mentally retarded defendants, nor of decisions of prosecutors. He points instead to several public opinion surveys that indicate strong public opposition to execution of the retarded. For example, a poll taken in Texas found that 86% of those polled supported the death penalty, but 73% opposed its application to the mentally retarded. Reply Brief for Petitioner 6-7; Austin American Statesman, November 15, 1988, p. B3. A Florida poll found 71% of those surveyed were opposed to the execution of mentally retarded capital defendants, while only 12% were in favor. Brief for Petitioner 38; App. 279. A Georgia poll found 66% of those polled opposed to the death penalty for the retarded, 17% in favor, with 16% responding that it depends how retarded the person is. Brief for Petitioner 38; App. 283. In addition, the AAMR, the country's oldest and largest organization of professionals working with the mentally retarded, opposes the execution of persons who are mentally retarded. AAMR, Resolution on Mental Retardation and the Death Penalty, January 1988, App. to Brief for American Association on Mental Retardation et al. as Amici Curiae 1a-2a (hereafter Amici Brief for AAMR et al.). The public sentiment expressed in these and other polls and resolutions may ultimately find expression in legislation, which is an objective indicator of contemporary values upon which we can rely. But at present, there is insufficient evidence of a national consensus against executing mentally retarded people convicted of capital offenses for us to conclude that it is categorically prohibited by the Eighth Amendment.

C

Relying largely on objective evidence such as the judgments of legislatures and juries, we have also considered whether application of the death penalty to particular categories of crimes or classes of offenders violates the Eighth Amendment because it "makes no measurable contribution to acceptable goals of punishment and hence is nothing more than the purposeless and needless imposition of pain and suffering" or because it is "grossly out of proportion to the severity of the crime." Coker v. Georgia, 433 U.S., at 592 (plurality opinion); Thompson v. Oklahoma, 487 U.S., at 833 (plurality opinion); Tison v. Arizona, 481 U.S. 137 (1987); Enmund v. Florida, 458 U.S., at 798-801. Gregg noted that "[t]he death penalty is said to serve two principal social purposes: retribution and deterrence of capital crimes by prospective offenders." Gregg v. Georgia, 428 U.S., at 183 (joint opinion of Stewart, Powell, and STEVENS, JJ.). "The heart of the retribution rationale is that a criminal sentence must be directly related to the personal culpability of the criminal offender." Tison v. Arizona, supra, at 149. See also Enmund, supra, at 825 (O'CONNOR, J., dissenting) (the Eighth Amendment concept of "proportionality requires a nexus between the punishment imposed and the defendant's blameworthiness").

Penry argues that execution of a mentally retarded person like himself with a reasoning capacity of approximately a 7-year-old would be cruel and unusual because it is disproportionate to his degree of personal culpability. Brief for Petitioner 49-50. Just as the plurality in Thompson reasoned that a juvenile is less culpable than an adult for the same crime, 487 U.S., at 835, Penry argues that mentally retarded people do not have the judgment, perspective, and self-control of a person of normal intelligence. In essence, Penry argues that because of his diminished ability to control his impulses, to think in long-range terms, and to learn from his mistakes, he "is not capable of acting with the degree of culpability that can justify the ultimate penalty," id., at 823.

The AAMR and other groups working with the mentally retarded agree with Penry. They argue as amici that all mentally retarded people, regardless of their degree of retardation, have substantial cognitive and behavioral disabilities that reduce their level of blameworthiness for a capital offense. Amici Brief for AAMR et al. 5-9, 13-15. Amici do not argue that people with mental retardation cannot be held responsible or punished for criminal acts they commit. Rather, they contend that because of "disability in the areas of cognitive impairment, moral reasoning, control of impulsivity, and the ability to understand basic relationships between cause and effect," mentally retarded people cannot act with the level of moral culpability that would justify imposition of the death sentence. Id., at 4. Thus, in their view, execution of mentally retarded people convicted of capital offenses serves no valid retributive purpose. Id., at 19.

It is clear that mental retardation has long been regarded as a factor that may diminish an individual's culpability for a criminal act. See supra, at 331-333; ABA Standards for Criminal Justice 7-9.3, commentary, at 463; State v. Hall, 176 Neb. 295, 310, 125 N.W.2d 918, 927 (1964). See generally Ellis Luckasson, 53 Geo. Wash.L.Rev., at 414. In its most severe forms, mental retardation may result in complete exculpation from criminal responsibility. Moreover, virtually all of the States with death penalty statutes that list statutory mitigating factors include as a mitigating circumstance evidence that "[t]he capacity of the defendant to appreciate the criminality of his conduct or to conform his conduct to the requirements of law was substantially impaired." A number of States explicitly mention "mental defect" in connection with such a mitigating circumstance. Indeed, as the Court holds in Part III of this opinion, the sentencing body must be allowed to consider mental retardation as a mitigating circumstance in making the individualized determination whether death is the appropriate punishment in a particular case.

On the record before the Court today, however, I cannot conclude that all mentally retarded people of Penry's ability — by virtue of their mental retardation alone, and apart from any individualized consideration of their personal responsibility — inevitably lack the cognitive, volitional, and moral capacity to act with the degree of culpability associated with the death penalty. Mentally retarded persons are individuals whose abilities and experiences can vary greatly. As the AAMR's standard work, Classification in Mental Retardation, points out:

"The term mental retardation, as commonly used today, embraces a heterogeneous population, ranging from totally dependent to nearly independent people. Although all individuals so designated share the common attributes of low intelligence and inadequacies in adaptive behavior, there are marked variations in the degree of deficit manifested and the presence or absence of associated physical handicaps, stigmata, and psychologically disordered states." Classification in Mental Retardation, at 12.

In addition to the varying degrees of mental retardation, the consequences of a retarded person's mental impairment, including the deficits in his or her adaptive behavior, "may be ameliorated through education and habilitation." Ellis Luckasson, supra, at 424, n. 54. Although retarded persons generally have difficulty learning from experience, Amici Brief for AAMR et al. 7, some are fully "capable of learning, working, and living in their communities." Id., at 6. See American Association on Mental Deficiency, Monograph 6, Lives in Process: Mildly Retarded Adults in a Large City (R. Edgerton ed. 1984). In light of the diverse capacities and life experiences of mentally retarded persons, it cannot be said on the record before us today that all mentally retarded people, by definition, can never act with the level of culpability associated with the death penalty.

Penry urges us to rely on the concept of "mental age," and to hold that execution of any person with a mental age of seven or below would constitute cruel and unusual punishment. Tr. of Oral Arg. 22-25. Mental age is "calculated as the chronological age of nonretarded children whose average IQ test performance is equivalent to that of the individual with mental retardation." Amici Brief for AAMR et al. 14, n. 6. See D. Wechsler, The Measurement and Appraisal of Adult Intelligence 24-25 (4th ed. 1958). Such a rule should not be adopted today. First, there was no finding below by the judge or jury concerning Penry's "mental age." One of Penry's expert witnesses, Dr. Brown, testified that he estimated Penry's "mental age" to be 6 1/2. App. 41. That same expert estimated that Penry's "social maturity" was that of a 9- or 10-year-old. Ibid. As a more general matter, the "mental age" concept, irrespective of its intuitive appeal, is problematic in several respects. As the AAMR acknowledges, "[t]he equivalence between nonretarded children and retarded adults is, of course, imprecise." Amici Brief for AAMR et al. 14, n. 6. The "mental age" concept may underestimate the life experiences of retarded adults, while it may overestimate the ability of retarded adults to use logic and foresight to solve problems. Ibid. The mental age concept has other limitations as well. Beyond the chronological age of 15 or 16, the mean scores on most intelligence tests cease to increase significantly with age. Wechsler 26. As a result, "[t]he average mental age of the average 20 year old is not 20 but 15 years." Id., at 27. See also In re Ramon M., 22 Cal.3d 419, 429, 584 P.2d 524, 531 (1978) ("[T]he 'mental age' of the average adult under present norms is approximately 16 years and 8 months").

Not surprisingly, courts have long been reluctant to rely on the concept of mental age as a basis for exculpating a defendant from criminal responsibility. See, e.g., In re Ramon M., supra, at 429, 584 P.2d, at 531; State v. Schilling, 95 N.J.L. 145, 148, 112 A. 400, 402 (1920); People v. Marquis, 344 Ill. 261, 267, 176 N.E. 314, 316 (1931); Chriswell v. State, 171 Ark. 255, 259, 283 S.W. 981, 983 (1926). Cf. Pickett v. State, 71 So.2d 102, 107 (Ala. 1954). See generally Ellis Luckasson, 53 Geo. Wash. L. Rev., at 435. Moreover, reliance on mental age to measure the capabilities of a retarded person for purposes of the Eighth Amendment could have a disempowering effect if applied in other areas of the law. Thus, on that premise, a mildly mentally retarded person could be denied the opportunity to enter into contracts or to marry by virtue of the fact that he had a "mental age" of a young child. In light of the inherent problems with the mental age concept, and in the absence of better evidence of a national consensus against execution of the retarded, mental age should not be adopted as a line-drawing principle in our Eighth Amendment jurisprudence.

In sum, mental retardation is a factor that may well lessen a defendant's culpability for a capital offense. But we cannot conclude today that the Eighth Amendment precludes the execution of any mentally retarded person of Penry's ability convicted of a capital offense simply by virtue of his or her mental retardation alone. So long as sentencers can consider and give effect to mitigating evidence of mental retardation in imposing sentence, an individualized determination whether "death is the appropriate punishment" can be made in each particular case. While a national consensus against execution of the mentally retarded may someday emerge reflecting the "evolving standards of decency that mark the progress of a maturing society," there is insufficient evidence of such a consensus today.

Accordingly, the judgment below is affirmed in part and reversed in part, and the case is remanded for further proceedings consistent with this opinion.

It is so ordered.