CLARK v. ARIZONA

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CLARK v. ARIZONA
certiorari to the court of appeals of arizona
No. 05–5966. Argued April 19, 2006—Decided June 29, 2006
Petitioner Clark was charged with first-degree murder under an Arizona
statute prohibiting “[i]nten[tionally] or knowing[ly]” killing a police of
ficer in the line of duty. At his bench trial, Clark did not contest that he
shot the officer or that the officer died, but relied on his own undisputed
paranoid schizophrenia at the time of the incident to deny that he had
the specific intent to shoot an officer or knowledge that he was doing so.
Accordingly, the prosecutor offered circumstantial evidence that Clark
knew the victim was a police officer and testimony indicating that Clark
had previously stated he wanted to shoot police and had lured the victim
to the scene to kill him. In presenting the defense case, Clark claimed
mental illness, which he sought to introduce for two purposes. First,
he raised the affirmative defense of insanity, putting the burden on him
self to prove by clear and convincing evidence that, in the words of
another state statute, “at the time of the [crime, he] was afflicted with
a mental disease or defect of such severity that [he] did not know the
criminal act was wrong.” Second, he aimed to rebut the prosecution’s
evidence of the requisite mens rea, that he had acted intentionally or
knowingly to kill an officer.
Ruling that Clark could not rely on evidence bearing on insanity to
dispute the mens rea, the trial court cited the Arizona Supreme Court’s
decision in State v. Mott, 187 Ariz. 536, 931 P. 2d 1046, which refused to
allow psychiatric testimony to negate specific intent and held that Ari
zona does not allow evidence of a mental disorder short of insanity to
negate the mens rea element of a crime. As to his insanity, then, Clark
presented lay testimony describing his increasingly bizarre behavior
over the year before the shooting. Other lay and expert testimony indi
cated, among other things, that Clark thought that “aliens” (some imper
sonating government agents) were trying to kill him and that bullets
were the only way to stop them. A psychiatrist testified that Clark
was suffering from paranoid schizophrenia with delusions about “aliens”
when he killed the officer, and concluded that Clark was incapable of
luring the officer or understanding right from wrong and was thus in
sane at the time of the killing. In rebuttal, the State’s psychiatrist
gave his opinion that Clark’s paranoid schizophrenia did not keep him
from appreciating the wrongfulness of his conduct before and after the
shooting. The judge then issued a first-degree murder verdict, finding

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that in light of the facts of the crime, the expert evaluations, Clark’s
actions and behavior both before and after the shooting, and the obser
vations of those who knew him, Clark had not established that his
schizophrenia distorted his perception of reality so severely that he did
not know his actions were wrong.
Clark moved to vacate the judgment and life sentence, arguing,
among other things, that Arizona’s insanity test and its Mott rule each
violate due process. He claimed that the Arizona Legislature had im
permissibly narrowed its insanity standard in 1993 when it eliminated
the first of the two parts of the traditional M’Naghten insanity test.
The trial court denied the motion. Affirming, the Arizona Court of Ap
peals held, among other things, that the State’s insanity scheme was
consistent with due process. The court read Mott as barring the trial
court’s consideration of evidence of Clark’s mental illness and capacity
directly on the element of mens rea.
Held:
1. Due process does not prohibit Arizona’s use of an insanity test
stated solely in terms of the capacity to tell whether an act charged as
a crime was right or wrong. Pp. 747–756.
(a) The first part of the landmark English rule in M’Naghten’s Case
asks about cognitive capacity: whether a mental defect leaves a defend
ant unable to understand what he was doing. The second part presents
an ostensibly alternative basis for recognizing a defense of insanity un
derstood as a lack of moral capacity: whether a mental disease or defect
leaves a defendant unable to understand that his action was wrong. Al
though the Arizona Legislature at first adopted the full M’Naghten
statement, it later dropped the cognitive incapacity part. Under cur
rent Arizona law, a defendant will not be adjudged insane unless he
demonstrates that at the time of the crime, he was afflicted with a men
tal disease or defect of such severity that he did not know the criminal
act was wrong. Pp. 747–748.
(b) Clark insists that the side-by-side M’Naghten test represents
the minimum that a government must provide, and he argues that elimi
nating the first part “ ‘offends [a] principle of justice so rooted in the
traditions and conscience of our people as to be ranked as fundamen
tal,’ ” Patterson v. New York, 432 U. S. 197, 202. The claim entails no
light burden, and Clark does not carry it. History shows no deference
to M’Naghten that could elevate its formula to the level of fundamental
principle, so as to limit the traditional recognition of a State’s capacity
to define crimes and defenses. See, e. g., Patterson, supra, at 210.
Even a cursory examination of the traditional Anglo-American ap
proaches to insanity reveals significant differences among them, with

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four traditional strains variously combined to yield a diversity of Ameri
can standards. Although 17 States and the Federal Government have
adopted recognizable versions of the M’Naghten test with both its com
ponents, other States have adopted a variety of standards based on all
or part of one or more of four variants. The alternatives are multiplied
further by variations in the prescribed insanity verdict. This varied
background makes clear that no particular formulation has evolved into
a baseline for due process, and that the insanity rule, like the concep
tualization of criminal offenses, is substantially open to state choice.
Pp. 748–753.
(c) Nor does Arizona’s abbreviation of the M’Naghten statement
raise a proper claim that some constitutional minimum has been short
changed. Although Arizona’s former statement of the full M’Naghten
rule was constitutionally adequate, the abbreviated rule is no less so,
for cognitive incapacity is relevant under that statement, just as it was
under the more extended formulation, and evidence going to cognitive
incapacity has the same significance under the short form as it had
under the long. Though Clark is correct that applying the moral inca
pacity test (telling right from wrong) does not necessarily require evalu
ation of a defendant’s cognitive capacity to appreciate the nature and
quality of the acts charged against him, his argument fails to recognize
that cognitive incapacity is itself enough to demonstrate moral incapac
ity, so that evidence bearing on whether the defendant knew the nature
and quality of his actions is both relevant and admissible. In practical
terms, if a defendant did not know what he was doing when he acted,
he could not have known that he was performing the wrongful act
charged as a crime. The Arizona appeals court acknowledged as much
in this case. Clark adopted this very analysis in the trial court, which
apparently agreed when it admitted his cognitive incapacity evidence
for consideration under the State’s moral incapacity formulation. Clark
can point to no evidence bearing on insanity that was excluded.
Pp. 753–756.
2. The Arizona Supreme Court’s Mott rule does not violate due proc
ess. Pp. 756–779.
(a) Mott held that testimony of a professional psychologist or psy
chiatrist about a defendant’s mental incapacity owing to mental disease
or defect was admissible, and could be considered, only for its bearing
on an insanity defense, but could not be considered on the element of
mens rea. Of the three categories of evidence that potentially bear on
mens rea—(1) everyday “observation evidence” either by lay or expert
witnesses of what Clark did or said, which may support the professional
diagnoses of disease and in any event is the kind of evidence that can
be relevant to show what was on Clark’s mind when he fired his gun;

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(2) “mental-disease evidence,” typically from professional psychologists
or psychiatrists based on factual reports, professional observations, and
tests about Clark’s mental disease, with features described by the wit
ness; and (3) “capacity evidence,” typically by the same experts, about
Clark’s capacity for cognition and moral judgment (and ultimately also
his capacity to form mens rea)—Mott imposed no restriction on consid
ering evidence of the first sort, but applies to the latter two. Although
the trial court seems to have applied the Mott restriction to all three
categories of evidence Clark offered for the purpose of showing what he
called his inability to form the required mens rea, his objection to Mott’s
application does not turn on the distinction between lay and expert wit
nesses or the kinds of testimony they were competent to present.
Rather, the issue here is Clark’s claim that the Mott rule violates due
process. Pp. 756–765.
(b) Clark’s Mott challenge turns on the application of the presump
tion of innocence in criminal cases, the presumption of sanity, and the
principle that a criminal defendant is entitled to present relevant and
favorable evidence on an element of the offense charged against him.
Pp. 765–771.
(i) The presumption of innocence is that a defendant is innocent
unless and until the government proves beyond a reasonable doubt each
element of the offense charged, including the mental element or mens
rea. The modern tendency is to describe the mens rea required to
prove particular offenses in specific terms, as shown in the Arizona stat
ute requiring the State to prove that in acting to kill the victim, Clark
intended to kill a law enforcement officer on duty or knew that the
victim was such an officer on duty. As applied to mens rea (and every
other element), the force of the presumption of innocence is measured
by the force of the showing needed to overcome it, which is proof beyond
a reasonable doubt that a defendant’s state of mind was in fact what the
charge states. See In re Winship, 397 U. S. 358, 361–363. P. 766.
(ii) The presumption of sanity dispenses with a requirement that
the government include as an element of every criminal charge an alle
gation that the defendant had the capacity to form the mens rea neces
sary for conviction and criminal responsibility. Unlike the presumption
of innocence, the presumption of sanity’s force varies across the many
state and federal jurisdictions, and prior law has recognized consider
able leeway on the part of the legislative branch in defining the pre
sumption’s strength through the kind of evidence and degree of persua
siveness necessary to overcome it, see Fisher v. United States, 328 U. S.
463, 466–476. There are two points where the sanity or capacity pre
sumption may be placed in issue. First, a State may allow a defendant
to introduce (and a factfinder to consider) evidence of mental disease or

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incapacity for the bearing it can have on the government’s burden to
show mens rea. Second, the sanity presumption’s force may be tested
in the consideration of an insanity defense raised by a defendant. In
sanity rules like M’Naghten and the variants noted above are attempts
to define or indicate the kinds of mental differences that overcome the
presumption of sanity or capacity and therefore excuse a defendant from
customary criminal responsibility, see, e. g., Jones v. United States, 463
U. S. 354, 373, n. 4, even if the prosecution has otherwise overcome the
presumption of innocence by convincing the factfinder of all the ele
ments charged beyond a reasonable doubt. The burden a defendant
raising the insanity issue must carry defines the strength of the sanity
presumption. A State may, for example, place the burden of persuasion
on a defendant to prove insanity as the applicable law defines it, whether
by a preponderance of the evidence or to some more convincing degree.
See, e. g., Leland v. Oregon, 343 U. S. 790, 798. Pp. 766–769.
(iii) A defendant has a due process right to present evidence fa
vorable to himself on an element that must be proven to convict him.
Evidence tending to show that a defendant suffers from mental disease
and lacks capacity to form mens rea is relevant to rebut evidence that
he did in fact form the required mens rea at the time in question. Thus,
Clark claims a right to require the factfinder in this case to consider
testimony about his mental illness and his incapacity directly, when
weighing the persuasiveness of other evidence tending to show mens
rea, which the prosecution has the burden to prove. However, the right
to introduce relevant evidence can be curtailed if there is a good reason
for doing so. For example, trial judges may “exclude evidence if its
probative value is outweighed by certain other factors such as unfair
prejudice, confusion of the issues, or potential to mislead the jury.”
Holmes v. South Carolina, 547 U. S. 319, 326. And if evidence may be
kept out entirely, its consideration may be subject to limitation, which
Arizona claims the power to impose here. Under state law, mental
disease and capacity evidence may be considered only for its bearing on
the insanity defense, and it will avail a defendant only if it is persuasive
enough to satisfy the defendant’s burden as defined by the terms of that
defense. Such evidence is thus being channeled or restricted to one
issue; it is not being excluded entirely, and the question is whether rea
sons for requiring it to be channeled and restricted satisfy due process’s
fundamental fairness standard. Pp. 769–771.
(c) The reasons supporting the Arizona rule satisfy due process.
Pp. 771–778.
(i) The first such reason is Arizona’s authority to define its pre
sumption of sanity (or capacity or responsibility) by choosing an insanity
definition and placing the burden of persuasion on criminal defendants

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claiming incapacity as an excuse. Consistent with due process, a State
can require defendants to bear that burden, see Leland, supra, at 797–
799, and Clark does not object to Arizona’s decision to require persua
sion to a clear and convincing degree before the presumption of sanity
and normal responsibility is overcome. If a State is to have this author
ity in practice as well as in theory, it must be able to deny a defendant
the opportunity to displace the sanity presumption more easily when
addressing a different issue during the criminal trial. Yet just such an
opportunity would be available if expert testimony of mental disease
and incapacity could be considered for whatever a factfinder might think
it was worth on the mens rea issue. The sanity presumption would
then be only as strong as the evidence a factfinder would accept as
enough to raise a reasonable doubt about mens rea; once reasonable
doubt was found, acquittal would be required, and the standards estab
lished for the insanity defense would go by the boards. What counts
for due process is simply that a State wishing to avoid a second avenue
for exploring capacity, less stringent for a defendant, has a good reason
for confining the consideration of mental-disease and incapacity evidence
to the insanity defense. Pp. 771–773.
(ii) Arizona’s rule also serves to avoid confusion and misunder
standing on the part of jurors. The controversial character of some
categories of mental disease, the potential of mental-disease evidence to
mislead, and the danger of according greater certainty to capacity evi
dence than experts claim for it give rise to risks that may reasonably
be hedged by channeling the consideration of such evidence to the insan
ity issue on which, in States like Arizona, a defendant has the burden
of persuasion. First, the diagnosis may mask vigorous debate within
the psychiatric profession about the very contours of the mental disease
itself. See, e. g., Jones, supra, at 364–365, n. 13. Though mental
disease evidence is certainly not condemned wholesale, the consequence
of this professional ferment is a general caution in treating psychological
classifications as predicates for excusing otherwise criminal conduct.
Next, there is the potential of mental-disease evidence to mislead jurors
(when they are the factfinders) through the power of this kind of evi
dence to suggest that a defendant suffering from a recognized mental
disease lacks cognitive, moral, volitional, or other capacity, when that
may not be a sound conclusion at all. Even when a category of mental
disease is broadly accepted and the assignment of a defendant’s behavior
to that category is uncontroversial, the classification may suggest some
thing very significant about a defendant’s capacity, when in fact the clas
sification tells little or nothing about the defendant’s ability to form
mens rea or to exercise the cognitive, moral, or volitional capacities that
define legal sanity. The limits of the utility of a professional disease

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diagnosis are evident in the dispute between the two testifying experts
in this case; they agree that Clark was schizophrenic, but they reach
opposite conclusions on whether his mental disease left him bereft of
cognitive or moral capacity. Finally, there are particular risks inherent
in the opinions of the experts who supplement the mental-disease classi
fications with opinions on incapacity: on whether the mental disease ren
dered a particular defendant incapable of the cognition necessary for
moral judgment or mens rea or otherwise incapable of understanding
the wrongfulness of the conduct charged. Unlike observational evi
dence bearing on mens rea, capacity evidence consists of judgment, and
judgment is fraught with multiple perils. Although such capacity judg
ments may be given in the utmost good faith, their potentially tenuous
character is indicated by the candor of the defense expert in this very
case. He testified that Clark lacked the capacity to appreciate the cir
cumstances realistically and to understand the wrongfulness of what he
was doing, but he admitted that no one knew exactly what was on
Clark’s mind at the time of the shooting. Even when an expert is con
fident that his understanding of the mind is reliable, judgment address
ing the basic categories of capacity requires a leap from the concepts of
psychology, which are devised for thinking about treatment, to the con
cepts of legal sanity, which are devised for thinking about criminal re
sponsibility. Pp. 773–778.
(d) For these reasons, there is also no cause to claim that channeling
evidence on mental disease and capacity offends any “ ‘principle of jus
tice so rooted in the traditions and conscience of our people as to be
ranked as fundamental,’ ” Patterson, 432 U. S., at 202. P. 779.
Affirmed.
Souter, J., delivered the opinion of the Court, in which Roberts, C. J.,
and Scalia, Thomas, and Alito, JJ., joined, and in which Breyer, J.,
joined except as to Parts III–B and III–C and the ultimate disposition.
Breyer, J., filed an opinion concurring in part and dissenting in part, post,
p. 779. Kennedy, J., filed a dissenting opinion, in which Stevens and
Ginsburg, JJ., joined, post, p. 781.
David Goldberg, by appointment of the Court, 547 U. S.
1017, argued the cause and filed briefs for petitioner.
Randall M. Howe argued the cause for respondent. With
him on the brief were Terry Goddard, Attorney General
of Arizona, Mary O’Grady, Solicitor General, and Michael
O’Toole, Assistant Attorney General.

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Solicitor General Clement argued the cause for the
United States as amicus curiae urging affirmance. With
him on the brief were Assistant Attorney General Fisher,
Deputy Solicitor General Dreeben, Matthew D. Roberts, and
Kirby A. Heller.*
Justice Souter delivered the opinion of the Court.
The case presents two questions: whether due process pro
hibits Arizona’s use of an insanity test stated solely in terms
of the capacity to tell whether an act charged as a crime was
right or wrong; and whether Arizona violates due process in
restricting consideration of defense evidence of mental ill
ness and incapacity to its bearing on a claim of insanity, thus
eliminating its significance directly on the issue of the mental
element of the crime charged (known in legal shorthand as
the mens rea, or guilty mind). We hold that there is no
violation of due process in either instance.
*Briefs of amici curiae urging reversal were filed for the American
Association on Mental Retardation et al. by James W. Ellis, Michael B.
Browde, and Richard A. Gonzales; and for the American Psychiatric Asso
ciation et al. by Richard G. Taranto, David W. Ogden, and Nathalie F. P.
Gilfoyle.
A brief of amici curiae urging affirmance was filed for the Common
wealth of Massachusetts et al. by Thomas F. Reilly, Attorney General of
Massachusetts, David M. Lieber, Assistant Attorney General, and Dan
Schweitzer, and by the Attorneys General for their respective States as
follows: Troy King of Alabama, Mike Beebe of Arkansas, John W. Suthers
of Colorado, Carl C. Danberg of Delaware, Mark J. Bennett of Hawaii,
Steve Carter of Indiana, Michael A. Cox of Michigan, Mike McGrath of
Montana, Jim Petro of Ohio, W. A. Drew Edmondson of Oklahoma, Hardy
Myers of Oregon, Thomas W. Corbett, Jr., of Pennsylvania, Henry D. Mc-
Master of South Carolina, Lawrence E. Long of South Dakota, and Greg
Abbott of Texas.
Briefs of amici curiae were filed for the Citizens Commission on Human
Rights by Kendrick Moxon; and for the Treatment Advocacy Center by
David A. Kotler and Megan Elizabeth Zavieh.

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I
In the early hours of June 21, 2000, Officer Jeffrey Moritz
of the Flagstaff Police responded in uniform to complaints
that a pickup truck with loud music blaring was circling a
residential block. When he located the truck, the officer
turned on the emergency lights and siren of his marked pa
trol car, which prompted petitioner Eric Clark, the truck’s
driver (then 17), to pull over. Officer Moritz got out of the
patrol car and told Clark to stay where he was. Less than
a minute later, Clark shot the officer, who died soon after
but not before calling the police dispatcher for help. Clark
ran away on foot but was arrested later that day with gun
powder residue on his hands; the gun that killed the officer
was found nearby, stuffed into a knit cap.
Clark was charged with first-degree murder under Ariz.
Rev. Stat. Ann. § 13–1105(A)(3) (West Supp. 2005) for inten
tionally or knowingly killing a law enforcement officer in the
line of duty.1 In March 2001, Clark was found incompetent
to stand trial and was committed to a state hospital for treat
ment, but two years later the same trial court found his com
petence restored and ordered him to be tried. Clark waived
his right to a jury, and the case was heard by the court.
At trial, Clark did not contest the shooting and death, but
relied on his undisputed paranoid schizophrenia at the time
of the incident in denying that he had the specific intent to
shoot a law enforcement officer or knowledge that he was
doing so, as required by the statute. Accordingly, the prose
cutor offered circumstantial evidence that Clark knew Officer
Moritz was a law enforcement officer. The evidence showed
that the officer was in uniform at the time, that he caught
1 Section 13–1105(A)(3) provides that “[a] person commits first degree
murder if . . . [i]ntending or knowing that the person’s conduct will cause
death to a law enforcement officer, the person causes the death of a law
enforcement officer who is in the line of duty.”

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up with Clark in a marked police car with emergency lights
and siren going, and that Clark acknowledged the symbols of
police authority and stopped. The testimony for the prose
cution indicated that Clark had intentionally lured an officer
to the scene to kill him, having told some people a few weeks
before the incident that he wanted to shoot police officers.
At the close of the State’s evidence, the trial court denied
Clark’s motion for judgment of acquittal for failure to prove
intent to kill a law enforcement officer or knowledge that
Officer Moritz was a law enforcement officer.
In presenting the defense case, Clark claimed mental ill
ness, which he sought to introduce for two purposes. First,
he raised the affirmative defense of insanity, putting the bur
den on himself to prove by clear and convincing evidence,
§ 13–502(C) (West 2001), that “at the time of the commission
of the criminal act [he] was afflicted with a mental disease
or defect of such severity that [he] did not know the criminal
act was wrong,” § 13–502(A).2 Second, he aimed to rebut
the prosecution’s evidence of the requisite mens rea, that he
had acted intentionally or knowingly to kill a law enforce
ment officer. See, e. g., Record in No. CR 2000–538 (Ariz.
Super. Ct.), Doc. 374 (hereinafter Record).
2 Section 13–502(A) provides in full that
“A person may be found guilty except insane if at the time of the commis
sion of the criminal act the person was afflicted with a mental disease or
defect of such severity that the person did not know the criminal act was
wrong. A mental disease or defect constituting legal insanity is an af
firmative defense. Mental disease or defect does not include disorders
that result from acute voluntary intoxication or withdrawal from alcohol
or drugs, character defects, psychosexual disorders or impulse control dis
orders. Conditions that do not constitute legal insanity include but are
not limited to momentary, temporary conditions arising from the pressure
of the circumstances, moral decadence, depravity or passion growing out
of anger, jealousy, revenge, hatred or other motives in a person who does
not suffer from a mental disease or defect or an abnormality that is mani
fested only by criminal conduct.”
A defendant found “guilty except insane” is committed to a state
mental-health facility for treatment. See § 13–502(D).

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The trial court ruled that Clark could not rely on evidence
bearing on insanity to dispute the mens rea. The court
cited State v. Mott, 187 Ariz. 536, 931 P. 2d 1046, cert. denied,
520 U. S. 1234 (1997), which “refused to allow psychiatric tes
timony to negate specific intent,” 187 Ariz., at 541, 931 P. 2d,
at 1051, and held that “Arizona does not allow evidence of a
defendant’s mental disorder short of insanity . . . to negate
the mens rea element of a crime,” ibid.3
As to his insanity, then, Clark presented testimony from
classmates, school officials, and his family describing his in
creasingly bizarre behavior over the year before the shoot
ing. Witnesses testified, for example, that paranoid delu
sions led Clark to rig a fishing line with beads and wind
chimes at home to alert him to intrusion by invaders, and to
keep a bird in his automobile to warn of airborne poison.
There was lay and expert testimony that Clark thought
Flagstaff was populated with “aliens” (some impersonating
government agents), the “aliens” were trying to kill him, and
bullets were the only way to stop them. A psychiatrist tes
tified that Clark was suffering from paranoid schizophrenia
with delusions about “aliens” when he killed Officer Moritz,
and he concluded that Clark was incapable of luring the offi
cer or understanding right from wrong and that he was thus
insane at the time of the killing. In rebuttal, a psychiatrist
for the State gave his opinion that Clark’s paranoid schizo
phrenia did not keep him from appreciating the wrongfulness
of his conduct, as shown by his actions before and after the
shooting (such as circling the residential block with music
blaring as if to lure the police to intervene, evading the police
after the shooting, and hiding the gun).
At the close of the defense case consisting of this evidence
bearing on mental illness, the trial court denied Clark’s re
3 The trial court permitted Clark to introduce this evidence, whether
primarily going to insanity or lack of intent, “because it goes to the insan
ity issue and because we’re not in front of a jury.” App. 9. It also al
lowed him to make an offer of proof as to intent to preserve the issue on
appeal. Ibid.

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newed motion for a directed verdict grounded on failure of
the prosecution to show that Clark knew the victim was a
police officer.4 The judge then issued a special verdict of
first-degree murder, expressly finding that Clark shot and
caused the death of Officer Moritz beyond a reasonable doubt
and that Clark had not shown that he was insane at the time.
The judge noted that though Clark was indisputably afflicted
with paranoid schizophrenia at the time of the shooting, the
mental illness “did not . . . distort his perception of reality
so severely that he did not know his actions were wrong.”
App. 334. For this conclusion, the judge expressly relied on
“the facts of the crime, the evaluations of the experts,
[Clark’s] actions and behavior both before and after the
shooting, and the observations of those that knew [Clark].”
Id., at 333. The sentence was life imprisonment without the
possibility of release for 25 years.
Clark moved to vacate the judgment and sentence, ar
guing, among other things, that Arizona’s insanity test and
its Mott rule each violate due process. As to the insanity
standard, Clark claimed (as he had argued earlier) that the
Arizona Legislature had impermissibly narrowed its stand
ard in 1993 when it eliminated the first part of the two-part
insanity test announced in M’Naghten’s Case, 10 Cl. & Fin.
200, 8 Eng. Rep. 718 (1843). The court denied the motion.
The Court of Appeals of Arizona affirmed Clark’s convic
tion, treating the conclusion on sanity as supported by
enough evidence to withstand review for abuse of discretion,
and holding the State’s insanity scheme consistent with due
process. App. 336. As to the latter, the Court of Appeals
reasoned that there is no constitutional requirement to rec
ognize an insanity defense at all, the bounds of which are left
to the State’s discretion. Beyond that, the appellate court
followed Mott, reading it as barring the trial court’s consid
4 Clark did not at this time make an additional offer of proof, as contem
plated by the trial court when it ruled that it would consider evidence
bearing on insanity as to insanity but not as to mens rea. See n. 3, supra.

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eration of evidence of Clark’s mental illness and capacity di
rectly on the element of mens rea. The Supreme Court of
Arizona denied further review.
We granted certiorari to decide whether due process pro
hibits Arizona from thus narrowing its insanity test or from
excluding evidence of mental illness and incapacity due to
mental illness to rebut evidence of the requisite criminal in
tent. 546 U. S. 1060 (2005). We now affirm.
II
Clark first says that Arizona’s definition of insanity, being
only a fragment of the Victorian standard from which it de
rives, violates due process. The landmark English rule in
M’Naghten’s Case, supra, states that
“the jurors ought to be told . . . that to establish a de
fence on the ground of insanity, it must be clearly proved
that, at the time of the committing of the act, the party
accused was laboring under such a defect of reason, from
disease of the mind, as not to know the nature and qual
ity of the act he was doing; or, if he did know it, that he
did not know he was doing what was wrong.” Id., at
210, 8 Eng. Rep., at 722.
The first part asks about cognitive capacity: whether a men
tal defect leaves a defendant unable to understand what he
is doing. The second part presents an ostensibly alternative
basis for recognizing a defense of insanity understood as a
lack of moral capacity: whether a mental disease or defect
leaves a defendant unable to understand that his action is
wrong.
When the Arizona Legislature first codified an insanity
rule, it adopted the full M’Naghten statement (subject to
modifications in details that do not matter here):
“A person is not responsible for criminal conduct if at
the time of such conduct the person was suffering from
such a mental disease or defect as not to know the na

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ture and quality of the act or, if such person did know,
that such person did not know that what he was doing
was wrong.” Ariz. Rev. Stat. Ann. § 13–502 (West
1978).5
In 1993, the legislature dropped the cognitive incapacity
part, leaving only moral incapacity as the nub of the stated
definition. See 1993 Ariz. Sess. Laws ch. 256, §§ 2–3.6
Under current Arizona law, a defendant will not be adjudged
insane unless he demonstrates that “at the time of the com
mission of the criminal act [he] was afflicted with a mental
disease or defect of such severity that [he] did not know the
criminal act was wrong,” Ariz. Rev. Stat. Ann. § 13–502(A)
(West 2001).
A
Clark challenges the 1993 amendment excising the express
reference to the cognitive incapacity element. He insists
that the side-by-side M’Naghten test represents the mini
mum that a government must provide in recognizing an
alternative to criminal responsibility on grounds of mental
illness or defect, and he argues that elimination of the
M’Naghten reference to nature and quality “ ‘offends [a] prin
ciple of justice so rooted in the traditions and conscience of
our people as to be ranked as fundamental,’ ” Patterson v.
5 This statutory standard followed the Arizona Supreme Court’s declara
tion that Arizona has “uniformly adhered” to the two-part M’Naghten
standard. State v. Schantz, 98 Ariz. 200, 206, 403 P. 2d 521, 525 (1965)
(citing cases), cert. denied, 382 U. S. 1015 (1966).
6 This change was accompanied by others, principally an enumeration of
mental states excluded from the category of “mental disease or defect,”
such as voluntary intoxication and other conditions, and a change of the
insanity verdict from “not responsible for criminal conduct” by reason of
insanity to “guilty except insane.” See 1993 Ariz. Sess. Laws ch. 256,
§§ 2–3. The 1993 amendments were prompted, at least in part, by an
acquittal by reason of insanity in a murder case. See Note, Arizona’s
Insane Response to Insanity, 40 Ariz. L. Rev. 287, 290 (1998).

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New York, 432 U. S. 197, 202 (1977) (quoting Speiser v. Ran
dall, 357 U. S. 513, 523 (1958)); see also Leland v. Oregon,
343 U. S. 790, 798 (1952).
The claim entails no light burden, see Montana v. Egel
hoff, 518 U. S. 37, 43 (1996) (plurality opinion), and Clark does
not carry it. History shows no deference to M’Naghten that
could elevate its formula to the level of fundamental princi
ple, so as to limit the traditional recognition of a State’s ca
pacity to define crimes and defenses, see Patterson, supra,
at 210; see also Foucha v. Louisiana, 504 U. S. 71, 96 (1992)
(Kennedy, J., dissenting).
Even a cursory examination of the traditional Anglo-
American approaches to insanity reveals significant differ
ences among them, with four traditional strains variously
combined to yield a diversity of American standards. The
main variants are the cognitive incapacity, the moral incapac
ity, the volitional incapacity, and the product-of-mental
illness tests.7 The first two emanate from the alternatives
stated in the M’Naghten rule. The volitional incapacity or
irresistible-impulse test, which surfaced over two centuries
ago (first in England,8 then in this country 9), asks whether a
person was so lacking in volition due to a mental defect or
illness that he could not have controlled his actions. And
the product-of-mental-illness test was used as early as
1870,10 and simply asks whether a person’s action was a prod
7 “Capacity” is understood to mean the ability to form a certain state of
mind or motive, understand or evaluate one’s actions, or control them.
8 See Queen v. Oxford, 9 Car. & P. 525, 546, 173 Eng. Rep. 941, 950 (1840)
(“If some controlling disease was, in truth, the acting power within [the
defendant] which he could not resist, then he will not be responsible”);
Hadfield’s Case, 27 How. St. Tr. 1281, 1314–1315, 1354–1355 (K. B. 1800).
But cf. Queen v. Burton, 3 F. & F. 772, 780, 176 Eng. Rep. 354, 357 (1863)
(rejecting the irresistible-impulse test as “a most dangerous doctrine”).
9 E. g., Parsons v. State, 81 Ala. 577, 2 So. 854 (1887); State v. Thompson,
Wright’s Ohio Rep. 617 (1834).
10 State v. Jones, 50 N. H. 369 (1871); State v. Pike, 49 N. H. 399 (1870).

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uct of a mental disease or defect.11 Seventeen States and
the Federal Government have adopted a recognizable ver
sion of the M’Naghten test with both its cognitive incapacity
and moral incapacity components.12 One State has adopted
11 This distillation of the Anglo-American insanity standards into combi
nations of four building blocks should not be read to signify that no other
components contribute to these insanity standards or that there are no
material distinctions between jurisdictions testing insanity with the same
building blocks. For example, the jurisdictions limit, in varying degrees,
which sorts of mental illness or defect can give rise to a successful insanity
defense. Compare, e. g., Ariz. Rev. Stat. Ann. § 13–502(A) (West 2001)
(excluding from definition of “mental disease or defect” acute voluntary
intoxication, withdrawal from alcohol or drugs, character defects, psycho
sexual disorders, and impulse control disorders) with, e. g., Ind. Code § 35–
41–3–6(b) (West 2004) (excluding from definition of “mental disease or
defect” “abnormality manifested only by repeated unlawful or antisocial
conduct”). We need not compare the standards under a finer lens because
our coarser analysis shows that the standards vary significantly.
12 See 18 U. S. C. § 17; Ala. Code § 13A–3–1 (1994); Cal. Penal Code Ann.
§ 25 (West 1999); Colo. Rev. Stat. Ann. § 16–8–101.5 (2005); Fla. Stat.
§ 775.027 (2003); Iowa Code § 701.4 (2005); Minn. Stat. § 611.026 (2004); Ste
vens v. State, 806 So. 2d 1031, 1050–1051 (Miss. 2001); Mo. Rev. Stat.
§ 562.086 (2000); State v. Harms, 263 Neb. 814, 836–837, 643 N. W. 2d 359,
378–379 (2002); Nev. Rev. Stat. § 194.010 (2004); Finger v. State, 117 Nev.
548, 553–577, 27 P. 3d 66, 70–85 (2001); N. J. Stat. Ann. § 2C:4–1 (West
2005); N. Y. Penal Law Ann. § 40.15 (West 2004); State v. Thompson, 328
N. C. 477, 485–486, 402 S. E. 2d 386, 390 (1991); Burrows v. State, 640 P. 2d
533, 540–541 (Okla. Crim. App. 1982) (interpreting statutory language ex
cusing from criminal responsibility mentally ill defendants when “at the
time of committing the act charged against them they were incapable of
knowing its wrongfulness,” Okla. Stat., Tit. 21, § 152(4) (West 2001), to
mean the two-part M’Naghten test); 18 Pa. Cons. Stat. § 315 (2002); Tenn.
Code Ann. § 39–11–501 (2003); Wash. Rev. Code § 9A.12.010 (2004). North
Dakota has a unique test, which appears to be a modified version of
M’Naghten, asking whether a defendant “lacks substantial capacity to
comprehend the harmful nature or consequences of the conduct, or the
conduct is the result of a loss or serious distortion of the individual’s capac
ity to recognize reality,” N. D. Cent. Code Ann. § 12.1–04.1–01(1)(a) (Lexis
1997), when “[i]t is an essential element of the crime charged that the
individual act willfully,” § 12.1–04.1–01(1)(b).

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only M’Naghten’s cognitive incapacity test,13 and 10 (includ
ing Arizona) have adopted the moral incapacity test alone.14
Fourteen jurisdictions, inspired by the Model Penal Code,15
have in place an amalgam of the volitional incapacity test
and some variant of the moral incapacity test, satisfaction of
either (generally by showing a defendant’s substantial lack
of capacity) being enough to excuse.16 Three States combine
a full M’Naghten test with a volitional incapacity for
mula.17 And New Hampshire alone stands by the product
of-mental-illness test.18 The alternatives are multiplied
further by variations in the prescribed insanity verdict: a
significant number of these jurisdictions supplement the
traditional “not guilty by reason of insanity” verdict with an
13 Alaska Stat. § 12.47.010 (2004).
14 Ariz. Rev. Stat. Ann. § 13–502 (West 2001); Del. Code Ann., Tit. 11,
§ 401 (1995); Ind. Code § 35–41–3–6 (West 2004); Ill. Comp. Stat., ch. 720,
§ 5/6–2 (West 2004); La. Stat. Ann. § 14:14 (West 1997); Me. Rev. Stat. Ann.,
Tit. 17–A, § 39 (2006); Ohio Rev. Code Ann. § 2901.01(A)(14) (Lexis 2006);
S. C. Code Ann. § 17–24–10 (2003); S. D. Codified Laws § 22–1–2(20) (2005
Supp. Pamphlet); Tex. Penal Code Ann. § 8.01 (West 2003).
15 ALI, Model Penal Code § 4.01(1), p. 66 (Proposed Official Draft 1962)
(“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”).
16 Ark. Code Ann. § 5–2–312 (2006); Conn. Gen. Stat. § 53a–13 (2005);
Malede v. United States, 767 A. 2d 267, 269 (D. C. 2001); Ga. Code Ann.
§§ 16–3–2, 16–3–3 (2003); Haw. Rev. Stat. § 704–400 (1993); Ky. Rev. Stat.
Ann. § 504.020 (West 2003); Md. Crim. Proc. Code Ann. § 3–109 (Lexis
2001); Commonwealth v. McLaughlin, 431 Mass. 506, 508, 729 N. E. 2d
252, 255 (2000); Ore. Rev. Stat. § 161.295 (2003); State v. Martinez, 651
A. 2d 1189, 1193 (R. I. 1994); Vt. Stat. Ann., Tit. 13, § 4801 (1998); State v.
Lockhart, 208 W. Va. 622, 630, 542 S. E. 2d 443, 451 (2000); Wis. Stat.
§ 971.15 (2003–2004); Wyo. Stat. Ann. § 7–11–304 (2005).
17 Mich. Comp. Laws Ann. § 768.21a (West 2000); State v. Hartley, 90
N. M. 488, 490–491, 565 P. 2d 658, 660–661 (1977); Bennett v. Common
wealth, 29 Va. App. 261, 277, 511 S. E. 2d 439, 446–447 (1999).
18 State v. Plante, 134 N. H. 456, 461, 594 A. 2d 1279, 1283 (1991).

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alternative of “guilty but mentally ill.” 19 Finally, four
States have no affirmative insanity defense,20 though one
provides for a “guilty and mentally ill” verdict.21 These
four, like a number of others that recognize an affirmative
insanity defense, allow consideration of evidence of mental
illness directly on the element of mens rea defining the
offense.22
With this varied background, it is clear that no particular
formulation has evolved into a baseline for due process, and
that the insanity rule, like the conceptualization of criminal
offenses, is substantially open to state choice. Indeed, the
legitimacy of such choice is the more obvious when one con
siders the interplay of legal concepts of mental illness or de
ficiency required for an insanity defense, with the medical
concepts of mental abnormality that influence the expert
opinion testimony by psychologists and psychiatrists com
monly introduced to support or contest insanity claims. For
medical definitions devised to justify treatment, like legal
ones devised to excuse from conventional criminal responsi
bility, are subject to flux and disagreement. See infra, at
19 See, e. g., Alaska Stat. §§ 12.47.020(c), 12.47.030 (2004); Del. Code Ann.,
Tit. 11, § 401 (1995); Ga. Code Ann. § 17–7–131 (2004); Ill. Comp. Stat.,
ch. 720, § 5/6–2 (West 2004); Ind. Code §§ 35–35–2–1, 35–36–1–1, 35–36–2–3
(West 2004); Ky. Rev. Stat. Ann. § 504.130 (West 2003); Mich. Comp. Laws
Ann. § 768.36 (West Supp. 2006); N. M. Stat. Ann. § 31–9–3 (2000); 18 Pa.
Cons. Stat. § 314 (2002); S. C. Code Ann. § 17–24–20 (2003); S. D. Codified
Laws § 23A–26–14 (2004). Usually, a defendant found “guilty but men
tally ill” will receive mental-health treatment until his mental health has
rebounded, at which point he must serve the remainder of his imposed
sentence. See, e. g., Alaska Stat. § 12.47.050 (2004).
20 Idaho Code § 18–207 (Lexis 2004); Kan. Stat. Ann. § 22–3220 (1995);
Mont. Code Ann. §§ 46–14–102, 46–14–311 (2005); Utah Code Ann. § 76–2–
305 (Lexis 2003). We have never held that the Constitution mandates an
insanity defense, nor have we held that the Constitution does not so re
quire. This case does not call upon us to decide the matter.
21 §§ 77–16a–101, 77–16a–103, 77–16a–104 (Lexis 2003).
22 See statutes cited in n. 20, supra.

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774–775; cf. Leland, 343 U. S., at 800–801 (no due process
violation for adopting the M’Naghten standard rather than
the irresistible-impulse test because scientific knowledge
does not require otherwise and choice of test is a matter
of policy). There being such fodder for reasonable debate
about what the cognate legal and medical tests should be,
due process imposes no single canonical formulation of legal
insanity.
B
Nor does Arizona’s abbreviation of the M’Naghten state
ment raise a proper claim that some constitutional minimum
has been shortchanged. Clark’s argument of course as
sumes that Arizona’s former statement of the M’Naghten
rule, with its express alternative of cognitive incapacity, was
constitutionally adequate (as we agree). That being so, the
abbreviated rule is no less so, for cognitive incapacity is rele
vant under that statement, just as it was under the more
extended formulation, and evidence going to cognitive inca
pacity has the same significance under the short form as it
had under the long.
Though Clark is correct that the application of the moral
incapacity test (telling right from wrong) does not necessar
ily require evaluation of a defendant’s cognitive capacity to
appreciate the nature and quality of the acts charged against
him, see Brief for Petitioner 46–47, his argument fails to
recognize that cognitive incapacity is itself enough to dem
onstrate moral incapacity. Cognitive incapacity, in other
words, is a sufficient condition for establishing a defense of
insanity, albeit not a necessary one. As a defendant can
therefore make out moral incapacity by demonstrating cogni
tive incapacity, evidence bearing on whether the defendant
knew the nature and quality of his actions is both relevant
and admissible. In practical terms, if a defendant did not
know what he was doing when he acted, he could not have
known that he was performing the wrongful act charged as

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a crime.23 Indeed, when the two-part rule was still in effect,
the Supreme Court of Arizona held that a jury instruction
on insanity containing the moral incapacity part but not a
full recitation of the cognitive incapacity part was fine, as
the cognitive incapacity part might be “ ‘treated as adding
nothing to the requirement that the accused know his act
was wrong.’ ” State v. Chavez, 143 Ariz. 238, 239, 693 P. 2d
893, 894 (1984) (quoting A. Goldstein, The Insanity Defense
50 (1967)).
The Court of Appeals of Arizona acknowledged as much
in this case, too, see App. 350 (“It is difficult to imagine that
a defendant who did not appreciate the ‘nature and quality’
of the act he committed would reasonably be able to perceive
that the act was ‘wrong’ ”), and thus aligned itself with the
long-accepted understanding that the cognitively incapaci
tated are a subset of the morally incapacitated within the
meaning of the standard M’Naghten rule, see, e. g., Goldstein,
supra, at 51 (“In those situations where the accused does not
know the nature and quality of his act, in the broad sense, he
will not know that it was wrong, no matter what construction
‘wrong’ is given”); 1 W. LaFave, Substantive Criminal Law
§ 7.2(b)(3), p. 536 (2d ed. 2003) (“Many courts feel that knowl
edge of ‘the nature and quality of the act’ is the mere equiva
lent of the ability to know that the act was wrong” (citing
cases)); id., § 7.2(b)(4), at 537 (“If the defendant does not
know the nature and quality of his act, then quite obviously
he does not know that his act is ‘wrong,’ and this is true
without regard to the interpretation given to the word
23 He might, of course, have thought delusively he was doing something
just as wrongful as the act charged against him, but this is not the test:
he must have understood that he was committing the act charged and that
it was wrongful, see Ariz. Rev. Stat. Ann. § 13–502(A) (West 2001)
(“A person may be found guilty except insane if at the time of the commis
sion of the criminal act the person was afflicted with a mental disease
or defect of such severity that the person did not know the criminal act
was wrong”).

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‘wrong’ ”); cf. 1 R. Gerber, Criminal Law of Arizona 502–7,
n. 1 (2d ed. 1993).24
Clark, indeed, adopted this very analysis himself in the
trial court: “[I]f [Clark] did not know he was shooting at a
police officer, or believed he had to shoot or be shot, even
though his belief was not based in reality, this would estab
lish that he did not know what he was doing was wrong.”
Record, Doc. 374, at 1. The trial court apparently agreed,
for the judge admitted Clark’s evidence of cognitive incapac
ity for consideration under the State’s moral incapacity for
mulation. And Clark can point to no evidence bearing on
24 We think this logic holds true in the face of the usual rule of statutory
construction of “ ‘ “giv[ing] effect, if possible, to every clause and word of
a statute,” ’ ” Duncan v. Walker, 533 U. S. 167, 174 (2001) (quoting United
States v. Menasche, 348 U. S. 528, 538–539 (1955)); see also 2 J. Sutherland,
Statutes and Statutory Construction § 4705 (3d ed. 1943). Insanity stand
ards are formulated to guide the factfinder to determine the blameworthi
ness of a mentally ill defendant. See, e. g., Jones v. United States, 463
U. S. 354, 373, n. 4 (1983) (Brennan, J., dissenting). The M’Naghten test
is a sequential test, first asking the factfinder to conduct the easier enquiry
whether a defendant knew the nature and quality of his actions. If not,
the defendant is to be considered insane and there is no need to pass to
the harder and broader enquiry whether the defendant knew his actions
were wrong. And, because, owing to this sequence, the factfinder is to
ask whether a defendant lacks moral capacity only when he possesses cog
nitive capacity, the only defendants who will be found to lack moral capac
ity are those possessing cognitive capacity. Cf. 2 C. Torcia, Wharton’s
Criminal Law § 101 (15th ed. 1994). Though, before 1993, Arizona had in
place the full M’Naghten test with this sequential enquiry, see, e. g.,
Schantz, 98 Ariz., at 207, 403 P. 2d, at 525, it would appear that the legisla
ture eliminated the cognitive capacity part not to change the meaning of
the insanity standard but to implement its judgment that a streamlined
standard with only the moral capacity part would be easier for the jury to
apply, see Arizona House of Representatives, Judiciary Committee Notes
3 (Mar. 18, 1993); 1 R. Gerber, Criminal Law of Arizona 502–6, 502–11 (2d
ed. 1993 and Supp. 2000). This is corroborated by the State’s choice for
many years against revising the applicable recommended jury instruc
tion (enumerating the complete M’Naghten test) in order to match the
amended statutory standard. See 1 Gerber, supra, at 502–6 (2d ed. 1993
and Supp. 2000).

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insanity that was excluded. His psychiatric expert and a
number of lay witnesses testified to his delusions, and this
evidence tended to support a description of Clark as lacking
the capacity to understand that the police officer was a
human being. There is no doubt that the trial judge consid
ered the evidence as going to an issue of cognitive capacity,
for in finding insanity not proven he said that Clark’s men
tal illness “did not . . . distort his perception of reality so
severely that he did not know his actions were wrong,”
App. 334.
We are satisfied that neither in theory nor in practice did
Arizona’s 1993 abridgment of the insanity formulation de
prive Clark of due process.
III
Clark’s second claim of a due process violation challenges
the rule adopted by the Supreme Court of Arizona in State
v. Mott, 187 Ariz. 536, 931 P. 2d 1046, cert. denied, 520 U. S.
1234 (1997). This case ruled on the admissibility of testi
mony from a psychologist offered to show that the defendant
suffered from battered women’s syndrome and therefore
lacked the capacity to form the mens rea of the crime
charged against her. The opinion variously referred to the
testimony in issue as “psychological testimony,” 187 Ariz.,
at 541, 931 P. 2d, at 1051, and “expert testimony,” ibid., and
implicitly equated it with “expert psychiatric evidence,”
id., at 540, 931 P. 2d, at 1050 (internal quotation marks omit
ted), and “psychiatric testimony,” id., at 541, 931 P. 2d, at
1051.25 The state court held that testimony of a professional
psychologist or psychiatrist about a defendant’s mental inca
pacity owing to mental disease or defect was admissible, and
could be considered, only for its bearing on an insanity de
fense; such evidence could not be considered on the element
25 We thus think the dissent reads Mott too broadly. See post, at 786
(opinion of Kennedy, J.) (no distinction between observation and mental
disease testimony, see infra, at 757–758, or lay and expert).

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of mens rea, that is, what the State must show about a de
fendant’s mental state (such as intent or understanding)
when he performed the act charged against him. See id., at
541, 544, 931 P. 2d, at 1051, 1054.26
A
Understanding Clark’s claim requires attention to the cat
egories of evidence with a potential bearing on mens rea.
First, there is “observation evidence” in the everyday sense,
testimony from those who observed what Clark did and
heard what he said; this category would also include testi
mony that an expert witness might give about Clark’s tend
ency to think in a certain way and his behavioral characteris
tics. This evidence may support a professional diagnosis of
mental disease and in any event is the kind of evidence that
can be relevant to show what in fact was on Clark’s mind
when he fired the gun. Observation evidence in the record
covers Clark’s behavior at home and with friends, his expres
sions of belief around the time of the killing that “aliens”
were inhabiting the bodies of local people (including govern
ment agents),27 his driving around the neighborhood before
the police arrived, and so on. Contrary to the dissent’s char
acterization, see post, at 782 (opinion of Kennedy, J.), obser
26 The more natural reading of Mott suggests to us that this evidence
cannot be considered as to mens rea even if the defendant establishes his
insanity, though one might read Mott otherwise.
27 Clark’s parents testified that, in the months before the shooting and
even days beforehand, Clark called them “aliens” and thought that “aliens”
were out to get him. See, e. g., Tr. of Bench Trial in No. CR 2000–538,
pp. 110–112, 136, 226–228 (Aug. 20, 2003). One night before the shooting,
according to Clark’s mother, Clark repeatedly viewed a popular film char
acterized by her as telling a story about “aliens” masquerading as govern
ment agents, a story Clark insisted was real despite his mother’s protesta
tions to the contrary. See id., at 59–60 (Aug. 21, 2003). And two months
after the shooting, Clark purportedly told his parents that his hometown,
Flagstaff, was inhabited principally by “aliens,” who had to be stopped,
and that the only way to stop them was with bullets. See, e. g., id., at
131–132 (Aug. 20, 2003); id., at 24–25 (Aug. 21, 2003).

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vation evidence can be presented by either lay or expert
witnesses.
Second, there is “mental-disease evidence” in the form of
opinion testimony that Clark suffered from a mental disease
with features described by the witness. As was true here,
this evidence characteristically but not always 28 comes from
professional psychologists or psychiatrists who testify as ex
pert witnesses and base their opinions in part on examina
tion of a defendant, usually conducted after the events in
question. The thrust of this evidence was that, based on
factual reports, professional observations, and tests, Clark
was psychotic at the time in question, with a condition that
fell within the category of schizophrenia.
Third, there is evidence we will refer to as “capacity evi
dence” about a defendant’s capacity for cognition and moral
judgment (and ultimately also his capacity to form mens
rea). This, too, is opinion evidence. Here, as it usually
does,29 this testimony came from the same experts and con
centrated on those specific details of the mental condition
that make the difference between sanity and insanity under
the Arizona definition.30 In their respective testimony on
28 This is contrary to the dissent’s understanding. See post, at 782–783
(opinion of Kennedy, J.).
29 In conflict with the dissent’s characterization, see post, at 782 (opinion
of Kennedy, J.), it does not always, however, come from experts.
30 Arizona permits capacity evidence, see, e. g., State v. Sanchez, 117
Ariz. 369, 373, 573 P. 2d 60, 64 (1977); see also Ariz. Rule Evid. 704 (2006)
(allowing otherwise admissible evidence on testimony “embrac[ing] an ul
timate issue to be decided by the trier of fact”), though not every jurisdic
tion permits such evidence on the ultimate issue of insanity. See, e. g.,
Fed. Rule Evid. 704(b) (“No expert witness testifying with respect to the
mental state or condition of a defendant in a criminal case may state an
opinion or inference as to whether the defendant did or did not have the
mental state or condition constituting an element of the crime charged or
of a defense thereto. Such ultimate issues are matters for the trier of
fact alone”); United States v. Dixon, 185 F. 3d 393, 400 (CA5 1999) (in the

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these details the experts disagreed: the defense expert gave
his opinion that the symptoms or effects of the disease in
Clark’s case included inability to appreciate the nature of
his action and to tell that it was wrong, whereas the State’s
psychiatrist was of the view that Clark was a schizophrenic
who was still sufficiently able to appreciate the reality of
shooting the officer and to know that it was wrong to do
that.31
A caveat about these categories is in order. They attempt
to identify different kinds of testimony offered in this case
in terms of explicit and implicit distinctions made in Mott.
What we can say about these categories goes to their cores,
however, not their margins. Exact limits have thus not
been worked out in any Arizona law that has come to our
attention, and in this case, neither the courts in their rulings
nor counsel in objections invoked or required precision in
applying the Mott rule’s evidentiary treatment, as we ex
plain below. Necessarily, then, our own decision can address
only core issues, leaving for other cases any due process
claims that may be raised about the treatment of evidence
whose categorization is subject to dispute.
face of mental-disease evidence, Rule 704(b) prohibits an expert “from
testifying that [the mental-disease evidence] does or does not prevent the
defendant from appreciating the wrongfulness of his actions”).
31 Arizona permits evidence bearing on insanity to be presented by
either lay or expert witnesses. See State v. Bay, 150 Ariz. 112, 116, 722
P. 2d 280, 284 (1986). According to Bay, “[f]oundationally, a lay witness
must have had an opportunity to observe the past conduct and history of
a defendant; the fact that he is a lay witness goes not to the admissibility
of the testimony but rather to its weight.” Ibid. (citation omitted); see
also State v. Hughes, 193 Ariz. 72, 83, 969 P. 2d 1184, 1195 (1998). In fact,
a defendant can theoretically establish insanity solely via lay testimony.
See Bay, supra, at 116, 722 P. 2d, at 284. But cf. State v. McMurtrey, 136
Ariz. 93, 100, 664 P. 2d 637, 644 (1983) (“[I]t is difficult to imagine how a
defendant could place his or her sanity in issue . . . without expert testi
mony as to the defendant’s state of mind at the time of the crime”).

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B
It is clear that Mott itself imposed no restriction on consid
ering evidence of the first sort, the observation evidence.
We read the Mott restriction to apply, rather, to evidence
addressing the two issues in testimony that characteristi
cally comes only from psychologists or psychiatrists qualified
to give opinions as expert witnesses: mental-disease evi
dence (whether at the time of the crime a defendant suffered
from a mental disease or defect, such as schizophrenia) and
capacity evidence (whether the disease or defect left him in
capable of performing or experiencing a mental process de
fined as necessary for sanity such as appreciating the nature
and quality of his act and knowing that it was wrong).
Mott was careful to distinguish this kind of opinion evi
dence from observation evidence generally and even from
observation evidence that an expert witness might offer,
such as descriptions of a defendant’s tendency to think in a
certain way or his behavioral characteristics; the Arizona
court made it clear that this sort of testimony was perfectly
admissible to rebut the prosecution’s evidence of mens rea,
187 Ariz., at 544, 931 P. 2d, at 1054. Thus, only opinion testi
mony going to mental defect or disease, and its effect on the
cognitive or moral capacities on which sanity depends under
the Arizona rule, is restricted.
In this case, the trial court seems to have applied the Mott
restriction to all evidence offered by Clark for the purpose
of showing what he called his inability to form the required
mens rea, see, e. g., Record, Doc. 406, at 7–10 (that is, an
intent to kill a police officer on duty, or an understanding
that he was engaging in the act of killing such an officer,
see Ariz. Rev. Stat. Ann. § 13–1105(A)(3) (West Supp. 2005)).
Thus, the trial court’s restriction may have covered not only
mental-disease and capacity evidence as just defined, but also
observation evidence offered by lay (and expert) witnesses
who described Clark’s unusual behavior. Clark’s objection
to the application of the Mott rule does not, however, turn

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on the distinction between lay and expert witnesses or the
kinds of testimony they were competent to present.32
C
There is some, albeit limited, disagreement between the
dissent and ourselves about the scope of the claim of error
properly before us. To start with matters of agreement, all
Members of the Court agree that Clark’s general attack on
the Mott rule covers its application in confining consideration
of capacity evidence to the insanity defense.
In practical terms, our agreement on issues presented ex
tends to a second point. Justice Kennedy understands
that Clark raised an objection to confining mental-disease
evidence to the insanity issue. As he sees it, Clark in effect
claimed that in dealing with the issue of mens rea the trial
judge should have considered expert testimony on what may
characteristically go through the mind of a schizophrenic,
when the judge considered what in fact was in Clark’s mind
at the time of the shooting. See post, at 783 (dissenting
opinion) (“[T]he opinion that Clark had paranoid schizophre
nia—an opinion shared by experts for both the prosecution
and defense—bears on efforts to determine, as a factual mat
ter, whether he knew he was killing a police officer”). He
thus understands that defense counsel claimed a right to
rebut the State’s mens rea demonstration with testimony
about how schizophrenics may hallucinate voices and other
sounds, about their characteristic failure to distinguish the
content of their imagination from what most people perceive
as exterior reality, and so on. It is important to be clear
that this supposed objection was not about dealing with tes
32 With respect to “the limited factual issues the trial court held it could
consider under [Ariz. Rev. Stat. Ann.] § 13–502 and Mott, defense counsel
made no additional ‘offer of proof ’ at the conclusion of the case but pre
served [Clark’s] legal contentions by asking the court to consider all of the
evidence presented in determining whether the state had proved its case.”
Brief for Petitioner 10, n. 20 (citation omitted).

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timony based on observation of Clark showing that he had
auditory hallucinations when he was driving around, or failed
in fact to appreciate objective reality when he shot; this ob
jection went to use of testimony about schizophrenics, not
about Clark in particular. While we might dispute how
clearly Clark raised this objection, we have no doubt that
the objection falls within a general challenge to the Mott
rule; we understand that Mott is meant to confine to the
insanity defense any consideration of characteristic behavior
associated with mental disease, see 187 Ariz., at 544, 931
P. 2d, at 1054 (contrasting State v. Christensen, 129 Ariz. 32,
628 P. 2d 580 (1981), and State v. Gonzales, 140 Ariz. 349, 681
P. 2d 1368 (1984)). We will therefore assume for argument
that Clark raised this claim, as we consider the due process
challenge to the Mott rule.
The point on which we disagree with the dissent, however,
is this: did Clark apprise the Arizona courts that he believed
the trial judge had erroneously limited the consideration
of observation evidence, whether from lay witnesses like
Clark’s mother or (possibly) the expert witnesses who ob
served him? This sort of evidence was not covered by the
Mott restriction, and confining it to the insanity issue would
have been an erroneous application of Mott as a matter of
Arizona law. For the following reasons we think no such
objection was made in a way the Arizona courts could have
understood it, and that no such issue is before us now. We
think the only issue properly before us is the challenge to
Mott on due process grounds, comprising objections to limits
on the use of mental-disease and capacity evidence.
It is clear that the trial judge intended to apply Mott:
“[R]ecognizing that much of the evidence that [the de
fense is] going to be submitting, in fact all of it, as far
as I know . . . that has to do with the insanity could also
arguably be made along the lines of the Mott issues as
to form and intent and his capacity for the intent. I’m
going to let you go ahead and get all that stuff in because

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it goes to the insanity issue and because we’re not in
front of a jury. At the end, I’ll let you make an offer of
proof as to the intent, the Mott issues, but I still think
the supreme court decision is the law of the land in this
state.” App. 9.
At no point did the trial judge specify any particular evi
dence that he refused to consider on the mens rea issue.
Nor did defense counsel specify any observation or other par
ticular evidence that he claimed was admissible but wrongly
excluded on the issue of mens rea, so as to produce a clearer
ruling on what evidence was being restricted on the author
ity of Mott and what was not. He made no “offer of proof ”
in the trial court; 33 and although his brief in the Arizona
Court of Appeals stated at one point that it was not incon
sistent with Mott to consider nonexpert evidence indicating
mental illness on the issue of mens rea, and argued that the
trial judge had failed to do so, Appellant’s Opening Brief in
No. 1CA–CR–03–0851 etc., pp. 48–49 (hereinafter Appel
lant’s Opening Brief), he was no more specific than that, see,
e. g., id., at 52 (“The Court’s ruling in Mott and the trial
court’s refusal to consider whether as a result of suffering
from paranoid schizophrenia [Clark] could not formulate the
mens rea necessary for first degree murder violated his right
to due process”). Similarly, we read the Arizona Court of
Appeals to have done nothing more than rely on Mott to
reject the claim that due process forbids restricting evidence
bearing on “[a]bility to [f]orm [m]ens [r]ea,” App. 351 (em
33 We do not agree with the State’s argument that the failure to make
an offer of proof, see n. 4, supra, is a bar to pressing Clark’s claim about
the admissibility of mental-illness or capacity evidence as to mens rea, see
Brief for Respondent 27–29, especially when the Arizona Court of Appeals
rejected Clark’s argument on the merits rather than clearly on this
ground, see App. 351–353; see also Michigan v. Long, 463 U. S. 1032, 1042
(1983) (“[I]t is not clear from the opinion itself that the state court relied
upon an adequate and independent state ground and . . . it fairly appears
that the state court rested its decision primarily on federal law”).

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phasis in original), (i. e., mental-disease and capacity evi
dence) to the insanity determination. See id., at 351–353.
This failure in the state courts to raise any clear claim
about observation evidence, see Appellant’s Opening Brief
46–52, is reflected in the material addressed to us, see Brief
for Petitioner 13–32. In this Court both the question pre
sented and the following statement of his position were
couched in similarly worded general terms:
“I. ERIC WAS DENIED DUE PROCESS WHEN
THE TRIAL COURT REFUSED TO CONSIDER EV-
IDENCE OF HIS SEVERE MENTAL ILLNESS IN
DETERMINING FACTUALLY WHETHER THE
PROSECUTION PROVED THE MENTAL ELE-
MENTS OF THE CRIME CHARGED.” Id., at 13.
But as his counsel made certain beyond doubt in his reply
brief,
“Eric’s Point I is and always has been an attack on the
rule of State v. Mott, which both courts below held appli
cable and binding. Mott announced a categorical ‘rejec
tion of the use of psychological testimony to challenge
the mens rea element of a crime,’ and upheld this rule
against federal due process challenge.” Reply Brief for
Petitioner 2 (citations omitted).
This explanation is supported by other statements in Clark’s
briefs in both the State Court of Appeals and this Court,
replete with the consistently maintained claim that it was
error to limit evidence of mental illness and incapacity to its
bearing on the insanity defense, excluding it from consider
ation on the element of mens rea. See, e. g., Appellant’s
Opening Brief 46, 47, 51; Brief for Petitioner 11, 13, 16, 20–23.
In sum, the trial court’s ruling, with its uncertain edges,
may have restricted observation evidence admissible on
mens rea to the insanity defense alone, but we cannot be

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sure.34 But because a due process challenge to such a re
striction of observation evidence was, by our measure, nei
ther pressed nor passed upon in the Arizona Court of Ap
peals, we do not consider it. See, e. g., Kentucky v. Stincer,
482 U. S. 730, 747, n. 22 (1987); Illinois v. Gates, 462 U. S.
213, 217–224 (1983). What we do know, and now consider, is
Clark’s claim that Mott denied due process because it “pre
clude[d] Eric from contending that . . . factual inferences”
of the “mental states which were necessary elements of the
crime charged” “should not be drawn because the behavior
was explainable, instead, as a manifestation of his chronic
paranoid schizophrenia.” Brief for Petitioner 13 (emphasis
in original). We consider the claim, as Clark otherwise puts
it, that “Arizona’s prohibition of ‘diminished capacity’ evi
dence by criminal defendants violates” due process, ibid.
D
Clark’s argument that the Mott rule violates the Four
teenth Amendment guarantee of due process turns on the
application of the presumption of innocence in criminal cases,
the presumption of sanity, and the principle that a criminal
defendant is entitled to present relevant and favorable evi
dence on an element of the offense charged against him.
34 We therefore have no reason to believe that the courts of Arizona
would have failed to restrict their application of Mott to the professional
testimony the Mott opinion was stated to cover, if Clark’s counsel had
specified any observation evidence he claimed to be generally admissible
and relevant to mens rea. Nothing that we hold here is authority for
restricting a factfinder’s consideration of observation evidence indicating
state of mind at the time of a criminal offense (conventional mens rea
evidence) as distinct from professional mental-disease or capacity evidence
going to ability to form a certain state of mind during a period that in
cludes the time of the offense charged. And, of course, nothing held here
prevents Clark from raising this discrete claim when the case returns to
the courts of Arizona, if consistent with the State’s procedural rules.

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1
The first presumption is that a defendant is innocent un
less and until the government proves beyond a reasonable
doubt each element of the offense charged, see Patterson,
432 U. S., at 210–211; In re Winship, 397 U. S. 358, 361–364
(1970), including the mental element or mens rea. Before
the last century, the mens rea required to be proven for par
ticular offenses was often described in general terms like
“malice,” see, e. g., In re Eckart, 166 U. S. 481 (1897); 4 W.
Blackstone, Commentaries *21 (“[A]n unwarrantable act
without a vicious will is no crime at all”), but the modern
tendency has been toward more specific descriptions, as
shown in the Arizona statute defining the murder charged
against Clark: the State had to prove that in acting to kill
the victim, Clark intended to kill a law enforcement officer
on duty or knew that the victim was such an officer on duty.
See generally Gardner, The Mens Rea Enigma: Observations
on the Role of Motive in the Criminal Law Past and Present,
1993 Utah L. Rev. 635. As applied to mens rea (and every
other element), the force of the presumption of innocence is
measured by the force of the showing needed to overcome it,
which is proof beyond a reasonable doubt that a defendant’s
state of mind was in fact what the charge states. See
Winship, supra, at 361–363.
2
The presumption of sanity is equally universal in some va
riety or other, being (at least) a presumption that a defend
ant has the capacity to form the mens rea necessary for a
verdict of guilt and the consequent criminal responsibility.
See Leland, 343 U. S., at 799; Davis v. United States, 160
U. S. 469, 486–487 (1895); M’Naghten’s Case, 10 Cl. & Fin., at
210, 8 Eng. Rep., at 722; see generally 1 LaFave, Substantive
Criminal Law § 8.3(a), at 598–599, and n. 1. This presump
tion dispenses with a requirement on the government’s part

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to include as an element of every criminal charge an allega
tion that the defendant had such a capacity.35 The force of
this presumption, like the presumption of innocence, is meas
ured by the quantum of evidence necessary to overcome it;
unlike the presumption of innocence, however, the force of
the presumption of sanity varies across the many state and
federal jurisdictions, and prior law has recognized consider
able leeway on the part of the legislative branch in defin
ing the presumption’s strength through the kind of evidence
and degree of persuasiveness necessary to overcome it, see
Fisher v. United States, 328 U. S. 463, 466–476 (1946).36
There are two points where the sanity or capacity pre
sumption may be placed in issue. First, a State may allow
a defendant to introduce (and a factfinder to consider) evi
dence of mental disease or incapacity for the bearing it can
have on the government’s burden to show mens rea. See,
e. g., State v. Perez, 882 A. 2d 574, 584 (R. I. 2005).37 In such
States the evidence showing incapacity to form the guilty
state of mind, for example, qualifies the probative force of
other evidence, which considered alone indicates that the de
fendant actually formed the guilty state of mind. If it is
shown that a defendant with mental disease thinks all blond
people are robots, he could not have intended to kill a person
when he shot a man with blond hair, even though he seemed
35 A legislature is nonetheless free to require affirmative proof of sanity
by the way it describes a criminal offense, see Dixon v. United States,
ante, at 9–12.
36 Although a desired evidentiary use is restricted, that is not equivalent
to a Sandstrom presumption. See Sandstrom v. Montana, 442 U. S. 510,
514–524 (1979) (due process forbids use of presumption that relieves the
prosecution of burden of proving mental state by inference of intent from
an act).
37 In fact, Oregon had this scheme in place when we decided Leland v.
Oregon, 343 U. S. 790, 794–796 (1952). We do not, however, read any part
of Leland to require as a matter of due process that evidence of incapacity
be considered to rebut the mens rea element of a crime.

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to act like a man shooting another man.38 In jurisdictions
that allow mental-disease and capacity evidence to be consid
ered on par with any other relevant evidence when deciding
whether the prosecution has proven mens rea beyond a rea
sonable doubt, the evidence of mental disease or incapacity
need only support what the factfinder regards as a reason
able doubt about the capacity to form (or the actual forma
tion of) the mens rea, in order to require acquittal of the
charge. Thus, in these States the strength of the presump
tion of sanity is no greater than the strength of the evidence
of abnormal mental state that the factfinder thinks is enough
to raise a reasonable doubt.
The second point where the force of the presumption of
sanity may be tested is in the consideration of a defense of
insanity raised by a defendant. Insanity rules like M’Nagh
ten and the variants discussed in Part II, supra, are attempts
to define, or at least to indicate, the kinds of mental differ
ences that overcome the presumption of sanity or capacity
and therefore excuse a defendant from customary criminal
responsibility, see Jones v. United States, 463 U. S. 354, 373,
n. 4 (1983) (Brennan, J., dissenting); D. Hermann, The Insan
ity Defense: Philosophical, Historical and Legal Perspectives
4 (1983) (“A central significance of the insanity defense . . .
38 We reject the State’s argument that mens rea and insanity, as cur
rently understood, are entirely distinguishable, so that mental-disease and
capacity evidence relevant to insanity is simply irrelevant to mens rea.
Not only does evidence accepted as showing insanity trump mens rea, but
evidence of behavior close to the time of the act charged may indicate both
the actual state of mind at that time and also an enduring incapacity to
form the criminal state of mind necessary to the offense charged. See
Brief for American Psychiatric Association et al. as Amici Curiae 12–13;
Arenella, The Diminished Capacity and Diminished Responsibility De
fenses: Two Children of a Doomed Marriage, 77 Colum. L. Rev. 827, 834–
835 (1977); cf. Powell v. Texas, 392 U. S. 514, 535–536 (1968) (plurality opin
ion) (the “doctrines of actus reus, mens rea, insanity, mistake, justification,
and duress” are a “collection of interlocking and overlapping concepts
which the common law has utilized to assess the moral accountability of
an individual for his antisocial deeds”).

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is the separation of nonblameworthy from blameworthy
offenders”), even if the prosecution has otherwise overcome
the presumption of innocence by convincing the factfinder
of all the elements charged beyond a reasonable doubt. The
burden that must be carried by a defendant who raises
the insanity issue, again, defines the strength of the san
ity presumption. A State may provide, for example, that
whenever the defendant raises a claim of insanity by some
quantum of credible evidence, the presumption disappears
and the government must prove sanity to a specified degree
of certainty (whether beyond reasonable doubt or something
less). See, e. g., Commonwealth v. Keita, 429 Mass. 843,
846, 712 N. E. 2d 65, 68 (1999). Or a jurisdiction may place
the burden of persuasion on a defendant to prove insanity as
the applicable law defines it, whether by a preponderance of
the evidence or to some more convincing degree, see Ariz.
Rev. Stat. Ann. § 13–502(C) (West 2001); Leland, 343 U. S.,
at 798. In any case, the defendant’s burden defines the pre
sumption of sanity, whether that burden be to burst a bubble
or to show something more.
3
The third principle implicated by Clark’s argument is a
defendant’s right as a matter of simple due process to pre
sent evidence favorable to himself on an element that must
be proven to convict him.39 As already noted, evidence
tending to show that a defendant suffers from mental disease
and lacks capacity to form mens rea is relevant to rebut evi
dence that he did in fact form the required mens rea at the
time in question; this is the reason that Clark claims a right
to require the factfinder in this case to consider testimony
39 Clark’s argument assumes that Arizona’s rule is a rule of evidence,
rather than a redefinition of mens rea, see Montana v. Egelhoff, 518 U. S.
37, 58–59 (1996) (Ginsburg, J., concurring in judgment); id., at 71 (O’Con
nor, J., dissenting). We have no reason to view the rule otherwise, and
on this assumption, it does not violate due process, see infra, at 773–779.

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about his mental illness and his incapacity directly, when
weighing the persuasiveness of other evidence tending to
show mens rea, which the prosecution has the burden to
prove.
As Clark recognizes, however, the right to introduce rele
vant evidence can be curtailed if there is a good reason for
doing that. “While the Constitution . . . prohibits the exclu
sion of defense evidence under rules that serve no legitimate
purpose or that are disproportionate to the ends that they
are asserted to promote, well-established rules of evidence
permit trial judges to exclude evidence if its probative value
is outweighed by certain other factors such as unfair preju
dice, confusion of the issues, or potential to mislead the jury.”
Holmes v. South Carolina, 547 U. S. 319, 326 (2006); see
Crane v. Kentucky, 476 U. S. 683, 689–690 (1986) (permitting
exclusion of evidence that “poses an undue risk of ‘harass
ment, prejudice, [or] confusion of the issues’ ” (quoting Dela
ware v. Van Arsdall, 475 U. S. 673, 679 (1986))); see also Egel
hoff, 518 U. S. 37; Chambers v. Mississippi, 410 U. S. 284,
302 (1973). And if evidence may be kept out entirely, its
consideration may be subject to limitation, which Arizona
claims the power to impose here. State law says that evi
dence of mental disease and incapacity may be introduced
and considered, and if sufficiently forceful to satisfy the de
fendant’s burden of proof under the insanity rule it will dis
place the presumption of sanity and excuse from criminal
responsibility. But mental-disease and capacity evidence
may be considered only for its bearing on the insanity de
fense, and it will avail a defendant only if it is persuasive
enough to satisfy the defendant’s burden as defined by the
terms of that defense. The mental-disease and capacity evi
dence is thus being channeled or restricted to one issue and
given effect only if the defendant carries the burden to con
vince the factfinder of insanity; the evidence is not being ex
cluded entirely, and the question is whether reasons for re
quiring it to be channeled and restricted are good enough to

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satisfy the standard of fundamental fairness that due process
requires. We think they are.
E
1
The first reason supporting the Mott rule is Arizona’s au
thority to define its presumption of sanity (or capacity or
responsibility) by choosing an insanity definition, as dis
cussed in Part II, supra, and by placing the burden of per
suasion on defendants who claim incapacity as an excuse
from customary criminal responsibility. No one, certainly
not Clark here, denies that a State may place a burden of
persuasion on a defendant claiming insanity, see Leland,
supra, at 797–799 (permitting a State, consistent with due
process, to require the defendant to bear this burden). And
Clark presses no objection to Arizona’s decision to require
persuasion to a clear and convincing degree before the pre
sumption of sanity and normal responsibility is overcome.
See Brief for Petitioner 18, n. 25.
But if a State is to have this authority in practice as well
as in theory, it must be able to deny a defendant the opportu
nity to displace the presumption of sanity more easily when
addressing a different issue in the course of the criminal
trial. Yet, as we have explained, just such an opportunity
would be available if expert testimony of mental disease and
incapacity could be considered for whatever a factfinder
might think it was worth on the issue of mens rea.40 As we
mentioned, the presumption of sanity would then be only as
strong as the evidence a factfinder would accept as enough
to raise a reasonable doubt about mens rea for the crime
charged; once reasonable doubt was found, acquittal would
40 Cf. post, at 783 (Kennedy, J., dissenting) (“The psychiatrist’s explana
tion of Clark’s condition was essential to understanding how he processes
sensory data and therefore to deciding what information was in his mind
at the time of the shooting. Simply put, knowledge relies on cognition,
and cognition can be affected by schizophrenia”).

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be required, and the standards established for the defense of
insanity would go by the boards.
Now, a State is of course free to accept such a possibility
in its law. After all, it is free to define the insanity defense
by treating the presumption of sanity as a bursting bubble,
whose disappearance shifts the burden to the prosecution
to prove sanity whenever a defendant presents any credible
evidence of mental disease or incapacity. In States with this
kind of insanity rule, the legislature may well be willing to
allow such evidence to be considered on the mens rea ele
ment for whatever the factfinder thinks it is worth. What
counts for due process, however, is simply that a State that
wishes to avoid a second avenue for exploring capacity, less
stringent for a defendant, has a good reason for confining the
consideration of evidence of mental disease and incapacity to
the insanity defense.
It is obvious that Arizona’s Mott rule reflects such a
choice. The State Supreme Court pointed out that the State
had declined to adopt a defense of diminished capacity
(allowing a jury to decide when to excuse a defendant be
cause of greater than normal difficulty in conforming to the
law).41 The court reasoned that the State’s choice would be
undercut if evidence of incapacity could be considered for
41 Though the term “diminished capacity” has been given different mean
ings, see, e. g., Morse, Undiminished Confusion in Diminished Capacity, 75
J. Crim. L. & C. 1 (1984) (“The diminished capacity doctrine allows a crimi
nal defendant to introduce evidence of mental abnormality at trial either
to negate a mental element of the crime charged, thereby exonerating the
defendant of that charge, or to reduce the degree of crime for which the
defendant may be convicted, even if the defendant’s conduct satisfied all
the formal elements of a higher offense”), California, a jurisdiction with
which the concept has traditionally been associated, understood it to be
simply a “ ‘showing that the defendant’s mental capacity was reduced by
mental illness, mental defect or intoxication,’ ” People v. Berry, 18 Cal. 3d
509, 517, 556 P. 2d 777, 781 (1976) (quoting People v. Castillo, 70 Cal. 2d
264, 270, 449 P. 2d 449, 452 (1969); emphasis deleted), abrogated by Cal.
Penal Code Ann. §§ 25(a), 28(a)–(b), 29 (West 1999 and Supp. 2006).

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whatever a jury might think sufficient to raise a reasonable
doubt about mens rea, even if it did not show insanity. 187
Ariz., at 541, 931 P. 2d, at 1051. In other words, if a jury
were free to decide how much evidence of mental disease and
incapacity was enough to counter evidence of mens rea to the
point of creating a reasonable doubt, that would in functional
terms be analogous to allowing jurors to decide upon some
degree of diminished capacity to obey the law, a degree set
by them, that would prevail as a stand-alone defense.42
2
A State’s insistence on preserving its chosen standard of
legal insanity cannot be the sole reason for a rule like Mott,
however, for it fails to answer an objection the dissent makes
in this case. See post, at 789–797 (opinion of Kennedy, J.).
An insanity rule gives a defendant already found guilty the
opportunity to excuse his conduct by showing he was insane
when he acted, that is, that he did not have the mental capac
ity for conventional guilt and criminal responsibility. But,
as the dissent argues, if the same evidence that affirmatively
shows he was not guilty by reason of insanity (or “guilty
except insane” under Arizona law, Ariz. Rev. Stat. Ann. § 13–
502(A) (West 2001)) also shows it was at least doubtful that
he could form mens rea, then he should not be found guilty
in the first place; it thus violates due process when the State
42 It is beyond question that Arizona may preclude such a defense, see
Fisher v. United States, 328 U. S. 463, 466–476 (1946), and there is no
doubt that the Arizona Legislature meant to do so, see Ariz. Rev. Stat.
Ann. § 13–502(A) (West 2001) (“Mental disease or defect does not include
disorders that result from acute voluntary intoxication or withdrawal from
alcohol or drugs, character defects, psychosexual disorders or impulse con
trol disorders. Conditions that do not constitute legal insanity include
but are not limited to momentary, temporary conditions arising from the
pressure of the circumstances, moral decadence, depravity or passion
growing out of anger, jealousy, revenge, hatred or other motives in a per
son who does not suffer from a mental disease or defect or an abnormality
that is manifested only by criminal conduct”).

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impedes him from using mental-disease and capacity evi
dence directly to rebut the prosecution’s evidence that he did
form mens rea.
Are there, then, characteristics of mental-disease and ca
pacity evidence giving rise to risks that may reasonably be
hedged by channeling the consideration of such evidence to
the insanity issue on which, in States like Arizona, a defend
ant has the burden of persuasion? We think there are: in
the controversial character of some categories of mental dis
ease, in the potential of mental-disease evidence to mislead,
and in the danger of according greater certainty to capacity
evidence than experts claim for it.
To begin with, the diagnosis may mask vigorous debate
within the profession about the very contours of the mental
disease itself. See, e. g., American Psychiatric Association,
Diagnostic and Statistical Manual of Mental Disorders xxxiii
(4th ed. text rev. 2000) (hereinafter DSM–IV–TR) (“DSM–IV
reflects a consensus about the classification and diagnosis of
mental disorders derived at the time of its initial publication.
New knowledge generated by research or clinical experience
will undoubtedly lead to an increased understanding of the
disorders included in DSM–IV, to the identification of new
disorders, and to the removal of some disorders in future
classifications. The text and criteria sets included in
DSM–IV will require reconsideration in light of evolving
new information”); P. Caplan, They Say You’re Crazy: How
the World’s Most Powerful Psychiatrists Decide Who’s Nor
mal (1995) (criticism by former consultant to the DSM
against some of the DSM’s categories). And Members of
this Court have previously recognized that the end of such
debate is not imminent. See Jones, 463 U. S., at 365, n. 13
(“ ‘The only certain thing that can be said about the present
state of knowledge and therapy regarding mental disease is
that science has not reached finality of judgment’ ” (quoting
Greenwood v. United States, 350 U. S. 366, 375 (1956))); Pow
ell v. Texas, 392 U. S. 514, 537 (1968) (plurality opinion) (“It

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is simply not yet the time to write into the Constitution for
mulas cast in terms whose meaning, let alone relevance, is
not yet clear . . . to doctors”). Though we certainly do not
“condem[n mental-disease evidence] wholesale,” Brief for
American Psychiatric Association et al. as Amici Curiae 15,
the consequence of this professional ferment is a general cau
tion in treating psychological classifications as predicates for
excusing otherwise criminal conduct.
Next, there is the potential of mental-disease evidence to
mislead jurors (when they are the factfinders) through the
power of this kind of evidence to suggest that a defendant
suffering from a recognized mental disease lacks cognitive,
moral, volitional, or other capacity, when that may not be a
sound conclusion at all. Even when a category of mental
disease is broadly accepted and the assignment of a defend
ant’s behavior to that category is uncontroversial, the classi
fication may suggest something very significant about a de
fendant’s capacity, when in fact the classification tells us little
or nothing about the ability of the defendant to form mens
rea or to exercise the cognitive, moral, or volitional capac
ities that define legal sanity.43 See DSM–IV–TR xxxii–
xxxiii (“When the DSM–IV categories, criteria, and textual
descriptions are employed for forensic purposes, there are
significant risks that diagnostic information will be misused
or misunderstood. These dangers arise because of the im
perfect fit between the questions of ultimate concern to the
law and the information contained in a clinical diagnosis. In
most situations, the clinical diagnosis of a DSM–IV mental
disorder is not sufficient to establish the existence for legal
43 Our observation about the impact of mental-disease evidence on un
derstandings of capacity in no way undermines the assertion by the Amer
ican Psychiatric Association, the American Psychological Association, and
the American Academy of Psychiatry in this case that “[e]xpert evidence
of mental disorders . . . is . . . relevant to the mental-state issues raised
by mens rea requirements,” Brief for American Psychiatric Association
et al. as Amici Curiae 15.

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purposes of . . . ‘mental diseas[e]’ or ‘mental defect.’ In de
termining whether an individual meets a specified legal
standard (e. g., for . . . criminal responsibility . . . ), additional
information is usually required beyond that contained in the
DSM–IV diagnosis”). The limits of the utility of a profes
sional disease diagnosis are evident in the dispute between
the two testifying experts in this case; they agree that Clark
was schizophrenic, but they come to opposite conclusions on
whether the mental disease in his particular case left him
bereft of cognitive or moral capacity. Evidence of mental
disease, then, can easily mislead; it is very easy to slide from
evidence that an individual with a professionally recognized
mental disease is very different, into doubting that he has
the capacity to form mens rea, whereas that doubt may not
be justified. And of course, in the cases mentioned before,
in which the categorization is doubtful or the category of
mental disease is itself subject to controversy, the risks are
even greater that opinions about mental disease may confuse
a jury into thinking the opinions show more than they do.
Because allowing mental-disease evidence on mens rea can
thus easily mislead, it is not unreasonable to address that
tendency by confining consideration of this kind of evidence
to insanity, on which a defendant may be assigned the burden
of persuasion.
There are, finally, particular risks inherent in the opinions
of the experts who supplement the mental-disease classifica
tions with opinions on incapacity: on whether the mental dis
ease rendered a particular defendant incapable of the cogni
tion necessary for moral judgment or mens rea or otherwise
incapable of understanding the wrongfulness of the conduct
charged. Unlike observational evidence bearing on mens
rea, capacity evidence consists of judgment, and judgment
fraught with multiple perils: a defendant’s state of mind at
the crucial moment can be elusive no matter how conscien
tious the enquiry, and the law’s categories that set the terms
of the capacity judgment are not the categories of psychology

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that govern the expert’s professional thinking. Although
such capacity judgments may be given in the utmost good
faith, their potentially tenuous character is indicated by the
candor of the defense expert in this very case. Contrary to
the State’s expert, he testified that Clark lacked the capacity
to appreciate the circumstances realistically and to under
stand the wrongfulness of what he was doing, App. 48–49,
but he said that “no one knows exactly what was on [his]
mind” at the time of the shooting, id., at 48. And even when
an expert is confident that his understanding of the mind is
reliable, judgment addressing the basic categories of capac
ity requires a leap from the concepts of psychology, which
are devised for thinking about treatment, to the concepts of
legal sanity, which are devised for thinking about criminal
responsibility. See Insanity Defense Work Group, American
Psychiatric Association Statement on the Insanity Defense,
140 Am. J. Psychiatry 681, 686 (1983), reprinted in 2 The Role
of Mental Illness in Criminal Trials 117, 122 (J. Moriarty ed.
2001) (“The American Psychiatric Association is not opposed
to legislatures restricting psychiatric testimony about the . . .
ultimate legal issues concerning the insanity defense. . . .
When . . . ‘ultimate issue’ questions are formulated by the
law and put to the expert witness who must then say ‘yea’
or ‘nay,’ then the expert witness is required to make a leap
in logic. He no longer addresses himself to medical concepts
but instead must infer or intuit what is in fact unspeakable,
namely, the probable relationship between medical concepts
and legal or moral constructs such as free will. These im
permissible leaps in logic made by expert witnesses confuse
the jury. . . . This state of affairs does considerable injustice
to psychiatry and, we believe, possibly to criminal defend
ants. These psychiatric disagreements . . . cause less than
fully understanding juries or the public to conclude that psy
chiatrists cannot agree. In fact, in many criminal insanity
trials both prosecution and defense psychiatrists do agree
about the nature and even the extent of mental disorder ex

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Opinion of the Court
hibited by the defendant at the time of the act” (emphasis
in original; footnote omitted)); DSM–IV–TR xxxii–xxxiii; P.
Giannelli & E. Imwinkelried, Scientific Evidence § 9–3(B),
p. 286 (1986) (“[N]o matter how the test for insanity is
phrased, a psychiatrist or psychologist is no more qualified
than any other person to give an opinion about whether a
particular defendant’s mental condition satisfies the legal
test for insanity”); cf. R. Slovenko, Psychiatry and Criminal
Culpability 55 (1995) (“The scope of the DSM is wide-ranging
and includes ‘conduct disorders’ but ‘evil’ is not mentioned”).
In sum, these empirical and conceptual problems add up to
a real risk that an expert’s judgment in giving capacity evi
dence will come with an apparent authority that psycholo
gists and psychiatrists do not claim to have. We think that
this risk, like the difficulty in assessing the significance of
mental-disease evidence, supports the State’s decision to
channel such expert testimony to consideration on the insan
ity defense, on which the party seeking the benefit of this
evidence has the burden of persuasion.
It bears repeating that not every State will find it worth
while to make the judgment Arizona has made, and the
choices the States do make about dealing with the risks
posed by mental-disease and capacity evidence will reflect
their varying assessments about the presumption of sanity
as expressed in choices of insanity rules.44 The point here
simply is that Arizona has sensible reasons to assign the
risks as it has done by channeling the evidence.45
44 A State in which the burden of persuasion as to a defendant’s sanity
lies with the prosecution might also be justified in restricting mental
disease and capacity evidence to insanity determinations owing to the po
tential of mental-disease evidence to mislead and the risk of misjudgment
inherent in capacity evidence. We need not, in the context of this case,
address that issue.
45 Arizona’s rule is supported by a further practical reason, though not
as weighty as those just considered. As mentioned before, if substantial
mental-disease and capacity evidence is accepted as rebutting mens rea in
a given case, the affirmative defense of insanity will probably not be

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Opinion of Breyer, J.
F
Arizona’s rule serves to preserve the State’s chosen stand
ard for recognizing insanity as a defense and to avoid con
fusion and misunderstanding on the part of jurors.46 For
these reasons, there is no violation of due process under
Chambers and its progeny, and no cause to claim that chan
neling evidence on mental disease and capacity offends any
“ ‘principle of justice so rooted in the traditions and con
science of our people as to be ranked as fundamental,’ ” Pat
terson, 432 U. S., at 202 (quoting Speiser, 357 U. S., at 523).
* * *
The judgment of the Court of Appeals of Arizona is, ac
cordingly, affirmed.
It is so ordered.
Justice Breyer, concurring in part and dissenting in
part.
As I understand the Court’s opinion, it distinguishes
among three categories of evidence related to insanity: (1)
fact-related evidence as to the defendant’s specific state of
mind at the time of the crime, e. g., evidence that shows he
reached or ruled upon; the defendant will simply be acquitted (or perhaps
convicted of a lesser included offense). If an acquitted defendant suffers
from a mental disease or defect that makes him dangerous, he will neither
be confined nor treated psychiatrically unless a judge so orders after some
independent commitment proceeding. But if a defendant succeeds in
showing himself insane, Arizona law (and presumably that of every other
State with an insanity rule) will require commitment and treatment as a
consequence of that finding without more. It makes sense, then, to chan
nel capacity evidence to the issue structured to deal with mental incapac
ity when such a claim is raised successfully. See, e. g., Jones, 463 U. S., at
368 (“The purpose of commitment following an insanity acquittal . . . is to
treat the individual’s mental illness and protect him and society from his
potential dangerousness”).
46 The rule also deals in a practical way with those whose insanity has
been shown to make them dangerous to others. See n. 45, supra.

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Opinion of Breyer, J.
thought the policeman was not a human being; (2) expert
opinion evidence that the defendant suffered from a mental
disease that would have affected his capacity to form an in
tent to kill a policeman, e. g., that he suffers from a disease
of a kind where powerful voices command the sufferer to kill;
and (3) expert opinion evidence that the defendant was le
gally insane, e. g., evidence that he did not know right from
wrong. Ante, at 757–759.
I agree with the Court’s basic categorization. I also agree
that the Constitution permits a State to provide for consider
ation of the second and third types of evidence solely in con
junction with the insanity defense. A State might reason
ably fear that, without such a rule, the types of evidence as
to intent would become confused in the jury’s mind, indeed
that in some cases the insanity question would displace the
intent question as the parties litigate both simultaneously.
Nonetheless, I believe the distinction among these kinds
of evidence will be unclear in some cases. And though I
accept the majority’s reading of the record, I remain con
cerned as to whether the lower courts, in setting forth and
applying State v. Mott, 187 Ariz. 536, 931 P. 2d 1046, cert.
denied, 520 U. S. 1234 (1997), focused with sufficient direct
ness and precision upon the distinction.
Consequently, I would remand this case so that Arizona’s
courts can determine whether Arizona law, as set forth in
Mott and other cases, is consistent with the distinction the
Court draws and whether the trial court so applied Arizona
law here. I would also reserve the question (as I believe
the Court has done) as to the burden of persuasion in a case
where the defendant produces sufficient evidence of the sec
ond kind as to raise a reasonable doubt suggesting that he
suffered from a mental illness so severe as to prevent him
from forming any relevant intent at all.
For this reason, I dissent only from Parts III–B and III–C
of the Court’s opinion and the ultimate disposition of this
case, and I join the remainder.

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Kennedy, J., dissenting
Justice Kennedy, with whom Justice Stevens and
Justice Ginsburg join, dissenting.
In my submission the Court is incorrect in holding that
Arizona may convict petitioner Eric Clark of first-degree
murder for the intentional or knowing killing of a police offi
cer when Clark was not permitted to introduce critical and
reliable evidence showing he did not have that intent or
knowledge. The Court is wrong, too, when it concludes the
issue cannot be reached because of an error by Clark’s coun
sel. Its reasons and conclusions lead me to file this respect
ful dissent.
Since I would reverse the judgment of the Arizona Court
of Appeals on this ground, and the Arizona courts might well
alter their interpretation of the State’s criminal responsibil
ity statute were my rationale to prevail, it is unnecessary
for me to address the argument that Arizona’s definition of
insanity violates due process.
I
Clark claims that the trial court erred in refusing to con
sider evidence of his chronic paranoid schizophrenia in decid
ing whether he possessed the knowledge or intent required
for first-degree murder. Seizing upon a theory invented
here by the Court itself, the Court narrows Clark’s claim
so he cannot raise the point everyone else thought was
involved in the case. The Court says the only issue before
us is whether there is a right to introduce mental-disease
evidence or capacity evidence, not a right to introduce ob
servation evidence. See ante, at 756–765. This restruc
tured evidentiary universe, with no convincing authority to
support it, is unworkable on its own terms. Even were that
not so, however, the Court’s tripartite structure is something
not addressed by the state trial court, the state appellate
court, counsel on either side in those proceedings, or the
briefs the parties filed with us. The Court refuses to con
sider the key part of Clark’s claim because his counsel did

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Kennedy, J., dissenting
not predict the Court’s own invention. It is unrealistic, and
most unfair, to hold that Clark’s counsel erred in failing to
anticipate so novel an approach. If the Court is to insist on
its approach, at a minimum the case should be remanded to
determine whether Clark is bound by his counsel’s pur
ported waiver.
The Court’s error, of course, has significance beyond this
case. It adopts an evidentiary framework that, in my view,
will be unworkable in many cases. The Court classifies
Clark’s behavior and expressed beliefs as observation evi
dence but insists that its description by experts must be
mental-disease evidence or capacity evidence. See ante, at
757–759. These categories break down quickly when it is
understood how the testimony would apply to the question
of intent and knowledge at issue here. The most common
type of schizophrenia, and the one Clark suffered from, is
paranoid schizophrenia. See P. Berner et al., Diagnostic
Criteria for Functional Psychoses 37 (2d ed. 1992). The ex
istence of this functional psychosis is beyond dispute, but
that does not mean the lay witness understands it or that a
disputed issue of fact concerning its effect in a particular
instance is not something for the expert to address. Com
mon symptoms of the condition are delusions accompanied
by hallucinations, often of the auditory type, which can cause
disturbances of perception. Ibid. Clark’s expert testified
that people with schizophrenia often play radios loudly to
drown out the voices in their heads. See App. 32. Clark’s
attorney argued to the trial court that this, rather than a
desire to lure a policeman to the scene, explained Clark’s
behavior just before the killing. Id., at 294–295. The ob
servation that schizophrenics play radios loudly is a fact re
garding behavior, but it is only a relevant fact if Clark has
schizophrenia.
Even if this evidence were, to use the Court’s term,
mental-disease evidence, because it relies on an expert opin
ion, what would happen if the expert simply were to testify,
without mentioning schizophrenia, that people with Clark’s

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Kennedy, J., dissenting
symptoms often play the radio loudly? This seems to be
factual evidence, as the term is defined by the Court, yet it
differs from mental-disease evidence only in forcing the wit
ness to pretend that no one has yet come up with a way to
classify the set of symptoms being described. More gener
ally, the opinion that Clark had paranoid schizophrenia—an
opinion shared by experts for both the prosecution and de
fense—bears on efforts to determine, as a factual matter,
whether he knew he was killing a police officer. The psychi
atrist’s explanation of Clark’s condition was essential to un
derstanding how he processes sensory data and therefore to
deciding what information was in his mind at the time of the
shooting. Simply put, knowledge relies on cognition, and
cognition can be affected by schizophrenia. See American
Psychiatric Association, Diagnostic and Statistical Manual of
Mental Disorders 299 (4th ed. text rev. 2000) (“The charac
teristic symptoms of Schizophrenia involve a range of cogni
tive and emotional dysfunctions that include perception”);
ibid. (Symptoms include delusions, which are “erroneous be
liefs that usually involve a misinterpretation of perceptions
or experiences”). The mental-disease evidence at trial was
also intertwined with the observation evidence because it
lent needed credibility. Clark’s parents and friends testified
Clark thought the people in his town were aliens trying to
kill him. These claims might not be believable without a
psychiatrist confirming the story based on his experience
with people who have exhibited similar behaviors. It makes
little sense to divorce the observation evidence from the ex
planation that makes it comprehensible.
Assuming the Court’s tripartite structure were feasible,
the Court is incorrect when it narrows Clark’s claim to ex
clude any concern about observation evidence. In deciding
Clark’s counsel failed to raise this issue, the Court relies on
a series of perceived ambiguities regarding how the claim
fits within the Court’s own categories. See ante, at 761–765.
The Court cites no precedent for construing these ambigu
ities against the claimant and no prudential reason for ignor

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784 CLARK v. ARIZONA
Kennedy, J., dissenting
ing the breadth of Clark’s claim. It is particularly surpris
ing that the Court does so to the detriment of a criminal
defendant asserting the fundamental challenge that the trier
of fact refused to consider critical evidence showing he is
innocent of the crime charged.
The alleged ambiguities are, in any event, illusory. The
evidence at trial addressed more than the question of general
incapacity or opinions regarding mental illness; it went fur
ther, as it included so-called observation evidence relevant
to Clark’s mental state at the moment he shot the officer.
There was testimony, for example, that Clark thought the
people in his town, particularly government officials, were
not human beings but aliens who were trying to kill him.
See App. 119–121, 131–132, 192–197, 249–256; Tr. of Bench
Trial in No. CR 2000–538, pp. 110–112, 131–132, 136, 226–228
(Aug. 20, 2003); id., at 24–25, 59–60 (Aug. 21, 2003). The
Court recognizes the existence of this essential observation
evidence. See ante, at 757–759.
The Court holds, nonetheless, that “we cannot be sure”
whether the trial court failed to consider this evidence.
Ante, at 764–765. It is true the trial court ruling was not
perfectly clear. Its language does strongly suggest, though,
that it did not consider any of this testimony in deciding
whether Clark had the knowledge or intent required for
first-degree murder. After recognizing that “much of the
evidence that [the defense is] going to be submitting, in fact
all of it, as far as I know . . . that has to do with the insanity
could also arguably be made . . . as to form and intent and
his capacity for the intent,” the court concluded “we will be
focusing, as far as I’m concerned, strictly on the insanity de
fense.” App. 9. In announcing its verdict, the trial court
did not mention any of the mental-illness evidence, observa
tion or otherwise, in deciding Clark’s guilt. Id., at 331–335.
The most reasonable assumption, then, would seem to be
that the trial court did not consider it, and the Court does
not hold otherwise. See ante, at 760–761.

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Clark’s objection to this refusal by the trier of fact to con
sider the evidence as it bore on his key defense was made at
all stages of the proceeding. In his post-trial motion to va
cate the judgment, Clark argued that “prohibiting consider
ation of any evidence reflecting upon a mentally ill criminal
defendant’s ability to form the necessary mens rea violates
due process.” Record, Doc. 406, p. 8. Clark pressed the
same argument in the Arizona Court of Appeals. See Ap
pellant’s Opening Brief in No. 1CA–CR–03–0851 etc.,
pp. 46–52 (hereinafter Appellant’s Opening Brief). He also
noted that the trial judge had erred in refusing to consider
nonexpert testimony—presumably what the Court would
call observation evidence—on Clark’s mental illness. Id., at
47–48 (“The trial court therefore violated [Clark’s] right to
present a defense because [the] court refused to consider any
evidence, including the multiple testimonials of lay witnesses
. . . in deciding whether he could form the requisite mens
rea”). The appeals court decided the issue on the merits,
holding that the trial court was correct not to consider
the evidence of mental illness in determining whether Clark
had the mens rea for first-degree murder. See App. 351–
353. It offered no distinction at all between observation or
mental-disease evidence.
Notwithstanding the appeals court’s decision, the Court
states that the issue was not clearly presented to the state
courts. See ante, at 762–765. According to the Court,
Clark only raised an objection based on State v. Mott,
187 Ariz. 536, 931 P. 2d 1046 (1997), cert. denied, 520 U. S.
1234 (1997), see ante, at 762–765, and Mott’s holding was
limited to the exclusion of mental-disease and capacity
evidence, see ante, at 760. The Court is incorrect, and on
both counts.
First, Clark’s claim goes well beyond an objection to Mott.
In fact, he specifically attempted to distinguish Mott by not
ing that the trial court in this case refused to consider all
evidence of mental illness. See Record, Doc. 406, at 8; see

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also Appellant’s Opening Brief 48. The Court notices these
arguments but criticizes Clark’s counsel for not being specific
about the observation evidence he wanted the trial court to
consider. See ante, at 763. There was no reason, though,
for Clark’s counsel to believe additional specificity was re
quired, since there was no evident distinction in Arizona law
between observation evidence and mental-disease testimony.
Second, Mott’s holding was not restricted to mental
disease evidence. The Arizona Supreme Court did not refer
to any distinction between observation and mental-disease
evidence, or lay and expert testimony. Its holding was
stated in broad terms: “Arizona does not allow evidence of a
defendant’s mental disorder short of insanity either as an
affirmative defense or to negate the mens rea element of a
crime.” 187 Ariz., at 541, 931 P. 2d, at 1051; see id., at 540,
931 P. 2d, at 1050 (“The legislature’s decision . . . evidences
its rejection of the use of psychological testimony to chal
lenge the mens rea element of a crime”). The Court at
tempts to divine a fact/opinion distinction in Mott based on
Mott’s distinguishing a case, State v. Christensen, 129 Ariz.
32, 628 P. 2d 580 (1981), where evidence about behavioral
tendencies was deemed admissible. See ante, at 760.
Christensen, though, also addressed an expert opinion; the
difference was that the evidence there concerned a “charac
ter trait of acting reflexively in response to stress,” not a
mental illness. Mott, supra, at 544, 931 P. 2d, at 1054.
Since the Court recognizes the Arizona Court of Appeals
relied on Mott, the expansive rule of exclusion in Mott—
without any suggestion of a limitation depending on the kind
of evidence—should suffice for us to reach the so-called
observation-evidence issue. Even if, as the Court contends,
see ante, at 760, Mott is limited to expert testimony, the
Court’s categories still do not properly interpret Mott, be
cause the Court’s own definition of observation evidence in
cludes some expert testimony, see ante, at 757–758.
It makes no difference that in the appeals court Clark re
ferred to the issue as inability to form knowledge or intent.

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Kennedy, J., dissenting
See Appellant’s Opening Brief 46–52. He did not insist on
some vague, general incapacity. He stated, instead, that he
“suffered from a major mental illness and was psychotic at
the time of the offense.” Id., at 48. Even if Clark’s argu
ments were insufficient to apprise the state court of the ar
gument, “[o]ur traditional rule is that ‘[o]nce a federal claim
is properly presented, a party can make any argument in
support of that claim; parties are not limited to the precise
arguments they made below.’ ” Lebron v. National Rail
road Passenger Corporation, 513 U. S. 374, 379 (1995) (quot
ing Yee v. Escondido, 503 U. S. 519, 534 (1992)). The claim
is clear. Though it seems to be obscure to this Court, it was
understood by the Arizona Court of Appeals, which stated:
“Clark argues that the trial court erred in refusing to con
sider evidence of his mental disease or defect in determining
whether he had the requisite mens rea to commit first
degree murder.” App. 351. When the question is what the
state court held, it is not instructive for this Court to recast
the words the state court used.
The razor-thin distinction the Court draws between evi
dence being used to show incapacity and evidence being used
to show lack of mens rea directly does not identify two dif
ferent claims. Clark’s single claim, however characterized,
involves the use of the same mental-illness evidence to de
cide whether he had the requisite knowledge or intent. The
various ways in which the evidence is relevant in disproving
mens rea hardly qualify as separate claims. The new argu
ments allowed in Lebron and Yee, by comparison, were far
more disconnected from the initial bases for the alleged vio
lations. See Lebron, supra, at 378, 379 (for purposes of
showing state action, petitioner could argue that Amtrak
was a Government entity even though he argued below only
that it was a private entity with close connections to Govern
ment entities, because the claim was simply “that Amtrak
did not accord him the rights it was obliged to provide by
the First Amendment”); Yee, supra, at 534, 535 (petitioners

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Kennedy, J., dissenting
could argue that an ordinance constituted a regulatory tak
ing, even though they arguably asserted in the Court of Ap
peals only a physical taking, because the claim was simply
“that the ordinance effects an unconstitutional taking”). If
we give this latitude to litigants in civil cases, surely we
must do so here. Furthermore, to the extent any ambiguity
remains on whether the claim was raised, the proper course
is to remand. See Bradshaw v. Richey, 546 U. S. 74, 80
(2005) (per curiam). Unless the state court clearly decides
an issue on state-law grounds, which the Court does not con
tend occurred here, there is no bar to our review of the fed
eral question. See Harris v. Reed, 489 U. S. 255, 261–262
(1989).
Before this Court Clark framed the issue in broad terms
that encompass the question whether the evidence of his
mental illness should have been considered to show he did
not at the time of the offense have the knowledge or intent to
shoot a police officer. See Brief for Petitioner i (“Questions
Presented for Review (1) Whether Arizona’s blanket exclu
sion of evidence and refusal to consider mental disease or
defect to rebut the state’s evidence on the element of mens
rea violated Petitioner’s right to due process under the
United States Constitution, Fourteenth Amendment?”), 22
(“Here, the trial court held that under the Mott rule it was
obliged to find as a fact that [Clark] knew he was shooting a
police officer to death—a necessary factual element of the
only form of first degree murder charged against [Clark]—
while simultaneously refusing to consider [Clark’s] evidence
that an acute episode of his chronic paranoid schizophrenic
illness prevented him from actually having that knowledge”
(emphasis deleted)), 31–32 (the Arizona courts erred in hold
ing Clark “could be punished as though he had this knowl
edge and intent although he may not in fact have had
either”); Reply Brief for Petitioner 3 (challenging the trial
judge’s refusal “to give any consideration to the mental
illness evidence in making his factual findings as to whether

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Kennedy, J., dissenting
[Clark] did or did not act with the state of mind required
for a first-degree murder conviction”). An entire section of
Clark’s opening brief argues that the evidence of mental ill
ness should have been considered to rebut the prosecution’s
inference of knowledge or intent from the factual circum
stances of the crime. See Brief for Petitioner 13–21. This
line of argument concerns facts of behavior and amounts to
more than a claim of general incapacity.
Clark seeks resolution of issues that can be complex and
somewhat overlapping. In the end, however, we must de
cide whether he had the right to introduce evidence showing
he lacked the intent or knowledge the statute itself sets forth
in describing a basic element of the crime. Clark has pre
served this issue at all stages, including in this Court.
II
Clark was charged with first-degree murder for the shoot
ing of Officer Jeffrey Moritz. “A person commits first
degree murder if,” as relevant here, “[i]ntending or knowing
that the person’s conduct will cause death to a law enforce
ment officer, the person causes the death of a law enforce
ment officer who is in the line of duty.” Ariz. Rev. Stat.
Ann. § 13–1105(A)(3) (West Supp. 2005). Clark challenges
the trial court’s refusal to consider any evidence of mental
illness, from lay or expert testimony, in determining whether
he acted with the knowledge or intent element of the crime.
See App. 9; see also Mott, 187 Ariz., at 541, 931 P. 2d, at 1051.
States have substantial latitude under the Constitution to
define rules for the exclusion of evidence and to apply those
rules to criminal defendants. See United States v. Scheffer,
523 U. S. 303, 308 (1998). This authority, however, has con
stitutional limits. “ ‘Whether rooted directly in the Due
Process Clause of the Fourteenth Amendment or in the Com
pulsory Process or Confrontation Clauses of the Sixth
Amendment, the Constitution guarantees criminal defend
ants “a meaningful opportunity to present a complete de

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Kennedy, J., dissenting
fense.” ’ ” Holmes v. South Carolina, 547 U. S. 319, 324
(2006) (quoting Crane v. Kentucky, 476 U. S. 683, 690 (1986),
in turn quoting California v. Trombetta, 467 U. S. 479, 485
(1984)). “This right is abridged by evidence rules that
‘infring[e] upon a weighty interest of the accused’ and are
‘ “arbitrary” or “disproportionate to the purposes they are
designed to serve.” ’ ” Holmes, supra, at 324 (quoting Schef
fer, supra, at 308, in turn citing and quoting Rock v. Arkan
sas, 483 U. S. 44, 58, 56 (1987)).
The central theory of Clark’s defense was that his schizo
phrenia made him delusional. He lived in a universe where
the delusions were so dominant, the theory was, that he had
no intent to shoot a police officer or knowledge he was doing
so. It is one thing to say he acted with intent or knowledge
to pull the trigger. It is quite another to say he pulled the
trigger to kill someone he knew to be a human being and a
police officer. If the trier of fact were to find Clark’s evi
dence sufficient to discount the case made by the State,
which has the burden to prove knowledge or intent as an
element of the offense, Clark would not be guilty of first
degree murder under Arizona law.
The Court attempts to diminish Clark’s interest by treat
ing mental-illness evidence as concerning only “judgment,”
rather than fact. Ante, at 776–777. This view appears to
derive from the Court’s characterization of Clark’s claim as
raising only general incapacity. See ibid. This is wrong for
the reasons already discussed. It fails to recognize, more
over, the meaning of the offense element in question here.
The mens rea element of intent or knowledge may, at some
level, comprise certain moral choices, but it rests in the first
instance on a factual determination. That is the fact Clark
sought to put in issue. Either Clark knew he was killing a
police officer or he did not.
The issue is not, as the Court insists, whether Clark’s men
tal illness acts as an “excuse from customary criminal re
sponsibility,” ante, at 771, but whether his mental illness, as

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Kennedy, J., dissenting
a factual matter, made him unaware that he was shooting a
police officer. If it did, Clark needs no excuse, as then he
did not commit the crime as Arizona defines it. For the ele
ments of first-degree murder, where the question is knowl
edge of particular facts—that one is killing a police officer—
the determination depends not on moral responsibility but
on empirical fact. Clark’s evidence of mental illness had a
direct and substantial bearing upon what he knew, or
thought he knew, to be the facts when he pulled the trigger;
this lay at the heart of the matter.
The trial court’s exclusion was all the more severe because
it barred from consideration on the issue of mens rea all this
evidence, from any source, thus preventing Clark from show
ing he did not commit the crime as defined by Arizona law.
Quite apart from due process principles, we have held that a
bar of this sort can be inconsistent with the Confrontation
Clause. See Delaware v. Van Arsdall, 475 U. S. 673 (1986).
In Van Arsdall the Court held a state court erred in making
a ruling that “prohibited all inquiry into” an event. Id., at
679. At issue was a line of defense questioning designed to
show the bias of a prosecution witness. In the instant case
the ruling in question bars from consideration all testimony
from all witnesses necessary to present the argument that
was central to the whole case for the defense: a challenge to
the State’s own proof on an element of the crime. The Due
Process and Compulsory Process Clauses, and not the Con
frontation Clause, may be the controlling standard; but the
disability imposed on the accused is every bit as substantial
and pervasive here as it was in Van Arsdall.
Arizona’s rule is problematic because it excludes evidence
no matter how credible and material it may be in disproving
an element of the offense. The Court’s cases have noted the
potential arbitrariness of per se exclusions and, on this ra
tionale, have invalidated various state prohibitions. See
Holmes, supra, at 329 (rule excluding, in certain cases, evi
dence that a third party may have committed the crime

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Kennedy, J., dissenting
“even if that evidence, if viewed independently, would have
great probative value and even if it would not pose an undue
risk of harassment, prejudice, or confusion of the issues”);
Rock, supra, at 56 (rule excluding all hypnotically refreshed
testimony “operates to the detriment of any defendant who
undergoes hypnosis, without regard to the reasons for it, the
circumstances under which it took place, or any independent
verification of the information it produced”); Washington v.
Texas, 388 U. S. 14, 22 (1967) (rule excluding accomplice testi
mony “prevent[s] whole categories of defense witnesses from
testifying on the basis of a priori categories that presume
them unworthy of belief ”).
This is not to suggest all general rules on the exclusion of
certain types of evidence are invalid. If the rule does not
substantially burden the defense, then it is likely permis
sible. See Scheffer, 523 U. S., at 316–317 (upholding exclu
sion of polygraph evidence in part because this rule “does
not implicate any significant interest of the accused”); id.,
at 318 (Kennedy, J., concurring in part and concurring in
judgment) (“[S]ome later case might present a more compel
ling case for introduction of the testimony than this one
does”). Where, however, the burden is substantial, the
State must present a valid reason for its per se evidentiary
rule.
In the instant case Arizona’s proposed reasons are insuffi
cient to support its categorical exclusion. While the State
contends that testimony regarding mental illness may be too
incredible or speculative for the jury to consider, this does
not explain why the exclusion applies in all cases to all evi
dence of mental illness. “A State’s legitimate interest in
barring unreliable evidence does not extend to per se exclu
sions that may be reliable in an individual case.” Rock,
supra, at 61. States have certain discretion to bar unrelia
ble or speculative testimony and to adopt rules to ensure
the reliability of expert testimony. Arizona has done so, and
there is no reason to believe its rules are insufficient to avoid

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Kennedy, J., dissenting
speculative evidence of mental illness. See Ariz. Rules
Evid. 403, 702 (2006). This is particularly true because Ari
zona applies its usual case-by-case approach to permit admis
sion of evidence of mental illness for a variety of other pur
poses. See, e. g., State v. Lindsey, 149 Ariz. 472, 474–475,
720 P. 2d 73, 75–76 (1986) (en banc) (psychological character
istics of molestation victims); State v. Hamilton, 177 Ariz.
403, 408–410, 868 P. 2d 986, 991–993 (App. 1993) (psychologi
cal evidence of child abuse accommodation syndrome); Horan
v. Industrial Comm’n of Ariz., 167 Ariz. 322, 325–326, 806
P. 2d 911, 914–915 (App. 1991) (psychiatric testimony regard
ing neurological deficits).
The risk of jury confusion also fails to justify the rule.
The State defends its rule as a means to avoid the complexi
ties of determining how and to what degree a mental illness
affects a person’s mental state. The difficulty of resolving
a factual issue, though, does not present a sufficient reason
to take evidence away from the jury even when it is crucial
for the defense. “We have always trusted juries to sort
through complex facts in various areas of law.” United
States v. Booker, 543 U. S. 220, 289 (2005) (Stevens, J., dis
senting in part). Even were the risk of jury confusion real
enough to justify excluding evidence in most cases, this
would provide little basis for prohibiting all evidence of men
tal illness without any inquiry into its likely effect on the
jury or its role in deciding the linchpin issue of knowledge
and intent. Indeed, Arizona has a rule in place to serve this
very purpose. See Rule 403.
Even assuming the reliability and jury-confusion justifica
tions were persuasive in some cases, they would not suffice
here. It does not overcome the constitutional objection to
say that an evidentiary rule that is reasonable on its face can
be applied as well to bar significant defense evidence without
any rational basis for doing so. In Van Arsdall, for exam
ple, the Court rejected the application of Delaware Rule of
Evidence 403, which allows relevant evidence to be excluded

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Kennedy, J., dissenting
where its probative value is substantially outweighed by the
risk of unfair prejudice or other harms to the trial process.
475 U. S., at 676, and n. 2. While the Rule is well estab
lished and designed for a legitimate function, the Constitu
tion prevented an application that deprived the defendant of
all inquiry into an important issue. Id., at 679. Other cases
have applied this same case-specific analysis in deciding the
legitimacy of an exclusion. See, e. g., Rock, 483 U. S., at 62
(the “circumstances present an argument for admissibility of
petitioner’s testimony in this particular case, an argument
that must be considered by the trial court”); Chambers v.
Mississippi, 410 U. S. 284, 302 (1973) (“In these circum
stances, where constitutional rights directly affecting the as
certainment of guilt are implicated, the hearsay rule may
not be applied mechanistically to defeat the ends of justice”);
cf. Scheffer, supra, at 318 (Kennedy, J., concurring in part
and concurring in judgment).
The Court undertakes little analysis of the interests par
ticular to this case. By proceeding in this way it devalues
Clark’s constitutional rights. The reliability rationale has
minimal applicability here. The Court is correct that many
mental diseases are difficult to define and the subject of
great debate. See ante, at 774–775. Schizophrenia, how
ever, is a well-documented mental illness, and no one seri
ously disputes either its definition or its most prominent clin
ical manifestations. The State’s own expert conceded that
Clark had paranoid schizophrenia and was actively psychotic
at the time of the killing. See App. 254–257. The jury
confusion rationale, if it is at all applicable here, is the result
of the Court’s own insistence on conflating the insanity de
fense and the question of intent. Considered on its own
terms, the issue of intent and knowledge is a straightforward
factual question. A trier of fact is quite capable of weighing
defense testimony and then determining whether the ac
cused did or did not intend to kill or knowingly kill a human
being who was a police officer. True, the issue can be diffi

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Kennedy, J., dissenting
cult to decide in particular instances, but no more so than
many matters juries must confront.
The Court says mental-illness evidence “can easily mis
lead,” ante, at 776, and may “tel[l] us little or nothing about
the ability of the defendant to form mens rea,” ante, at 775.
These generalities do not, however, show how relevant or
misleading the evidence in this case would be (or explain why
Arizona Rule of Evidence 403 is insufficient for weighing
these factors). As explained above, the evidence of Clark’s
mental illness bears directly on mens rea, for it suggests
Clark may not have known he was killing a human being.
It is striking that while the Court discusses at length the
likelihood of misjudgment from placing too much emphasis
on evidence of mental illness, see ante, at 773–778, it ignores
the risk of misjudging an innocent man guilty from refusing
to consider this highly relevant evidence at all. Clark’s ex
pert, it is true, said no one could know exactly what was on
Clark’s mind at the time of the shooting. See ante, at 777.
The expert testified extensively, however, about the effect of
Clark’s delusions on his perceptions of the world around him,
and about whether Clark’s behavior around the time of the
shooting was consistent with delusional thinking. This tes
timony was relevant to determining whether Clark knew he
was killing a human being. It also bolstered the testimony
of lay witnesses, none of which was deemed unreliable or
misleading by the state courts.
For the same reasons, the Court errs in seeking support
from the American Psychiatric Association’s statement that
a psychiatrist may be justifiably reluctant to reach legal con
clusions regarding the defendant’s mental state. See ante,
at 777–778. In this very case, the American Psychiatric As
sociation made clear that psychiatric evidence plays a crucial
role regardless of whether the psychiatrist testifies on the
ultimate issue: “Expert evidence of mental disorders, pre
sented by qualified professionals and subject to adversarial
testing, is both relevant to the mental-state issues raised by

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Kennedy, J., dissenting
mens rea requirements and reliable. . . . Such evidence could
not be condemned wholesale without unsettling the legal
system’s central reliance on such evidence.” Brief for
American Psychiatric Association et al. as Amici Curiae 15.
Contrary to the Court’s suggestion, see ante, at 776, the
fact that the state and defense experts drew different conclu
sions about the effect of Clark’s mental illness on his mental
state only made Clark’s evidence contested; it did not make
the evidence irrelevant or misleading. The trial court was
capable of evaluating the competing conclusions, as factfind
ers do in countless cases where there is a dispute among
witnesses. In fact, the potential to mislead will be far
greater under the Court’s new evidentiary system, where
jurors will receive observation evidence without the neces
sary explanation from experts.
The fact that mental-illness evidence may be considered in
deciding criminal responsibility does not compensate for its
exclusion from consideration on the mens rea elements of
the crime. Cf. ante, at 773–774. The evidence addresses
different issues in the two instances. Criminal responsibil
ity involves an inquiry into whether the defendant knew
right from wrong, not whether he had the mens rea elements
of the offense. While there may be overlap between the two
issues, “the existence or nonexistence of legal insanity bears
no necessary relationship to the existence or nonexistence of
the required mental elements of the crime.” Mullaney v.
Wilbur, 421 U. S. 684, 706 (1975) (Rehnquist, J., concurring).
Even if the analyses were equivalent, there is a different
burden of proof for insanity than there is for mens rea. Ari
zona requires the defendant to prove his insanity by clear
and convincing evidence. See Ariz. Rev. Stat. Ann. § 13–
502(C) (West 2001). The prosecution, however, must prove
all elements of the offense beyond a reasonable doubt. See
Mullaney, supra, at 703–704; In re Winship, 397 U. S. 358,
364 (1970). The shift in the burden on the criminal responsi
bility issue, while permissible under our precedent, see Le

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Kennedy, J., dissenting
land v. Oregon, 343 U. S. 790 (1952), cannot be applied to the
question of intent or knowledge without relieving the State
of its responsibility to establish this element of the offense.
See Sandstrom v. Montana, 442 U. S. 510, 524 (1979) ( jury
instruction that had the effect of placing the burden on the
defendant to disprove that he had the requisite mental state
violates due process). While evidentiary rules do not gener
ally shift the burden impermissibly, where there is a right
to have evidence considered on an element of the offense, the
right is not respected by allowing the evidence to come in
only on an issue for which the defendant bears the burden of
proof. See Cool v. United States, 409 U. S. 100, 103 (1972)
(per curiam) ( jury instruction that allowed jury to consider
accomplice’s testimony only if it was true beyond a reason
able doubt “places an improper burden on the defense and
allows the jury to convict despite its failure to find guilt be
yond a reasonable doubt”); Martin v. Ohio, 480 U. S. 228,
233–234 (1987) (State can shift the burden on a claim of self
defense, but if the jury were disallowed from considering
self-defense evidence for purposes of deciding the elements
of the offense, it “would relieve the State of its burden and
plainly run afoul of Winship’s mandate”). By viewing the
Arizona rule as creating merely a “presumption of sanity (or
capacity or responsibility),” ante, at 771, rather than a pre
sumption that the mens rea elements were not affected by
mental illness, the Court fails to appreciate the implications
for Winship.
The State attempts to sidestep the evidentiary issue en
tirely by claiming that its mental-illness exclusion simply al
ters one element of the crime. The evidentiary rule at issue
here, however, cannot be considered a valid redefinition of
the offense. Under the State’s logic, a person would be
guilty of first-degree murder if he knowingly or intentionally
killed a police officer or committed the killing under circum
stances that would show knowledge or intent but for the de
fendant’s mental illness. To begin with, Arizona law does

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not say this. And if it did, it would be impermissible.
States have substantial discretion in defining criminal of
fenses. In some instances they may provide that the ac
cused has the burden of persuasion with respect to affirma
tive defenses. See Patterson v. New York, 432 U. S. 197,
210 (1977). “But there are obviously constitutional limits
beyond which the States may not go in this regard.” Ibid.
If it were otherwise, States could label all evidentiary ex
clusions as redefinitions and so evade constitutional re
quirements. There is no rational basis, furthermore, for
criminally punishing a person who commits a killing without
knowledge or intent only if that person has a mental illness.
Cf. Robinson v. California, 370 U. S. 660, 666 (1962). The
State attempts to bring the instant case within the ambit
of Montana v. Egelhoff, 518 U. S. 37 (1996); but in Egelhoff
the excluded evidence concerned voluntary intoxication, for
which a person can be held responsible. Viewed either as
an evidentiary rule or a redefinition of the offense, it was
upheld because it “comports with and implements society’s
moral perception that one who has voluntarily impaired his
own faculties should be responsible for the consequences.”
Id., at 50 (plurality opinion). An involuntary mental illness
does not implicate this justification.
Future dangerousness is not, as the Court appears to con
clude, see ante, at 778–779, n. 45, a rational basis for convict
ing mentally ill individuals of crimes they did not commit.
Civil commitment proceedings can ensure that individuals
who present a danger to themselves or others receive proper
treatment without unfairly treating them as criminals. The
State presents no evidence to the contrary, and the Court
ought not to imply otherwise.
The State gains little support from Fisher v. United
States, 328 U. S. 463 (1946). There the defendant requested
an instruction from the trial court that the jury consider his
mental deficiencies in determining his capacity for premedi
tation and deliberation. Id., at 470. The Court noted that

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“[i]n view of the status of the defense of partial responsibility
in the District and the nation no contention is or could be
made of the denial of due process.” Id., at 466. This dic
tum may be attributable to the fact that the cases recogniz
ing a defendant’s evidentiary rights and the prosecution’s
duty to prove all elements beyond a reasonable doubt were
still decades away. It may also reflect the fact that the jury
instructions as given did seem to allow the jury to consider
evidence of mental deficiency if it disproved the elements of
the offense. See id., at 467, n. 3 (The jury instructions
stated, “ ‘It is further contended that even if sane and re
sponsible, there was no deliberate intent to kill, nor in fact
any actual intent to kill. Therefore if not guilty by reason
of insanity, the defendant at most is guilty only of second
degree murder or manslaughter’ ”). Even further ambigu
ity comes from the fact that the defense in Fisher concerned
a claim that the petitioner was “mentally somewhat below
the average” with a “psychopathic personality” of aggres
sion. Id., at 467. This general claim of mental deficiencies
was relevant to the “theory of partial responsibility,” id., at
470, he wanted the jury to consider. Unlike the mental ill
ness here, though, which concerns inadequacy of perception
and information processing, the petitioner’s claim may not
have been relevant to mens rea unless mens rea were rede
fined to include an element of responsibility. Fisher’s lan
guage, then, does not control this case.
While Arizona’s rule is not unique, either historically or in
contemporary practice, this fact does not dispose of Clark’s
constitutional argument. To the extent Fisher may have
suggested the contrary, subsequent cases make clear that
while the existence of the rule in some jurisdictions is a sig
nificant factor to consider, see Egelhoff, supra, at 43 (plural
ity opinion), it is not dispositive for evaluation of a claim that
the accused was foreclosed from introducing evidence crucial
to the defense. The evidentiary exclusion of accomplice tes
timony the Court invalidated in Washington was, in fact,

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well established. See 388 U. S., at 21–22. The exclusion of
hypnotically refreshed testimony likewise had some support
when the Court held it unconstitutional as applied to a
defendant’s own testimony. Rock, 483 U. S., at 57. While
13 States still impose significant restrictions on the use of
mental-illness evidence to negate mens rea, a substantial ma
jority of the States currently allow it. Brief for United
States as Amicus Curiae 22–23, and n. 13. The fact that a
reasonable number of States restrict this evidence weighs
into the analysis, but applying the rule as a per se bar, as
Arizona does, is so plainly unreasonable that it cannot be
sustained.
Putting aside the lack of any legitimate state interest for
application of the rule in this case, its irrationality is appar
ent when considering the evidence that is allowed. See
Washington, supra, at 22 (“The absurdity of the rule is
amply demonstrated by the exceptions that have been made
to it”). Arizona permits the defendant to introduce, for ex
ample, evidence of “behavioral tendencies” to show he did
not have the required mental state. See Mott, 187 Ariz., at
544, 931 P. 2d, at 1054; Christensen, 129 Ariz., at 35–36, 628
P. 2d, at 583–584. While defining mental illness is a difficult
matter, the State seems to exclude the evidence one would
think most reliable by allowing unexplained and uncatego
rized tendencies to be introduced while excluding relatively
well-understood psychiatric testimony regarding well
documented mental illnesses. It is unclear, moreover, what
would have happened in this case had the defendant wanted
to testify that he thought Officer Moritz was an alien. If
disallowed, it would be tantamount to barring Clark from
testifying on his behalf to explain his own actions. If al
lowed, then Arizona’s rule would simply prohibit the corrob
oration necessary to make sense of Clark’s explanation. In
sum, the rule forces the jury to decide guilt in a fictional
world with undefined and unexplained behaviors but without
mental illness. This rule has no rational justification and

548US2 Unit: $U87 [08-19-09 17:32:17] PAGES PGT: OPIN
801 Cite as: 548 U. S. 735 (2006)
Kennedy, J., dissenting
imposes a significant burden upon a straightforward defense:
He did not commit the crime with which he was charged.
These are the reasons for my respectful dissent.

Job: 548ORD Take: NOT1 Date/Time: 07-11-09 09:01:24
Reporter’s Note
The next page is purposely numbered 901. The numbers between 801
and 901 were intentionally omitted, in order to make it possible to publish
the orders with permanent page numbers, thus making the official cita
tions available upon publication of the preliminary prints of the United
States Reports.