Kahler v. Kansas

(Slip Opinion) OCTOBER TERM, 2019 1

Syllabus

NOTE: Where it is feasible, a syllabus (headnote) will be released, as is
being done in connection with this case, at the time the opinion is issued.
The syllabus constitutes no part of the opinion of the Court but has been
prepared by the Reporter of Decisions for the convenience of the reader.
See United States v. Detroit Timber & Lumber Co., 200 U. S. 321, 337.

SUPREME COURT OF THE UNITED STATES

Syllabus

KAHLER v. KANSAS

CERTIORARI TO THE SUPREME COURT OF KANSAS

No. 18–6135. Argued October 7, 2019—Decided March 23, 2020
In Clark v. Arizona, 548 U. S. 735, this Court catalogued the diverse
strains of the insanity defense that States have adopted to absolve
mentally ill defendants of criminal culpability. Two—the cognitive
and moral incapacity tests—appear as alternative pathways to acquit-
tal in the landmark English ruling M’Naghten’s Case, 10 Cl. & Fin.
200, 8 Eng. Rep. 718. The moral incapacity test asks whether a de-
fendant’s illness left him unable to distinguish right from wrong with
respect to his criminal conduct. Respondent Kansas has adopted the
cognitive incapacity test, which examines whether a defendant was
able to understand what he was doing when he committed a crime.
Specifically, under Kansas law a defendant may raise mental illness
to show that he “lacked the culpable mental state required as an ele-
ment of the offense charged,” Kan. Stat. Ann §21–5209. Kansas does
not recognize any additional way that mental illness can produce an
acquittal, although a defendant may use evidence of mental illness to
argue for a lessened punishment at sentencing. See §§21–
6815(c)(1)(C), 21–6625(a). In particular, Kansas does not recognize a
moral-incapacity defense.
Kansas charged petitioner James Kahler with capital murder after
he shot and killed four family members. Prior to trial, he argued that
Kansas’s insanity defense violates due process because it permits the
State to convict a defendant whose mental illness prevented him from
distinguishing right from wrong. The court disagreed and the jury re-
turned a conviction. During the penalty phase, Kahler was free to
raise any argument he wished that mental illness should mitigate his
sentence, but the jury still imposed the death penalty. The Kansas
Supreme Court rejected Kahler’s due process argument on appeal.
Held: Due process does not require Kansas to adopt an insanity test that
turns on a defendant’s ability to recognize that his crime was morally
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Syllabus

wrong. Pp. 6–24.
(a) A state rule about criminal liability violates due process only if it
“offends some principle of justice so rooted in the traditions and con-
science our people as to be ranked as fundamental.” Leland v. Oregon,
343 U. S. 790, 798 (internal quotation marks omitted). History is the
primary guide for this analysis. The due process standard sets a high
bar, and a rule of criminal responsibility is unlikely to be sufficiently
entrenched to bind all States to a single approach. As the Court ex-
plained in Powell v. Texas, 392 U. S. 514, the scope of criminal respon-
sibility is animated by complex and ever-changing ideas that are best
left to the States to evaluate and reevaluate over time. This principle
applies with particular force in the context of the insanity defense,
which also involves evolving understandings of mental illness. This
Court has thus twice declined to constitutionalize a particular version
of the insanity defense, see Leland, 343 U. S. 790; Clark, 548 U. S. 735,
holding instead that a State’s “insanity rule[ ] is substantially open to
state choice,” id., at 752. Pp. 6–9.
(b) Against this backdrop, Kahler argues that Kansas has abolished
the insanity defense—and, in particular, that it has impermissibly jet-
tisoned the moral-incapacity approach. As a starting point, Kahler is
correct that for hundreds of years jurists and judges have recognized
that insanity can relieve criminal responsibility. But Kansas recog-
nizes the same: Under Kansas law, mental illness is a defense to cul-
pability if it prevented a defendant from forming the requisite criminal
intent; a defendant is permitted to offer whatever evidence of mental
health he deems relevant at sentencing; and a judge has discretion to
replace a defendant’s prison term with commitment to a mental health
facility.
So Kahler can prevail only by showing that due process requires
States to adopt a specific test of insanity—namely, the moral-incapac-
ity test. He cannot do so. Taken as a whole, the early common law
cases and commentaries reveal no settled consensus favoring Kahler’s
preferred right-from-wrong rule. Even after M’Naghten gained popu-
larity in the 19th century, States continued to experiment with new
approaches. Clark therefore declared: “History shows no deference to
M’Naghten that could elevate its formula to the level of fundamental
principle.” 548 U. S., at 749–752. The tapestry of approaches States
have adopted shows that no single version of the insanity defense has
become so ingrained in American law as to rank as “fundamental.” Id.,
at 749.
This result is not surprising. Ibid. The insanity defense sits at the
juncture of medical views of mental illness and moral and legal theo-
ries of criminal culpability—two areas of conflict and change. Small
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Syllabus

wonder that no particular test of insanity has developed into a consti-
tutional baseline. And it is not for the courts to insist on any single
criterion moving forward. Defining the precise relationship between
criminal culpability and mental illness requires balancing complex
considerations, among them the workings of the brain, the purposes of
criminal law, and the ideas of free will and responsibility. This balance
should remain open to revision as new medical knowledge emerges and
societal norms evolve. Thus—as the Court recognized previously in
Leland, Powell, and Clark—the defense is a project for state govern-
ance, not constitutional law. Pp. 10–24.
307 Kan. 374, 410 P. 3d 105, affirmed.

KAGAN, J., delivered the opinion of the Court, in which ROBERTS, C. J.,
and THOMAS, ALITO, GORSUCH, and KAVANAUGH, JJ., joined. BREYER, J.,
filed a dissenting opinion, in which GINSBURG and SOTOMAYOR, JJ.,
joined.
 Cite as: 589 U. S. ____ (2020) 1

Opinion of the Court

NOTICE: This opinion is subject to formal revision before publication in the
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notify the Reporter of Decisions, Supreme Court of the United States, Wash-
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corrections may be made before the preliminary print goes to press.

SUPREME COURT OF THE UNITED STATES
_________________

No. 18–6135
_________________

JAMES K. KAHLER, PETITIONER v. KANSAS
ON WRIT OF CERTIORARI TO THE SUPREME COURT OF KANSAS
[March 23, 2020]

JUSTICE KAGAN delivered the opinion of the Court.
This case is about Kansas’s treatment of a criminal de-
fendant’s insanity claim. In Kansas, a defendant can in-
voke mental illness to show that he lacked the requisite
mens rea (intent) for a crime. He can also raise mental ill-
ness after conviction to justify either a reduced term of im-
prisonment or commitment to a mental health facility. But
Kansas, unlike many States, will not wholly exonerate a de-
fendant on the ground that his illness prevented him from
recognizing his criminal act as morally wrong. The issue
here is whether the Constitution’s Due Process Clause
forces Kansas to do so—otherwise said, whether that
Clause compels the acquittal of any defendant who, because
of mental illness, could not tell right from wrong when com-
mitting his crime. We hold that the Clause imposes no such
requirement.
I
A
In Clark v. Arizona, 548 U. S. 735, 749 (2006), this Court
catalogued state insanity defenses, counting four “strains
variously combined to yield a diversity of American stand-
ards” for when to absolve mentally ill defendants of crimi-
nal culpability. The first strain asks about a defendant’s
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Opinion of the Court

“cognitive capacity”—whether a mental illness left him “un-
able to understand what he [was] doing” when he commit-
ted a crime. Id., at 747, 749. The second examines his
“moral capacity”—whether his illness rendered him “un-
able to understand that his action [was] wrong.” Ibid. Those
two inquiries, Clark explained, appeared as alternative
pathways to acquittal in the landmark English ruling
M’Naghten’s Case, 10 Cl. & Fin. 200, 8 Eng. Rep. 718 (H. L.
1843), as well as in many follow-on American decisions and
statutes: If the defendant lacks either cognitive or moral ca-
pacity, he is not criminally responsible for his behavior. Yet
a third “building block[ ]” of state insanity tests, gaining
popularity from the mid-19th century on, focuses on “voli-
tional incapacity”—whether a defendant’s mental illness
made him subject to “irresistible[] impulse[s]” or otherwise
unable to “control[ ] his actions.” Clark, 548 U. S., at 749,
750, n. 11; see, e.g., Parsons v. State, 81 Ala. 577, 597, 2 So.
854, 866–867 (1887). And bringing up the rear, in Clark’s
narration, the “product-of-mental-illness test” broadly con-
siders whether the defendant’s criminal act stemmed from
a mental disease. 548 U. S., at 749–750.
As Clark explained, even that taxonomy fails to capture
the field’s complexity. See id., at 750, n. 11. Most notable
here, M’Naghten’s “moral capacity” prong later produced a
spinoff, adopted in many States, that does not refer to mo-
rality at all. Instead of examining whether a mentally ill
defendant could grasp that his act was immoral, some ju-
risdictions took to asking whether the defendant could un-
derstand that his act was illegal. Compare, e.g., People v.
Schmidt, 216 N. Y. 324, 333–334, 110 N. E. 945, 947 (1915)
(Cardozo, J.) (asking about moral right and wrong), with,
e.g., State v. Hamann, 285 N. W. 2d 180, 183 (Iowa 1979)
(substituting ideas of legal right and wrong). That change
in legal standard matters when a mentally ill defendant
knew that his act violated the law yet believed it morally
justified. See, e.g., Schmidt, 216 N. Y., at 339, 110 N. E., at
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Opinion of the Court

949; People v. Serravo, 823 P. 2d 128, 135 (Colo. 1992).1
Kansas law provides that “[i]t shall be a defense to a pros-
ecution under any statute that the defendant, as a result of
mental disease or defect, lacked the culpable mental state
required as an element of the offense charged.” Kan. Stat.
Ann. §21–5209 (2018 Cum. Supp.).2 Under that statute, a
defendant may introduce any evidence of any mental illness
to show that he did not have the intent needed to commit
the charged crime. Suppose, for example, that the defend-
ant shot someone dead and goes on trial for murder. He
may then offer psychiatric testimony that he did not under-
stand the function of a gun or the consequences of its use—
more generally stated, “the nature and quality” of his ac-
tions. M’Naghten, 10 Cl. & Fin., at 210, 8 Eng. Rep., at 722.
And a jury crediting that testimony must acquit him. As
everyone here agrees, Kansas law thus uses M’Naghten’s
“cognitive capacity” prong—the inquiry into whether a
mentally ill defendant could comprehend what he was do-
ing when he committed a crime. See Brief for Petitioner 41;
Brief for Respondent 31; Brief for United States as Amicus
Curiae 18. If the defendant had no such capacity, he could
not form the requisite intent—and thus is not criminally
responsible.
At the same time, the Kansas statute provides that
“[m]ental disease or defect is not otherwise a defense.” §21–
5209. In other words, Kansas does not recognize any addi-
tional way that mental illness can produce an acquittal.3
——————
1 Another complicating factor in Clark’s classification scheme is that

States “limit, in varying degrees, which sorts of mental illness” can sup-
port an insanity claim. Clark v. Arizona, 548 U. S. 735, 750, n. 11 (2006).
So even two States using the same test for judging culpability may apply
it to differently sized sets of offenders. See infra, at 21, n. 11.
2 At the time of the crime in this case, a materially identical provision

was codified at §22–3220 (2007).
3 Four other States similarly exonerate a mentally ill defendant only

when he cannot understand the nature of his actions and so cannot form
the requisite mens rea. See Alaska Stat. §§12.47.010(a), 12.47.020
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Opinion of the Court

Most important for this case, a defendant’s moral incapac-
ity cannot exonerate him, as it would if Kansas had adopted
both original prongs of M’Naghten. Assume, for example,
that a defendant killed someone because of an “insane de-
lusion that God ha[d] ordained the sacrifice.” Schmidt, 216
N. Y., at 339, 110 N. E., at 949. The defendant knew what
he was doing (killing another person), but he could not tell
moral right from wrong; indeed, he thought the murder
morally justified. In many States, that fact would preclude
a criminal conviction, although it would almost always lead
to commitment in a mental health facility. In Kansas, by
contrast, evidence of a mentally ill defendant’s moral inca-
pacity—or indeed, of anything except his cognitive inability
to form the needed mens rea—can play no role in determin-
ing guilt.
That partly closed-door policy changes once a verdict is
in. At the sentencing phase, a Kansas defendant has wide
latitude to raise his mental illness as a reason to judge him
not fully culpable and so to lessen his punishment. See
§§21–6815(c)(1)(C), 21–6625(a). He may present evidence
(of the kind M’Naghten deemed relevant) that his dis-
ease made him unable to understand his act’s moral wrong-
ness—as in the example just given of religious delusion.
See §21–6625(a). Or he may try to show (in line with
M’Naghten’s spinoff ) that the illness prevented him
from “appreciat[ing] the [conduct’s] criminality.” §21–
6625(a)(6). Or again, he may offer testimony (here invoking
volitional incapacity) that he simply could not “conform
[his] conduct” to legal restraints. Ibid. Kansas sentencing
law thus provides for an individualized determination of
how mental illness, in any or all of its aspects, affects cul-
pability. And the same kind of evidence can persuade a
court to place a defendant who needs psychiatric care in a
——————
(2018); Idaho Code Ann. §§18–207(1), (3) (2016); Mont. Code Ann. §46–
14–102 (2019); Utah Code §76–2–305 (2017).
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Opinion of the Court

mental health facility rather than a prison. See §22–3430.
In that way, a defendant in Kansas lacking, say, moral ca-
pacity may wind up in the same kind of institution as a like
defendant in a State that would bar his conviction.
B
This case arises from a terrible crime. In early 2009, Ka-
ren Kahler filed for divorce from James Kahler and moved
out of their home with their two teenage daughters and
9-year-old son. Over the following months, James Kahler
became more and more distraught. On Thanksgiving week-
end, he drove to the home of Karen’s grandmother, where
he knew his family was staying. Kahler entered through
the back door and saw Karen and his son. He shot Karen
twice, while allowing his son to flee the house. He then
moved through the residence, shooting Karen’s grand-
mother and each of his daughters in turn. All four of his
victims died. Kahler surrendered to the police the next day
and was charged with capital murder.
Before trial, Kahler filed a motion arguing that Kansas’s
treatment of insanity claims violates the Fourteenth
Amendment’s Due Process Clause. Kansas, he asserted,
had “unconstitutionally abolished the insanity defense” by
allowing the conviction of a mentally ill person “who cannot
tell the difference between right and wrong.” App. 11–12.
The trial court denied the motion, leaving Kahler to at-
tempt to show through psychiatric and other testimony that
severe depression had prevented him from forming the in-
tent to kill. See id., at 16; §21–5209. The jury convicted
Kahler of capital murder. At the penalty phase, the court
permitted Kahler to offer additional evidence of his mental
illness and to argue in whatever way he liked that it should
mitigate his sentence. The jury still decided to impose the
death penalty.
Kahler appealed, again challenging the constitutionality
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Opinion of the Court

of Kansas’s approach to insanity claims. The Kansas Su-
preme Court rejected his argument, relying on an earlier
precedential decision. See 307 Kan. 374, 400–401, 410
P. 3d 105, 124–125 (2018) (discussing State v. Bethel, 275
Kan. 456, 66 P. 3d 840 (2003)). There, the court denied that
any single version of the insanity defense is so “ingrained
in our legal system” as to count as “fundamental.” Id., at
473, 66 P. 3d, at 851. The court thus found that “[d]ue pro-
cess does not mandate that a State adopt a particular in-
sanity test.” Ibid.
Kahler then asked this Court to decide whether the Due
Process Clause requires States to provide an insanity de-
fense that acquits a defendant who could not “distinguish
right from wrong” when committing his crime—or, other-
wise put, whether that Clause requires States to adopt the
moral-incapacity test from M’Naghten. Pet. for Cert. 18.
We granted certiorari, 586 U. S. ___ (2019), and now hold it
does not.4
II
A
A challenge like Kahler’s must surmount a high bar. Un-
der well-settled precedent, a state rule about criminal lia-
bility—laying out either the elements of or the defenses to
a crime—violates due process only if it “offends some prin-
ciple of justice so rooted in the traditions and conscience of
our people as to be ranked as fundamental.” Leland v. Or-
egon, 343 U. S. 790, 798 (1952) (internal quotation marks
omitted). Our primary guide in applying that standard is
“historical practice.” Montana v. Egelhoff, 518 U. S. 37, 43
(1996) (plurality opinion). And in assessing that practice,
——————
4 Kahler also asked us to decide whether the Eighth Amendment re-

quires that States make available the moral-incapacity defense. See Pet.
for Cert. 18. But that claim is not properly before us. Kahler did not
raise the argument below, and the Kansas courts therefore did not ad-
dress it.
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Opinion of the Court

we look primarily to eminent common-law authorities
(Blackstone, Coke, Hale, and the like), as well as to early
English and American judicial decisions. See, e.g., id., at
44–45; Patterson v. New York, 432 U. S. 197, 202 (1977).
The question is whether a rule of criminal responsibility is
so old and venerable—so entrenched in the central values
of our legal system—as to prevent a State from ever choos-
ing another. An affirmative answer, though not unheard
of, is rare. See, e.g., Clark, 548 U. S., at 752 (“[T]he concep-
tualization of criminal offenses” is mostly left to the States).
In Powell v. Texas, 392 U. S. 514 (1968), this Court ex-
plained why. There, Texas declined to recognize “chronic
alcoholism” as a defense to the crime of public drunkenness.
Id., at 517 (plurality opinion). The Court upheld that deci-
sion, emphasizing the paramount role of the States in set-
ting “standards of criminal responsibility.” Id., at 533. In
refusing to impose “a constitutional doctrine” defining those
standards, the Court invoked the many “interlocking and
overlapping concepts” that the law uses to assess when a
person should be held criminally accountable for “his anti-
social deeds.” Id., at 535–536. “The doctrines of actus reus,
mens rea, insanity, mistake, justification, and duress”—the
Court counted them off—reflect both the “evolving aims of
the criminal law” and the “changing religious, moral, phil-
osophical, and medical views of the nature of man.” Id., at
536. Or said a bit differently, crafting those doctrines in-
volves balancing and rebalancing over time complex and
oft-competing ideas about “social policy” and “moral culpa-
bility”—about the criminal law’s “practical effectiveness”
and its “ethical foundations.” Id., at 538, 545, 548 (Black,
J., concurring). That “constantly shifting adjustment”
could not proceed in the face of rigid “[c]onstitution[al] for-
mulas.” Id., at 536–537 (plurality opinion). Within broad
limits, Powell thus concluded, “doctrine[s] of criminal re-
sponsibility” must remain “the province of the States.” Id.,
at 534, 536.
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Opinion of the Court

Nowhere has the Court hewed more closely to that view
than in addressing the contours of the insanity defense.
Here, uncertainties about the human mind loom large. See,
e.g., Ake v. Oklahoma, 470 U. S. 68, 81 (1985) (“[P]sychia-
trists disagree widely and frequently on what constitutes
mental illness, on [proper] diagnos[es, and] on cure and
treatment”). Even as some puzzles get resolved, others
emerge. And those perennial gaps in knowledge intersect
with differing opinions about how far, and in what ways,
mental illness should excuse criminal conduct. See Clark,
548 U. S., at 749–752 (canvassing how those competing
views produced a wealth of insanity tests); supra, at 1–2.
“This whole problem,” we have noted, “has evoked wide dis-
agreement.” Leland, 343 U. S., at 801. On such unsettled
ground, we have hesitated to reduce “experimentation, and
freeze [the] dialogue between law and psychiatry into a
rigid constitutional mold.” Powell, 392 U. S., at 536–537.
Indeed, while addressing the demand for an alcoholism de-
fense in Powell, the Court pronounced—as something close
to self-evident—that “[n]othing could be less fruitful” than
to define a specific “insanity test in constitutional terms.”
Id., at 536.
And twice before we have declined to do so. In Leland v.
Oregon, a criminal defendant challenged as a violation of due
process the State’s use of the moral-incapacity test of insan-
ity—the very test Kahler now asks us to require. See 343
U. S., at 800–801. According to the defendant, Oregon in-
stead had to adopt the volitional-incapacity (or irresistible-
impulse) test to comply with the Constitution. See ibid.;
supra, at 2. We rejected that argument. “[P]sychiatry,” we
first noted, “has made tremendous strides since [the moral-
incapacity] test was laid down in M’Naghten’s Case,” imply-
ing that the test seemed a tad outdated. 343 U. S., at 800–
801. But still, we reasoned, “the progress of science has not
reached a point where its learning” would demand “elimi-
nat[ing] the right and wrong test from [the] criminal law.”
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Opinion of the Court

Id., at 801. And anyway, we continued, the “choice of a test
of legal sanity involves not only scientific knowledge but
questions of basic policy” about when mental illness should
absolve someone of “criminal responsibility.” Ibid. The
matter was thus best left to each State to decide on its own.
The dissent agreed (while parting from the majority on an-
other ground): “[I]t would be indefensible to impose upon
the States[ ] one test rather than another for determining
criminal culpability” for the mentally ill, “and thereby to
displace a State’s own choice.” Id., at 803 (opinion of Frank-
furter, J.).
A half-century later, we reasoned similarly in Clark.
There, the defendant objected to Arizona’s decision to dis-
card the cognitive-incapacity prong of M’Naghten and leave
in place only the moral-incapacity one—essentially the flip-
side of what Kansas has done. Again, we saw no due pro-
cess problem. Many States, we acknowledged, allowed a
defendant to show insanity through either prong of
M’Naghten. See 548 U. S., at 750. But we denied that this
approach “represents the minimum that a government
must provide.” Id., at 748. In so doing, we invoked the
States’ traditional “capacity to define crimes and defenses,”
and noted how views of mental illness had been particularly
“subject to flux and disagreement.” Id., at 749, 752. And
then we surveyed the disparate ways that state laws had
historically excused criminal conduct because of mental dis-
ease—those “strains variously combined to yield a diversity
of American standards.” See id., at 749–752; supra, at 1–2.
The takeaway was “clear”: A State’s “insanity rule[ ] is sub-
stantially open to state choice.” Clark, 548 U. S., at 752.
Reiterating Powell’s statement, Clark held that “no partic-
ular” insanity test serves as “a baseline for due process.”
548 U. S., at 752. Or said just a bit differently, that “due
process imposes no single canonical formulation of legal in-
sanity.” Id., at 753.
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Opinion of the Court

B
Yet Kahler maintains that Kansas’s treatment of insan-
ity fails to satisfy due process. He sometimes makes his
argument in the broadest of strokes, as he did before trial.
See supra, at 5. Kansas, he then contends, has altogether
“abolished the insanity defense,” in disregard of hundreds
of years of historical practice. Brief for Petitioner 39. His
central claim, though, is more confined. It is that Kansas
has impermissibly jettisoned the moral-incapacity test for
insanity. See id., at 12, 23. As earlier noted, both Clark
and Leland described that test as coming from M’Naghten.
See 548 U. S., at 749; 343 U. S., at 801; supra, at 2, 8. But
according to Kahler (and the dissent), the moral-incapacity
inquiry emerged centuries before that decision, thus form-
ing part of the English common-law heritage this country
inherited. See Brief for Petitioner 21, 42; post, at 4–14
(opinion of BREYER, J.). And the test, he claims, served for
all that time—and continuing into the present—as the
touchstone of legal insanity: If a defendant could not under-
stand that his act was morally wrong, then he could not be
found criminally liable. See Brief for Petitioner 20–23;
see also post, at 15. So Kahler concludes that the moral-
incapacity standard is a “principle of justice so rooted in the
traditions and conscience of our people as to be ranked as
fundamental.” Leland, 343 U. S., at 798; see supra, at 6. In
essence—and contra Clark—that test is the “single canoni-
cal formulation of legal insanity” and thus the irreducible
“baseline for due process.” 548 U. S., at 752–753; see supra,
at 9.5
——————
5 Although the dissent at times claims to the contrary, its argument is

the same. Given the clear direction of our precedent, the dissent must
purport to grant the States “leeway” in defining legal insanity. Post, at
1. But the entirety of the dissent’s historical analysis focuses on the
moral-incapacity standard—attempting to show, just as Kahler does,
that it both preceded and succeeded M’Naghten. See post, at 4–17. And
in line with that narration, the dissent insists on moral understanding
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Opinion of the Court

One point, first, of agreement: Kahler is right that for
hundreds of years jurists and judges have recognized insan-
ity (however defined) as relieving responsibility for a crime.
“In criminal cases therefore,” Sir William Blackstone wrote,
“lunatics are not chargeable for their own acts, if committed
when under these incapacities.” 4 Commentaries on the
Laws of England 24 (1769). Sir Edward Coke even earlier
explained that in criminal cases, “the act and wrong of a
mad man shall not be imputed to him.” 2 Institutes of the
Laws of England §405, p. 247b (1628) (Coke). And so too
Henry de Bracton thought that a “madman” could no sooner
be found criminally liable than a child. 2 Bracton on Laws
and Customs of England 384 (S. Thorne transl. 1968) (Brac-
ton). That principle of non-culpability appeared in case af-
ter case involving allegedly insane defendants, on both
sides of the Atlantic. “The defense of insanity[] is a defense
for all crimes[,] from the highest to the lowest,” said the
Court in Old Bailey. Trial of Samuel Burt (July 19, 1786),
in 6 Proceedings in the Old Bailey 874 (E. Hodgson ed.
1788) (Old Bailey Proceedings). Repeated Justice Story,
when riding circuit: “In general, insanity is an excuse for
the commission of every crime, because the party has not
the possession of that reason, which includes responsibil-
ity.” United States v. Drew, 25 F. Cas. 913 (No. 14,993) (CC
Mass. 1828); see also, e.g., State v. Marler, 2 Ala. 43, 49
(1841) (“If the prisoner was insane, he was not an account-
able being”); Cornwell v. State, 8 Tenn. 147, 156 (1827)
(“[P]erfect madness” will “free a man from punishment for
crime”). We have not found a single case to the contrary.
——————
as the indispensable criterion of legal sanity—the sine qua non of crimi-
nal responsibility. See, e.g., post, at 1, 3–4, 8–9, 18–21. Indeed, the dis-
sent offers only one way the States have actual “leeway” to change their
insanity rules: They can “expand upon M’Naghten’s principles” by find-
ing that even some who have moral capacity are insane. Post, at 22. But
that is just to say that moral capacity is the constitutional floor—again,
exactly what Kahler argues.
12 KAHLER v. KANSAS

Opinion of the Court

But neither do we think Kansas departs from that broad
principle. First, Kansas has an insanity defense negating
criminal liability—even though not the type Kahler de-
mands. As noted earlier, Kansas law provides that it is “a
defense to a prosecution” that “the defendant, as a result of
mental disease or defect, lacked the culpable mental state
required” for a crime. §21–5209; see supra, at 3. That pro-
vision enables a defendant to present psychiatric and other
evidence of mental illness to defend himself against a crim-
inal charge. More specifically, the defendant can use that
evidence to show that his illness left him without the cogni-
tive capacity to form the requisite intent. See supra, at 3.
Recall that such a defense was exactly what the defendant
in Clark wanted, in preference to Arizona’s moral-incapacity
defense: His (unsuccessful) appeal rested on the trial court’s
exclusion of psychiatric testimony to show that he lacked
the relevant mens rea. See 548 U. S., at 745–747; supra, at
9. Here, Kahler could do what Clark could not—try to show
through such testimony that he had no intent to kill. Of
course, Kahler would have preferred Arizona’s kind of in-
sanity defense (just as Clark would have liked Kansas’s).
But that does not mean that Kansas (any more than Ari-
zona) failed to offer any insanity defense at all.
Second, and significantly, Kansas permits a defendant to
offer whatever mental health evidence he deems relevant
at sentencing. See §§21–6815(c)(1)(C), 21–6625(a); supra,
at 4. A mentally ill defendant may argue there that he is
not blameworthy because he could not tell the difference be-
tween right and wrong. Or, because he did not know his
conduct broke the law. Or, because he could not control his
behavior. Or, because of anything else. In other words, any
manifestation of mental illness that Kansas’s guilt-phase
insanity defense disregards—including the moral incapac-
ity Kahler highlights—can come in later to mitigate culpa-
bility and lessen punishment. And that same kind of evi-
dence can persuade a judge to replace any prison term with
 Cite as: 589 U. S. ____ (2020) 13

Opinion of the Court

commitment to a mental health facility. See §22–3430; su-
pra, at 4–5. So as noted above, a defendant arguing moral
incapacity may well receive the same treatment in Kansas
as in States that would acquit—and, almost certainly, com-
mit—him for that reason. See supra, at 4–5. In sum, Kan-
sas does not bar, but only channels to sentencing, the men-
tal health evidence that falls outside its intent-based
insanity defense. When combined with Kansas’s allowance
of mental health evidence to show a defendant’s inability to
form criminal intent, that sentencing regime defeats
Kahler’s charge that the State has “abolish[ed] the insanity
defense entirely.”6 Brief for Petitioner 39.
So Kahler can prevail here only if he can show (again,
contra Clark) that due process demands a specific test of
legal insanity—namely, whether mental illness prevented
a defendant from understanding his act as immoral. Kan-
sas, as we have explained, does not use that type of insanity
rule. See supra, at 3–4. If a mentally ill defendant had
enough cognitive function to form the intent to kill, Kansas
law directs a conviction even if he believed the murder mor-
ally justified. In Kansas’s judgment, that delusion does not
make an intentional killer entirely blameless. See Brief for
Respondent 40. Rather than eliminate, it only lessens the
defendant’s moral culpability. See ibid. And sentencing is
the appropriate place to consider mitigation: The deci-
sionmaker there can make a nuanced evaluation of blame,
rather than choose, as a trial jury must, between all and
nothing. See ibid. In any event, so Kansas thinks.7 Those
——————
6 We here conclude only that Kansas’s scheme does not abolish the in-

sanity defense. We say nothing, one way or the other, about whether any
other scheme might do so.
7 The dissent is therefore wrong to suggest that Kansas’s law has be-

come untethered from moral judgments about culpability. See post, at 1,
3, 16–22. No doubt, Kansas’s moral judgments differ from the dissent’s.
Again, Kansas believes that an intentional killer is not wholly blameless,
even if, for example, he thought his actions commanded by God. The
dissent, in contrast, considers Kansas’s view benighted (as maybe some
14 KAHLER v. KANSAS

Opinion of the Court

views are contested and contestable; other States—many
others—have made a different choice. But Kahler must
show more than that. He must show that adopting the
moral-incapacity version of the insanity rule is not a choice
at all—because, again, that version is “so rooted in the
traditions and conscience of our people as to be ranked as
fundamental.” Leland, 343 U. S., at 798. And he cannot.
The historical record is, on any fair reading, complex—even
messy. As we will detail, it reveals early versions of
not only Kahler’s proposed standard but also Kansas’s
alternative.
Early commentators on the common law proposed vari-
ous formulations of the insanity defense, with some favor-
ing a morality inquiry and others a mens rea approach.
Kahler cites William Lambard’s 16th-century treatise de-
fining a “mad man” as one who “hath no knowledge of good
nor evil” (the right and wrong of the day). Eirenarcha, ch.
21, p. 218 (1581). He likewise points to William Hawkins’s
statement, over a hundred years later, that a “lunatick[ ]” is
not punishable because “under a natural disability of dis-
tinguishing between good and evil.” 1 Pleas of the Crown
§1, p. 2 (1716) (capitalization omitted). Both true enough.
But other early versions of the insanity test—and from a
more famous trio of jurists—demanded the kind of cognitive

——————
in the majority do too). But that is not a dispute, as the dissent suggests,
about whether morality should play a role in assigning legal responsibil-
ity. It is instead a disagreement about what morality entails—that is,
about when a defendant is morally culpable for an act like murder. See
State v. Bethel, 275 Kan. 456, 465–471, 66 P. 3d 840, 847–850 (2003) (ac-
cepting Kansas’s view that “moral blameworthiness” is linked to a de-
fendant’s intent to kill, rather than to his ability to tell right from wrong).
And we have made clear, from Leland to Powell to Clark, that courts do
not get to make such judgments. See supra, at 7–9. Instead, the States
have broad discretion to decide who counts as blameworthy, and to weigh
that along with other factors in defining the elements of, and defenses
to, crimes.
 Cite as: 589 U. S. ____ (2020) 15

Opinion of the Court

impairment that prevented a defendant from understand-
ing the nature of his acts, and thus intending his crime.
Henry de Bracton’s 13th-century treatise gave rise to what
became known as the “wild beast” test. See J. Biggs, The
Guilty Mind 82 (1955). Used for hundreds of years, it lik-
ened a “madman” to an “animal[ ] which lack[s] reason” and
so could not have “the intention to injure.” Bracton 384; see
ibid. (A “madman” cannot commit a crime because “[i]t is
will and purpose which mark” misdeeds). Sir Edward Coke
similarly linked the definition of insanity to a defendant’s
inability to form criminal intent. He described a legally in-
sane person in 1628 as so utterly “without his mind or dis-
cretion” that he could not have the needed mens rea. 2 Coke
§405, at 247b. So too Lord Matthew Hale a century later.
He explained that insanity involves “a total alienation of
the mind or perfect madness,” such that a defendant could
not act “animo felonico,” meaning with felonious intent. 1
Pleas of the Crown, ch. 4, pp. 30, 37 (1736); see id., at 37
(“[F]or being under a full alienation of mind, he acts not per
electionem or intentionem [by choice or intent]”).8
——————
8 The dissent tries to recruit these three jurists to the side of the moral-

incapacity test, see post, at 5–7, but cannot succeed. Even the carefully
curated passages the dissent quotes focus on cognitive capability rather
than moral judgment. See, e.g., post, at 5–6 (asking whether a defendant
had “sense and reason” or “understanding and liberty of will”). In so
doing, they refer to the defendant’s ability to form the requisite mens rea,
or felonious intent. See Clark, 548 U. S., at 747; supra, at 1–3.
The dissent still insists all is not lost because (it says) mens rea itself
hinged at common law on a defendant’s “moral understanding.” Post, at
8–9. Here, the dissent infers from the use of “good-from-evil” language
in various common-law treatises and cases that moral blameworthiness
must have defined the mens rea inquiry. See ibid. But to begin with—
and to repeat the point made in the text—the most influential treatises
used little of that language, emphasizing instead the need for a defend-
ant to intend his act in the ordinary sense of the term. And as we will
explain, the joint presence of references to mens rea and moral under-
standing in other common-law sources involving insanity does not show
that most jurists saw the two concepts as one and the same. See infra,
16 KAHLER v. KANSAS

Opinion of the Court

Quite a few of the old common-law cases similarly
stressed the issue of cognitive capacity. To be sure, even
these cases included some references to the ability to tell
right from wrong (and the dissent eagerly cherry-picks
every one of them). But the decisions’ overall focus was less
on whether a defendant thought his act moral than on
whether he had the ability to do much thinking at all. In
the canonical case of Rex v. Arnold, 16 How. St. Tr. 695
(1724), for example, the jury charge descended straight
from Bracton:
“[I]t is not every kind of frantic humour or something
unaccountable in a man’s actions, that points him out
to be such a madman as is to be exempted from punish-
ment: it must be a man that is totally deprived of his
understanding and memory, and doth not know what
he is doing, no more than an infant, than a brute, or a
wild beast.” Id., at 764–765.
And the court offered an accompanying test linking that
lack of reason to mens rea: If a man is “deprived of his rea-
son, and consequently of his intention, he cannot be guilty.”
Id., at 764; see ibid. (defining a “madman” as a “person that
hath no design”); see also Trial of William Walker (Apr. 21,
1784), in 4 Old Bailey Proceedings 544, 547 (asking whether
the defendant had a “distemper of mind which had deprived
him of the use of his reason” or instead whether “he knew
what he was doing [and] meant to do it”); Beverley’s Case, 4
Co. Rep. 123b, 124b, 76 Eng. Rep. 1118, 1121 (K. B. 1603)

——————
at 16–19. Some may well have viewed mens rea through a moral prism;
but others emphasized cognitive understanding in using that term; and
still others combined the moral and cognitive in diverse ways. Which is
to say that the record is far more complicated than the dissent lets on,
with jurists invoking, both within particular sources and across all of
them, a variety of ways to resolve insanity claims. And under our long-
established precedent, that motley sort of history cannot provide the ba-
sis for a successful due process claim.
 Cite as: 589 U. S. ____ (2020) 17

Opinion of the Court

(asking whether a man “is deprived of reason and under-
standing” and so “cannot have a felonious intent”). The
House of Lords used much the same standard in Rex v. Lord
Ferrers, 19 How. St. Tr. 886 (1760), when sitting in judg-
ment on one of its members. There, the Solicitor General
told the Lords to address “the capacity and intention of the
noble prisoner.” Id., at 948. Relying heavily on Hale’s trea-
tise, he defined the legally insane as suffering from an “al-
ienation of mind” and a “total[ ] want of reason.” Id., at 947.
And in recapping the evidence on that issue, he asked about
the defendant’s intention: “Did [Ferrers] proceed with de-
liberation? Did he know the consequences” of his act? Id.,
at 948.9
In such cases, even the language of morality mostly
worked in service of the emphasis on cognition and mens
rea. The idea was that if a defendant had such a “total[]
want of reason” as to preclude moral thinking, he could not
possibly have formed the needed criminal intent. Id., at
947. Lord Chief Justice Mansfield put the point neatly in
Bellingham’s Case, 1 G. Collinson, Treatise on the Law Con-
cerning Idiots, Lunatics, and Other Persons Non Compotes
——————
9 Even in the face of these instructions, the dissent claims that Arnold

and Ferrers actually used the moral-incapacity test. See post, at 9–11.
The assertion is based on some “good and evil” language (in Ferrers,
mostly from witnesses) appearing in the case reports. But scholars gen-
erally agree, in line with our view, that Arnold and Ferrers “demonstrate
how strictly” courts viewed “the criteria of insanity.” 1 N. Walker, Crime
and Insanity in England 53 (1968) (noting that the two decisions “have
often been cited” for that proposition). Kahler himself does not dispute
the point; indeed, he essentially concedes our reading. Rather than try
to make the decisions say something they do not, he argues only that
they were “outlier[s]” and “could hardly have been less typical.” Brief for
Petitioner 22, n. 5; Reply Brief 4 (internal quotation marks omitted). But
that contrasting response fares no better. As even the dissent agrees,
these were the “seminal” common-law decisions relating to insanity—in-
deed, two of only a small number in that period to make it into official
reports. Post, at 9.
18 KAHLER v. KANSAS

Opinion of the Court

Mentis 636 (1812) (Collinson). He instructed the jury:
“If a man were deprived of all power of reasoning, so as
not to be able to distinguish whether it was right or
wrong to commit the most wicked transaction, he could
not certainly do an act against the law. Such a man, so
destitute of all power of judgment, could have no inten-
tion at all.” Id., at 671.
On that account, moral incapacity was a byproduct of the
kind of cognitive breakdown that precluded finding mens
rea, rather than a self-sufficient test of insanity. See also
Rex v. Offord, 5 Car. & P. 168, 169, 172 Eng. Rep. 924, 925
(N. P. 1831) (“express[ing] complete accordance in the ob-
servations of th[e] learned Judge” in Bellingham). Or said
another way, a mentally ill defendant’s inability to distin-
guish right from wrong, rather than independently produc-
ing an insanity acquittal, served as a sign—almost a kind
of evidence—that the defendant lacked the needed criminal
intent.
Other early common-law cases do not adopt the mens rea
approach—but neither can they sustain Kahler’s position.
Kahler relies mainly on Hadfield’s Case, 27 How. St. Tr.
1281 (1800), to show that common-law courts would acquit
a mentally ill defendant who understood the nature of his
act, but believed it moral. See Reply Brief 4. There, the
defendant had deliberately set out to assassinate King
George III on the view that doing so would bring about the
Second Coming. See 27 How. St. Tr., at 1322. The judge
instructed the jury that the defendant was so “deranged” as
to make acquittal appropriate. Id., at 1353. Maybe, as
Kahler argues, that directive stemmed from the defendant’s
inability to tell right from wrong. But the judge never used
that language, or stated any particular legal standard, so it
is hard to know. Still other judges explained insanity to
juries by throwing everything against the wall—mixing no-
tions of cognitive incapacity, moral incapacity, and more,
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Opinion of the Court

without trying to order, prioritize, or even distinguish
among them. See, e.g., Regina v. Oxford, 9 Car. & P. 525,
545–548, 173 Eng. Rep. 941, 950 (N. P. 1840); Trial of Fran-
cis Parr (Jan. 15, 1787), in 2 Old Bailey Proceedings 228–
229; Bowler’s Case, 1 Collinson 674. Those decisions treat
the inability to make moral judgments more as part of an
all-things-considered assessment of legal insanity, and less
as its very definition. But even if some of them belong in
Kahler’s corner, that would be far from enough. Taken as
a whole, the common-law cases reveal no settled consensus
favoring Kahler’s preferred insanity rule. And without
that, they cannot support his proposed constitutional
baseline.
Only with M’Naghten, in 1843, did a court articulate, and
momentum grow toward accepting, an insanity defense
based independently on moral incapacity. See Clark, 548
U. S., at 749; Leland, 343 U. S., at 801; supra, at 2, 8. The
M’Naghten test, as already described, found insanity in ei-
ther of two circumstances. See supra, at 1–2. A defendant
was acquitted if he “labour[ed] under such a defect of rea-
son, from disease of the mind, [1] as not to know the nature
and quality of the act he was doing; or, [2] if he did know it,
that he did not know he was doing what was wrong.” 10 Cl.
& Fin., at 210, 8 Eng. Rep., at 722 (emphasis added). That
test disaggregated the concepts of cognitive and moral inca-
pacity, so that each served as a stand-alone defense. And
its crisp two-part formulation proved influential, not only
in Great Britain but in the United States too. Over the
course of the 19th century, many States adopted the test,
making it the most popular one in the country.
Still, Clark unhesitatingly declared: “History shows no
deference to M’Naghten that could elevate its formula to the
level of fundamental principle.” 548 U. S., at 749. As Clark
elaborated, even M’Naghten failed to unify state insanity
defenses. See 548 U. S., at 749–752. States continued to
experiment with insanity rules, reflecting what one court
20 KAHLER v. KANSAS

Opinion of the Court

called “the infinite variety of forms [of] insanity” and the
“difficult and perplexing” nature of the defense. Roberts v.
State, 3 Ga. 310, 328, 332 (1847). Some States in the 1800s
gravitated to the newly emergent “volitional incapacity”
standard, focusing on whether the defendant could at all
control his actions. Clark, 548 U. S., at 749; see, e.g., Rob-
erts, 3 Ga., at 331. One court viewed that inquiry as “much
more practical” than the “right and wrong test,” which it
thought often “speculative and difficult of determination.”
State v. Felter, 25 Iowa 67, 82, 84 (1868); see Leland, 343
U. S., at 801 (recognizing such skepticism about the moral-
incapacity test); supra, at 8–9. Another prophesied that the
volitional test was the one “towards which all the modern
authorities in this country[ ] are gradually but surely tend-
ing.” Parsons, 81 Ala., at 586, 2 So., at 859. But that test,
too, failed to sweep all before it: State innovation proceeded
apace. See, e.g., State v. Pike, 49 N. H. 399, 442 (1870) (ap-
plying the “product” test, which excuses a defendant whose
crime “was the offspring or product of mental disease”);
N. D. Cent. Code Ann. §12.1–04.1–01(1)(a) (2012) (replac-
ing the right-from-wrong test with an inquiry into whether
the defendant’s act arose from “[a] serious distortion of
[his] capacity to recognize reality”). Much as medical views
of mental illness changed as time passed, so too did legal
views of how to account for that illness when assigning
blame.
As earlier noted, even the States that adopted M’Nagh-
ten soon divided on what its second prong should mean.
See supra, at 2–3. Most began by asking, as Kahler does,
about a defendant’s ability to grasp that his act was im-
moral. See, e.g., Wright v. State, 4 Neb. 407, 409 (1876);
State v. Spencer, 21 N. J. L. 196, 201 (1846). Thus, Clark
labeled M’Naghten’s second prong a test of “moral capac-
ity,” and invoked the oft-used phrase “telling right from
wrong” (or in older language, good from evil) to describe its
central inquiry. 548 U. S., at 747, 753; see supra, at 2. But
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Opinion of the Court

over the years, 16 States have reoriented the test to focus
on the defendant’s understanding that his act was illegal—
that is, legally rather than morally “wrong.”10 They thereby
excluded from the ranks of the insane those who knew an
act was criminal but still thought it right.
Contrary to Kahler’s (and the dissent’s) contention, that
difference matters. See Reply Brief 7 (claiming that “there
is little daylight between these inquiries”); post, at 17, 21
(same). The two tests will treat some, even though not all,
defendants in opposite ways. And the defendants they will
treat differently are exactly those Kahler (and the dissent)
focus on: those who know exactly what they are doing (in-
cluding that it is against the law) but believe it morally jus-
tified—because, say, it is commanded by God (or in the dis-
sent’s case, a dog). See Brief for Petitioner 15; post, at 20;
Schmidt, 216 N. Y., at 339, 110 N. E., at 949.11 A famed
——————
10 See State v. Skaggs, 120 Ariz. 467, 472, 586 P. 2d 1279, 1284 (1978);

Wallace v. State, 766 So. 2d 364, 367 (Fla. App. 2000); State v. Hamann,
285 N. W. 2d 180, 184 (Iowa 1979); Commonwealth v. Lawson, 475 Mass.
806, 811, 62 N. E. 3d 22, 28 (2016); State v. Worlock, 117 N. J. 596, 610–
611, 569 A. 2d 1314, 1322 (1990); People v. Wood, 12 N. Y. 2d 69, 76, 187
N. E. 2d 116, 121–122 (1962); State v. Carreiro, 2013–Ohio–1103, 988
N. E. 2d 21, 27 (App.); McElroy v. State, 242 S. W. 883, 884 (Tenn. 1922);
McAfee v. State, 467 S. W. 3d 622, 636 (Tex. Crim. App. 2015); State v.
Crenshaw, 98 Wash. 2d 789, 794–795, 659 P. 2d 488, 492–493 (1983);
Ark. Code Ann. §5–2–301(6) (2017); Ill. Comp. Stat., ch. 720, §5/6–2(a)
(West 2016); Ky. Rev. Stat. Ann. §504.020(1) (West 2016); Md. Crim.
Proc. Code Ann. §3–109(a) (2018); Ore. Rev. Stat. §161.295(1) (2019); Vt.
Stat. Ann., Tit. 13, §4801(a)(1) (2019).
11 The great judge (later Justice) whom the dissent cites to suggest

there is no real difference between the legal wrong and moral wrong tests
wrote a lengthy opinion whose point was the opposite. Consider a case,
Judge Cardozo said: “A mother kills her infant child to whom she has
been devotedly attached. She knows the nature and quality of the act;
she knows that the law condemns it; but she is inspired by an insane
delusion that God has appeared to her and ordained the sacrifice.” Peo-
ple v. Schmidt, 216 N. Y. 324, 339, 110 N. E. 945, 949 (1915). If the legal
wrong test were used, Judge Cardozo continued, “it would be the duty of
a jury to hold her responsible for the crime.” Ibid. But not if the focus
22 KAHLER v. KANSAS

Opinion of the Court

theorist of criminal law put the point this way:
“A kills B knowing that he is killing B, and knowing
that it is illegal to kill B, but under an insane delusion
that the salvation of the human race will be obtained
by . . . the murder of B[.] A’s act is a crime if the word
‘wrong’ [in M’Naghten] means illegal. It is not a crime
if the word wrong means morally wrong.” 2 J. Stephen,
History of the Criminal Law of England, ch. 19, p. 149
(1883).
So constitutionalizing the moral-incapacity standard, as
Kahler requests, would require striking down not only the
five state laws like Kansas’s (as the dissent at times sug-
gests, see post, at 16), but 16 others as well (as the dissent
eventually concedes is at least possible, see post, at 21).
And with what justification? The emergence of M’Nagh-
ten’s legal variant, far from raising a due process problem,
merely confirms what Clark already recognized. Even after
its articulation in M’Naghten (much less before), the moral-
incapacity test has never commanded the day. Clark, 548
U. S., at 749.12
——————
was, as in the original M’Naghten test, on moral wrong. And that differ-
ence led the New York Court of Appeals to hold that the trial court’s jury
instruction was in error. See 216 N. Y., at 340, 110 N. E., at 950. The
additional cases the dissent cites to downplay the distinction between
moral and legal wrong in fact follow Schmidt in recognizing when they
diverge. See Worlock, 117 N. J., at 611, 569 A. 2d, at 1322 (explaining
that “the distinction between moral and legal wrong may be critical”
when, for example, a defendant “knowingly kill[s] another in obedience
to a command from God”); Crenshaw, 98 Wash. 2d, at 798, 659 P. 2d, at
494 (acknowledging Schmidt’s view that even when a defendant “knows
that the law and society condemn [her] act,” she should not be held re-
sponsible if “her free will has been subsumed by her belief in [a] deific
decree”).
12 The diversity of American approaches to insanity is also evident in

the States’ decisions about which kinds of mental illness can support the
defense. See Clark, 548 U. S., at 750, n. 11; supra, at 3, n. 1. Some States
limit the defense to those with a “severe” mental disease. See, e.g., Ala.
 Cite as: 589 U. S. ____ (2020) 23

Opinion of the Court

Indeed, just decades ago Congress gave serious consider-
ation to adopting a mens rea approach like Kansas’s as the
federal insanity rule. See United States v. Pohlot, 827 F. 2d
889, 899, and n. 9 (CA3 1987) (describing bipartisan sup-
port for that proposal). The Department of Justice at the
time favored that version of the insanity test. Perhaps
more surprisingly, the American Medical Association did
too. And the American Psychiatric Association took no po-
sition one way or the other. Although Congress chose in the
end to adhere to the M’Naghten rule, the debate over the
bill itself reveals continuing division over the proper scope
of the insanity defense.
Nor is that surprising, given the nature of the inquiry. As
the American Psychiatric Association once noted, “insanity
is a matter of some uncertainty.” Insanity Defense Work
Group, Statement on the Insanity Defense, 140 Am. J.
Psych. 681, 685 (1983). Across both time and place, doctors
and scientists have held many competing ideas about men-
tal illness. And that is only the half of it. Formulating an
insanity defense also involves choosing among theories of
moral and legal culpability, themselves the subject of recur-
rent controversy. At the juncture between those two
spheres of conflict and change, small wonder there has not

——————
Code §13A–3–1 (2015). Others prohibit its assertion by defendants with
specific mental disorders. See, e.g., Ariz. Rev. Stat. Ann. §13–502 (2010)
(“psychosexual” or “impulse control disorders”); Ore. Rev. Stat.
§161.295(2) (“personality disorders”). In particular, many States follow
the Model Penal Code in prohibiting psychopaths from raising the de-
fense. See ALI, Model Penal Code §4.01(2), p. 163 (1985); e.g., Ind. Code
§35–41–3–6(b) (2019) (“abnormality manifested only by repeated unlaw-
ful or otherwise antisocial conduct”). All those limitations apply even
when the defendant’s mental illness prevented him from recognizing
that his crime was immoral. In that way too, many States have departed
from the principle that Kahler (along with the dissent) claims the Con-
stitution commands.
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Opinion of the Court

been the stasis Kahler sees—with one version of the insan-
ity defense entrenched for hundreds of years.
And it is not for the courts to insist on any single criterion
going forward. We have made the point before, in Leland,
Powell, and Clark. See supra, at 7–9. Just a brief reminder:
“[F]ormulating a constitutional rule would reduce, if not
eliminate, [the States’] fruitful experimentation, and freeze
the developing productive dialogue between law and psy-
chiatry into a rigid constitutional mold.” Powell, 392 U. S.,
at 536–537. Or again: In a sphere of “flux and disagree-
ment,” with “fodder for reasonable debate about what the
cognate legal and medical tests should be,” due process im-
poses no one view of legal insanity. Clark, 548 U. S., at
752–753. Defining the precise relationship between crimi-
nal culpability and mental illness involves examining the
workings of the brain, the purposes of the criminal law, the
ideas of free will and responsibility. It is a project demand-
ing hard choices among values, in a context replete with
uncertainty, even at a single moment in time. And it is a
project, if any is, that should be open to revision over time,
as new medical knowledge emerges and as legal and moral
norms evolve. Which is all to say that it is a project for state
governance, not constitutional law.
We therefore decline to require that Kansas adopt an in-
sanity test turning on a defendant’s ability to recognize that
his crime was morally wrong. Contrary to Kahler’s view,
Kansas takes account of mental health at both trial and
sentencing. It has just not adopted the particular insanity
defense Kahler would like. That choice is for Kansas to
make—and, if it wishes, to remake and remake again as the
future unfolds. No insanity rule in this country’s heritage
or history was ever so settled as to tie a State’s hands cen-
turies later. For that reason, we affirm the judgment below.

It is so ordered.
 Cite as: 589 U. S. ____ (2020) 1

BREYER, J., dissenting

SUPREME COURT OF THE UNITED STATES
_________________

No. 18–6135
_________________

JAMES K. KAHLER, PETITIONER v. KANSAS
ON WRIT OF CERTIORARI TO THE SUPREME COURT OF KANSAS
[March 23, 2020]

JUSTICE BREYER, with whom JUSTICE GINSBURG and
JUSTICE SOTOMAYOR join, dissenting.
Like the Court, I believe that the Constitution gives the
States broad leeway to define state crimes and criminal pro-
cedures, including leeway to provide different definitions
and standards related to the defense of insanity. But here,
Kansas has not simply redefined the insanity defense.
Rather, it has eliminated the core of a defense that has
existed for centuries: that the defendant, due to mental ill-
ness, lacked the mental capacity necessary for his conduct to be
considered morally blameworthy. Seven hundred years of
Anglo-American legal history, together with basic princi-
ples long inherent in the nature of the criminal law itself,
convince me that Kansas’ law “ ‘offends . . . principle[s] of
justice so rooted in the traditions and conscience of our peo-
ple as to be ranked as fundamental.’ ” Leland v. Oregon,
343 U. S. 790, 798 (1952) (quoting Snyder v. Massachusetts,
291 U. S. 97, 105 (1934)).
I
A much-simplified example will help the reader under-
stand the conceptual distinction that is central to this case.
Consider two similar prosecutions for murder. In Prosecu-
tion One, the accused person has shot and killed another
person. The evidence at trial proves that, as a result of se-
vere mental illness, he thought the victim was a dog. Pros-
ecution Two is similar but for one thing: The evidence at
2 KAHLER v. KANSAS

BREYER, J., dissenting

trial proves that, as a result of severe mental illness, the
defendant thought that a dog ordered him to kill the victim.
Under the insanity defense as traditionally understood, the
government cannot convict either defendant. Under Kan-
sas’ rule, it can convict the second but not the first.
To put the matter in more explicitly legal terms, consider
the most famous statement of the traditional insanity de-
fense, that contained in M’Naghten’s Case, 10 Cl. & Fin.
200, 8 Eng. Rep. 718 (H. L. 1843). Lord Chief Justice Tin-
dal, speaking for a majority of the judges of the common-
law courts, described the insanity defense as follows:
“[T]o establish a defence on the ground of insanity, it
must be clearly proved that, at the time of the commit-
ting of the act, the party accused was labouring under
such a defect of reason, from disease of the mind, [1] as
not to know the nature and quality of the act he was
doing; or, [2] 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 prong (sometimes referred to as “cognitive inca-
pacity”) asks whether the defendant knew what he was do-
ing. This prong corresponds roughly to the modern concept
of mens rea for many offenses. The second (sometimes re-
ferred to as “moral incapacity”) goes further. It asks, even
if the defendant knew what he was doing, did he have the
capacity to know that it was wrong? Applying this test to
my example, a court would find that both defendants suc-
cessfully established an insanity defense. Prosecution One
(he thought the victim was a dog) falls within M’Naghten’s
first prong, while Prosecution Two (he thought the dog or-
dered him to do it) falls within its second prong.
In Kansas’ early years of statehood, its courts recognized
the M’Naghten test as the “cardinal rule of responsibility in
the criminal law.” State v. Nixon, 32 Kan. 205, 206, 4
P. 159, 160 (1884). Kansas “steadfastly adhered to that
 Cite as: 589 U. S. ____ (2020) 3

BREYER, J., dissenting

test” for more than a century. State v. Baker, 249 Kan. 431,
449–450, 819 P. 2d 1173, 1187 (1991). But in 1995, Kansas
“ ‘legislatively abolish[ed] the insanity defense.’ ” State v.
Jorrick, 269 Kan. 72, 82, 4 P. 3d 610, 617 (2000) (quoting
Rosen, Insanity Denied: Abolition of the Insanity Defense
in Kansas, 8 Kan. J. L. & Pub. Pol’y 253, 254–255 (1997)).
Under the new provision, a criminal defendant’s mental
disease or defect is relevant to his guilt or innocence only
insofar as it shows that he lacked the intent defined as an
element of the offense, or mens rea. If the defendant acted
with the required level of intent, then he has no defense
based on mental illness. Kan. Stat. Ann. §21–5209 (2018
Cum. Supp.).
Under Kansas’ changed law, the defendant in Prosecu-
tion One could defend against the charge by arguing that
his mental illness prevented him from forming the mental
state required for murder (intentional killing of a human
being)—just as any defendant may attempt to rebut the
State’s prima facie case for guilt. The defendant in Prose-
cution Two has no defense. Because he acted with the req-
uisite level of intent, he must be convicted regardless of any
role his mental illness played in his conduct. See 307 Kan.
374, 401, 410 P. 3d 105, 125 (2018) (acknowledging that
Kansas’ mens rea approach “allows conviction of an individ-
ual who had no capacity to know that what he or she was
doing was wrong”).
I do not mean to suggest that M’Naghten’s particular ap-
proach to insanity is constitutionally required. As we have
said, “[h]istory shows no deference to M’Naghten.” Clark v.
Arizona, 548 U. S. 735, 749 (2006). M’Naghten’s second
prong is merely one way of describing something more fun-
damental. Its basic insight is that mental illness may so
impair a person’s mental capacities as to render him no
more responsible for his actions than a young child or a wild
animal. Such a person is not properly the subject of the
criminal law. As I shall explain in the following section,
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BREYER, J., dissenting

throughout history, the law has attempted to embody this
principle in a variety of ways. As a historical matter,
M’Naghten is by far its most prominent expression, but not
its exclusive one. Other ways of capturing it may well
emerge in the future. The problem with Kansas’ law is that
it excises this fundamental principle from its law entirely.
II
The Due Process Clause protects those “ ‘principle[s] of
justice so rooted in the traditions and conscience of our peo-
ple as to be ranked as fundamental.’ ” Leland, 343 U. S., at
798. Our “primary guide” in determining whether a princi-
ple of justice ranks as fundamental is “historical practice.”
Montana v. Egelhoff, 518 U. S. 37, 43 (1996) (plurality opin-
ion). The Court contends that the historical formulations
of the insanity defense were so diverse, so contested, as to
make it impossible to discern a unified principle that Kan-
sas’ approach offends. I disagree.
Few doctrines are as deeply rooted in our common-law
heritage as the insanity defense. Although English and
early American sources differ in their linguistic formula-
tions of the legal test for insanity, with striking consistency,
they all express the same underlying idea: A defendant
who, due to mental illness, lacks sufficient mental capacity
to be held morally responsible for his actions cannot be
found guilty of a crime. This principle remained embedded
in the law even as social mores shifted and medical under-
standings of mental illness evolved. Early American courts
incorporated it into their jurisprudence. The States even-
tually codified it in their criminal laws. And to this day, the
overwhelming majority of U. S. jurisdictions recognize in-
sanity as an affirmative defense that excuses a defendant
from criminal liability even where he was capable of form-
ing the mens rea required for the offense. See Appendix,
infra.
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BREYER, J., dissenting

A
Consider the established common-law background of the
insanity defense at and around the time the Framers wrote
the Constitution. The four preeminent common-law jurists,
Bracton, Coke, Hale, and Blackstone, each linked criminal-
ity to the presence of reason, free will, and moral under-
standing. It is “will and purpose,” wrote Henry de Bracton
in his 13th-century treatise, that “mark maleficia [mis-
deeds].” 2 Bracton On Laws and Customs of England 384
(S. Thorne transl. 1968) (Bracton); Oxford Latin Dictionary
1067 (P. Glare ed. 1982). A “madman,” he explained, “can
no more commit an injuria [unlawful conduct] or a felony
than a brute animal, since they are not far removed from
brutes.” 2 Bracton 424; Oxford Latin Dictionary, at 914.
Seizing on Bracton’s reference to “brute animals” (some-
times translated “wild beasts”), the Court concludes that
Bracton’s approach, like Kansas’, would excuse only those
who lack capacity to form any intention at all. See ante, at
15. But what does it mean to be like a “brute animal”? A
brute animal may well and readily intend to commit a vio-
lent act without being able to judge its moral nature. For
example, when a lion stalks and kills its prey, though it acts
intentionally, it does not offend against the criminal laws.
See 2 Bracton 379 (noting that “murder” is defined as “by
the hand of man” to “distinguish it from the case of
those slain or devoured by beasts and animals which lack
reason”).
Bracton’s other references to “madmen” shed further
light on the meaning he attached to that term. Bracton de-
scribed such persons as “without sense and reason” and
“lack[ing] animus.” Id., at 324, 424. And he likened a “lu-
natic” to an “infant,” who cannot be held liable in damages
unless he “is capable of perceiving the wrongful character
of his act.” Id., at 324; see also 4 id., at 356 (“in many ways
a minor and a madman are considered equals or not very
different, because they lack reason” (footnote omitted)).
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BREYER, J., dissenting

Thus, Bracton’s “brute animal” included those who lacked
the qualities of reason and judgment that make human be-
ings responsible moral agents. See Platt, The Origins and
Development of the “Wild Beast” Concept of Mental Illness
and Its Relation to Theories of Criminal Responsibility, 1
Issues in Crim. 1, 6 (1965).
Leaving Bracton, let us turn to Sir Edward Coke, writing
in the early 17th century. Coke wrote that “the act and
wrong of a mad man shall not be imputed to him,” not be-
cause he could not engage in intentional conduct (the equiv-
alent of the modern concept of mens rea), but because he
lacked something more—“mind or discretion.” 2 Institutes
of the Laws of England §405, p. 247b (1628). Coke, like
Bracton before him, likened a “mad man” to an “[i]nfant,”
who could not be punished as a criminal “untill he be of the
age of fourteene, which in Law is accounted the age of dis-
cretion.” Ibid. What is it that the “[i]nfant” lacks? Since
long before Coke’s time, English jurists and scholars be-
lieved that it was the moral nature, not the physical nature,
of an act that a young child is unlikely to understand. See
Platt & Diamond, The Origins of the “Right and Wrong”
Test of Criminal Responsibility and Its Subsequent Devel-
opment in the United States: An Historical Survey, 54 Cal.
L. Rev. 1227, 1233–1234 (1966) (Platt & Diamond).
Sir Matthew Hale also premised criminal liability on the
presence of “understanding and liberty of will,” without
which “there can be no transgression, or just reason to incur
the penalty or sanction that law instituted for the punish-
ment of the crimes or offenses.” 1 Pleas of the Crown, ch. 2,
pp. 14–15 (1736). Hale, too, likened insane persons to “in-
fants” under the age of 14, who were subject to the criminal
laws only if they “had discretion to judge between good and
evil.” Id., ch. 3, at 26–27; id., ch. 4, at 30 (a person who is
“labouring under melancholy distempers hath yet ordinar-
ily as great understanding, as ordinarily a child of fourteen
years hath, is such a person as may be guilty of treason or
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BREYER, J., dissenting

felony”). Those suffering from “total insanity” could not
be guilty of capital offenses, “for they have not the use of
understanding, and act not as reasonable creatures, but
their actions are in effect in the condition of brutes.” Id.,
at 30–32.
Sir William Blackstone, whose influence on the founding
generation was the most profound, was yet more explicit. A
criminal offense, he explained, requires both a “vitious will”
and a “vitious act.” 4 Commentaries on the Laws of Eng-
land 21 (1769). Persons suffering from a “deficiency in will”
arising from a “defective or vitiated understanding” were
“not [criminally] chargeable for their own acts.” Id., at 24.
Citing Coke, he explained that murder must be “committed
by a person of sound memory and discretion” because a “lu-
natic or infant” is “incapable of committing any crime, un-
less in such cases where they shew a consciousness of doing
wrong, and of course a discretion, or discernment, between
good and evil.” Id., at 195–196. And he opined that depri-
vation of “the capacity of discerning right from wrong” is
necessary “to form a legal excuse.” Id., at 189.
These four eminent jurists were not alone. Numerous
other commentators expressly linked criminal liability with
the accused’s capacity for moral agency. William Lam-
bard’s 1581 treatise ranked a “mad man” as akin to a
“childe” who had “no knowledge of good nor evil.” Eirenar-
cha, ch. 21, p. 218. If such a person killed a man, that is “no
felonious acte” because “they can[n]ot be said to have any
understanding wil[l].” Ibid. But if “upon examination” it
appeared that “they knew what they did, [and] it was ill,
the[n] seemeth it to be otherwise.” Ibid. (emphasis added).
Michael Dalton’s 1618 manual for justices of the peace in-
structed that “[i]f one that is Non compos mentis . . . kill a
man, this is no felonie; for they have no knowledge of good
and evill, nor can have a felonious intent, nor a will or mind
to do harme.” The Countrey Justice 215. William Hawkins,
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BREYER, J., dissenting

in 1716, wrote that “those who,” like “[l]unaticks,” are “un-
der a natural Disability of distinguishing between Good and
Evil . . . are not punishable by any criminal Prosecution
whatsoever.” 1 Pleas of the Crown §1, p. 2; see also id., at
1 (“The Guilt of offending against any Law whatsoever . . .
can never justly be imputed to those who are either unca-
pable of understanding it, or of conforming themselves to
it”).
English treatises on the law of mental disability adopted
the same view. George Collinson explained that “[t]o ex-
cuse a man in the commission of a crime, he must at the
period when he committed the offense, have been wholly in-
capable of distinguishing between good and evil, or of com-
prehending the nature of what he is doing.” Treatise on the
Law Concerning Idiots, Lunatics, and Other Persons Non
Compotes Mentis §7, p. 474 (1812) (Collinson); see also id.,
§2, at 471 (“[A]n evil intention is implied in every offence,
and constitutes the charge of every indictment: but a non
compos, not having a will of his own, cannot have an inten-
tion morally good or bad; so that the overt act by which
alone the motives of other men are discerned, with respect
to him proves nothing”). Similarly, Leonard Shelford, sum-
marizing English case law, wrote that “[t]he essence of a
crime consists in the animus or intention of the person who
commits it, considered as a free agent, and in a capacity of
distinguishing between moral good and evil.” Practical
Treatise on the Law Concerning Lunatics, Idiots, and Per-
sons of Unsound Mind 458 (1833) (emphasis deleted).
The majority believes that I am “cherry-pick[ing]” refer-
ences to moral understanding while ignoring references to
intent and mens rea. See ante, at 15–17, nn. 8, 9. With
respect, I disagree. The Court points out, correctly, that
many of the common-law sources state that the insane lack
mens rea or felonious intent. But what did they mean by
that? At common law, the term mens rea ordinarily incor-
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BREYER, J., dissenting

porated the notion of “general moral blameworthiness” re-
quired for criminal punishment. Sayre, Mens Rea, 45 Harv.
L. Rev. 974, 988 (1932); 3 Encyclopedia of Crime and Jus-
tice 995 (2d ed. 2002) (as used at common law, the term
mens rea “is synonymous with a person’s blameworthi-
ness”). The modern meaning of mens rea is narrower and
more technical. Ibid. It refers to the “state of mind or inat-
tention that, together with its accompanying conduct, the
criminal law defines as an offense.” Ibid. When common-
law writers speak of intent or mens rea, we cannot simply
assume that they use those terms in the modern sense.
That is an anachronism. Instead, we must examine the
context to understand what meaning they ascribed to those
terms. And when we do so, we see that, over and over again,
they link criminal intent to the presence of free will and
moral understanding. The Court dismisses those passages
as just “some ‘good and evil’ language.” Ante, at 17, n. 9.
But it fails to explain why, if mens rea in the modern sense
were sufficient, these common-law writers discuss the role
of moral agency at all, much less why such language ap-
pears in virtually every treatise and virtually every case.
In the Court’s view, all that is just spilled ink.
The English case law illustrates this point. In the semi-
nal case of Rex v. Arnold, 16 How. St. Tr. 695 (1724), the
defendant stood accused of shooting Lord Onslow while la-
boring under the insane delusion that Onslow had be-
witched him. Id., at 699, 721. The Court emphasizes Jus-
tice Tracy’s statement to the jury that if a man is “ ‘deprived
of his reason, and consequently of his intention, he cannot
be guilty,’ ” concluding that the court adopted a modern
mens rea test. Ante, at 16. But in the passage immediately
preceding that statement, Justice Tracy explained that the
defendant’s intent to shoot was clearly proved, and that the
only remaining question was whether his mental illness ex-
cused him from blame:
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BREYER, J., dissenting

“That he shot, and that wilfully [is proved]: but
whether maliciously, that is the thing: that is the ques-
tion; whether this man hath the use of his reason and
sense? If he was under the visitation of God, and could
not distinguish between good and evil, and did not
know what he did, though he committed the greatest
offence, yet he could not be guilty of any offence against
any law whatsoever; for guilt arises from the mind, and
the wicked will and intention of the man. If a man be
deprived of his reason, and consequently of his inten-
tion, he cannot be guilty; and if that be the case, though
he had actually killed my lord Onslow, he is exempted
from punishment.” 16 How. St. Tr., at 764 (emphasis
added; brackets in original).
See also ibid. (summarizing the testimony of one Mr. Coe,
who testified that he went to the defendant three days after
the shooting “and asked him, If he intended to kill my lord
Onslow? and he said, Yes, to be sure”). On the next page,
Justice Tracy concluded that the jury must determine
whether the evidence “doth shew a man, who knew what he
was doing, and was able to distinguish whether he was do-
ing good or evil, and understood what he did.” Id., at 765.
Likewise, in the case of Rex v. Lord Ferrers, 19 How. St.
Tr. 886 (1760), the solicitor general instructed the members
of the House of Lords to consider the “ ‘capacity and inten-
tion’ ” of the accused, to be sure, ante, at 17, but what did he
mean by those terms? The ultimate question of insanity,
he explained, depended on the defendant’s capacity at the
time of the offense to distinguish right from wrong:
“My lords, the question therefore must be asked; is the
noble prisoner at the bar to be acquitted from the guilt
of murder, on account of insanity? It is not pretended
to be a constant general insanity. Was he under the
power of it, at the time of the offence committed? Could
he, did he, at that time, distinguish between good and
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BREYER, J., dissenting

evil?” 19 How. St. Tr., at 948.
In summation, the solicitor general argued that Lord Fer-
rers’ own witnesses failed to provide any testimony “which
proves his lunacy or insanity at any time.” Id., at 952. Re-
viewing the pertinent evidence, he noted that one witness
testified that he “had observed great oddities in my lord,”
but acknowledged that he “never saw him in such a situa-
tion, as not to be capable of distinguishing between good
and evil, and not to know, that murder was a great crime.”
Ibid. Another admitted under questioning by the Lords
that “he thought lord Ferrers capable of distinguishing be-
tween moral and immoral actions.” Ibid. The defendant’s
brother was the only witness to testify that “at particular
times, the noble lord might not be able to distinguish be-
tween moral good and evil,” but even he, the solicitor gen-
eral argued, had been unable to testify to “any instance
within his own recollection.” Id., at 953. If Lord Ferrers’
bare intention to kill were sufficient to convict, why the ex-
tensive discussion of the evidence concerning his capacity
for moral understanding?
These examples reflect the prevailing view of the law
around the time of the founding. Judges regularly in-
structed juries that the defendant’s criminal liability de-
pended on his capacity for moral responsibility. See, e.g.,
Trial of Samuel Burt (July 19, 1786), in 6 Old Bailey Pro-
ceedings 875 (E. Hodgson ed. 1788) (to acquit based on in-
sanity, it must be shown that the mental disorder “takes
away from the party all moral agency and accountability,”
and “destroys in them, for the time at least, all power of
judging between right and wrong”); Trial of Francis Parr
(Jan. 15, 1787), 2 id., at 228 (jury must “judge whether at
the moment of committing [the offense] he was not a moral
agent, capable of discerning between good and evil, and of
knowing the consequences of what he did”); Bowler’s Case,
1 Collinson 673–674, n. (judge “concluded by observing to
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BREYER, J., dissenting

the jury, that it was for them to determine whether the
Prisoner, when he committed the offence with which he
stood charged, was or was not incapable of distinguishing
right from wrong”). The government’s attorneys agreed
that this was the proper inquiry. See, e.g., Parker’s Case, 1
id., at 479–480 (the Attorney General argued that “the jury
must be perfectly satisfied, that at the time when the crime
was committed, the prisoner did not really know right from
wrong”).
In none of the common-law cases was the judge’s refer-
ence to the defendant’s capacity for moral agency simply a
proxy for the narrow modern notion of mens rea. See ante,
at 17. Something more was required. Consider Belling-
ham’s Case, 1 Collinson 636. The defendant stood accused
of the murder of Spencer Perceval, the Chancellor of the Ex-
chequer, in the lobby of the House of Commons. Ibid. The
Court emphasizes Chief Justice Mansfield’s statement that
one who could not distinguish right from wrong “ ‘could have
no intention at all,’ ” concluding that Chief Justice Mans-
field viewed moral incapacity as a symptom of cognitive
breakdown rather than a test of insanity. Ante, at 18. But,
as in Rex v. Arnold, see supra, at 9–10, the defendant’s in-
tention to shoot Perceval was not seriously in dispute. 1
Collinson 670. Instead, his guilt or innocence turned on his
capacity for moral blame. The “single question” for the jury,
charged the Chief Justice, “was whether, when [the defend-
ant] committed the offence charged upon him, he had suffi-
cient understanding to distinguish good from evil, right
from wrong, and that murder was a crime not only against
the law of God, but against the law of his Country.” Id., at
673. Lord Lyndhurst, presiding over the case of Rex v. Of-
ford, 5 Car. & P. 168, 172 Eng. Rep. 924 (N. P. 1831), cer-
tainly understood that inquiry to be the crux of Chief Jus-
tice Mansfield’s charge. Citing Bellingham’s Case, he
instructed the jury that “[t]he question was, did [the ac-
cused] know that he was committing an offence against the
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BREYER, J., dissenting

laws of God and nature?” 5 Car. & P., at 168, 172 Eng. Rep.,
at 925.
The Court dismisses other common-law cases as failing
to articulate a clear legal standard. See ante, at 18–19. But
these cases, too, required more than bare intent. In Had-
field’s Case, 27 How. St. Tr. 1281 (1800), the defendant was
acquitted after the prosecution conceded that he was “in a
deranged state of mind” when he shot at King George III.
Id., at 1353. And in Regina v. Oxford, 9 Car. & P. 525, 173
Eng. Rep. 941 (N. P. 1840), the court observed that a “per-
son may commit a criminal act, and yet not be responsible.”
Id., at 546, 173 Eng. Rep., at 950. Although it acknowl-
edged the difficulty of “lay[ing] down the rule of the English
law on the subject,” it summed up the inquiry as “whether
the prisoner was labouring under that species of insanity
which satisfies you that he was quite unaware of the na-
ture, character, and consequences of the act he was commit-
ting, or, in other words, whether he was under the influence
of a diseased mind, and was really unconscious at the time
he was committing the act, that it was a crime.” Id., at 546–
547, 173 Eng. Rep., at 950. Although these and other Eng-
lish cases discuss insanity in terms that are less precise
than our modern taxonomy of mental states, their lesson is
clear. To be guilty of a crime, the accused must have some-
thing more than bare ability to form intentions and carry
them out.
B
These fundamental principles of criminal responsibility
were incorporated into American law from the early days of
the Republic. Early American commentaries on the crimi-
nal law generally consisted of abridgments of the works of
prominent English jurists. As early as 1792, one such
abridgment instructed that “lunaticks, who are under a
natural disability of distinguishing between good and evil
are not punishable by any criminal prosecution.” R. Burn,
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BREYER, J., dissenting

Abridgment, or the American Justice 300; see also W.
Stubbs, Crown Circuit Companion 288 (1 Am. ed. 1816) (“If
one that is non compos mentis . . . kill a man, this is no fel-
ony; for they have not knowledge of good and evil, nor can
have a felonious intent, nor a will or mind to do harm”).
And an influential founding-era legal dictionary described
the “general rule” that lunatics, “being by reason of their
natural disabilities incapable of judging between good and
evil, are punishable by no criminal prosecution whatso-
ever.” 2 T. Cunningham, New and Complete Law
Dictionary (2d corr. ed. 1771). Similarly, the first compre-
hensive American text on forensic medicine, published in
1823, cited Chief Justice Mansfield’s charge to the jury in
Bellingham’s Case for the proposition that “[s]o long as they
could distinguish good from evil, so long would they be an-
swerable for their conduct.” 1 T. Beck, Elements of Medical
Jurisprudence 369. These principles, it concluded, “are
doubtless correct, and conducive to the ends of justice.” Id.,
at 370.
Early American jurists closely hewed to these principles.
In case after case, judges instructed juries that they must
inquire into the defendant’s capacity for moral understand-
ing. See, e.g., Meriam’s Case, 7 Mass. 168 (1810), 6 N. Y.
City-Hall Recorder 162 (1822) (whether the defendant was
“at the time, capable of distinguishing good from evil”);
Clark’s Case, 1 N. Y. City-Hall Recorder 176, 177 (1816)
(same); Ball’s Case, 2 N. Y. City-Hall Recorder 85, 86 (1817)
(same); United States v. Clarke, 25 F. Cas. 454 (No. 14,811)
(CC DC 1818) (whether defendant was “in such a state of
mental insanity . . . as not to have been conscious of the
moral turpitude of the act”); Cornwell v. State, 8 Tenn. 147,
155 (1827) (whether the prisoner “had not sufficient under-
standing to know right from wrong”).
C
As the foregoing demonstrates, by the time the House of
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BREYER, J., dissenting

Lords articulated the M’Naghten test in 1843, its “essential
concept and phraseology” were “already ancient and thor-
oughly embedded in the law.” Platt & Diamond 1258; see
also 1 W. Russell, Crimes and Misdemeanors 8–14 (3d ed.
1843) (summarizing the pre-M’Naghten English case law
and concluding that the key questions were whether “there
be thought and design, a faculty to distinguish the nature
of actions, [and] to discern the difference between moral
good and evil”). Variations on the M’Naghten rules soon
became the predominant standard in the existing states of
the United States. Platt & Diamond 1257. That tradition
has continued, almost without exception, to the present
day.
It is true that, even following M’Naghten, States contin-
ued to experiment with different formulations of the insan-
ity defense. See ante, at 19–20. Some adopted the volitional
incapacity, or “irresistible-impulse,” test. But those States
understood that innovation to expand, not contract, the
scope of the insanity defense, excusing not only defendants
who met some variant of the traditional M’Naghten test but
also those who understood that their conduct was wrong but
were incapable of restraint. See, e.g., Parsons v. State, 81
Ala. 577, 584–585, 2 So. 854, 858–859 (1887); Bradley v.
State, 31 Ind. 492, 507–508 (1869); State v. Felter, 25 Iowa
67, 82–83 (1868); Hopps v. People, 31 Ill. 385, 391–392
(1863).
So too, the “offspring” or “product” test, which asks
whether the defendant’s conduct was attributable to mental
disease or defect. The States that adopted this test did so
out of the conviction that the M’Naghten test was too re-
strictive in its approach to assessing the accused’s capacity
for criminal responsibility. See Durham v. United States,
214 F. 2d 862, 874 (CADC 1954) (“We conclude that a
broader test should be adopted”); State v. Pike, 49 N. H. 399,
441–442 (1870); see also Reid, Understanding the New
Hampshire Doctrine of Criminal Insanity, 69 Yale L. J. 367,
16 KAHLER v. KANSAS

BREYER, J., dissenting

386 (1960) (“[T]he New Hampshire doctrine . . . is more lib-
eral and has a wider range than M’Naghten rules”). Even
as States experimented with broader insanity rules, they
retained the core of the traditional common-law defense.
In the early 20th century, several States attempted to
break with that tradition. The high courts of those States
quickly struck down their restrictive laws. As one justice of
the Mississippi Supreme Court wrote in 1931: The “common
law proceeds upon an idea that before there can be a crime
there must be an intelligence capable of comprehending the
act prohibited, and the probable consequence of the act, and
that the act is wrong.” Sinclair v. State, 161 Miss. 142, 158,
132 So. 581, 583 (Ethridge, J., concurring). Accordingly,
Justice Ethridge said, insanity “has always been a complete
defense to all crimes from the earliest ages of the common
law.” Ibid.; State v. Strasburg, 60 Wash. 106, 116, 110 P.
1020, 1022–1023 (1910); cf. State v. Lange, 168 La. 958, 965,
123 So. 639, 642 (1929).
Today, 45 States, the Federal Government, and the Dis-
trict of Columbia continue to recognize an insanity defense
that retains some inquiry into the blameworthiness of the
accused. Seventeen States and the Federal Government
use variants of the M’Naghten test, with its alternative cog-
nitive and moral incapacity prongs. Three States have
adopted M’Naghten plus the volitional test. Ten States rec-
ognize a defense based on moral incapacity alone. Thirteen
States and the District of Columbia have adopted variants
of the Model Penal Code test, which combines volitional in-
capacity with an expanded version of moral incapacity. See
Appendix, infra. New Hampshire alone continues to use
the “product” test, asking whether “a mental disease or de-
fect caused the charged conduct.” State v. Fichera, 153
N. H. 588, 593, 903 A. 2d 1030, 1035 (2006). This broad test
encompasses “ ‘whether the defendant knew the difference
between right and wrong and whether the defendant acted
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BREYER, J., dissenting

impulsively,’ ” as well as “ ‘whether the defendant was suf-
fering from delusions or hallucinations.’ ” State v. Cegelis,
138 N. H. 249, 255, 638 A. 2d 783, 786 (1994). And North
Dakota uses a unique formulation that asks whether the
defendant “lacks substantial capacity to comprehend the
harmful nature or consequences of the conduct, or the con-
duct is the result of a loss or serious distortion of the indi-
vidual’s capacity to recognize reality.” N. D. Cent. Code
Ann. §12.1–04.1–01(1) (2012).
Of the States that have adopted the M’Naghten or Model
Penal Code tests, some interpret knowledge of wrongful-
ness to refer to moral wrong, whereas others hold that it
means legal wrong. See ante, at 2–3, 20–22. While there
is, of course, a logical distinction between those interpreta-
tions, there is no indication that it makes a meaningful dif-
ference in practice. The two inquiries are closely related
and excuse roughly the same universe of defendants. See
State v. Worlock, 117 N. J. 596, 609–611, 569 A. 2d 1314,
1321–1322 (1990) (“In most instances, legal wrong is coex-
tensive with moral wrong”); State v. Crenshaw, 98 Wash. 2d
789, 799, 659 P. 2d 488, 494 (1983) (“ ‘[S]ince by far the vast
majority of cases in which insanity is pleaded as a defense
to criminal prosecutions involves acts which are universally
recognized as morally wicked as well as illegal, the hair-
splitting distinction between legal and moral wrong need
not be given much attention’ ”); People v. Schmidt, 216 N. Y.
324, 340, 110 N. E. 945, 949 (1915) (Cardozo, J.)
(“Knowledge that an act is forbidden by law will in most
cases permit the inference of knowledge that, according to
the accepted standards of mankind, it is also condemned as
an offense against good morals”); see also ALI, Model Penal
Code §4.01, Explanatory Note, p. 164 (1985) (explaining
that “few cases are likely to arise in which the variation will
be determinative”).
18 KAHLER v. KANSAS

BREYER, J., dissenting

III
A
Consider the basic reason that underlies and explains
this long legal tradition. That reason reveals that more is
at stake than its duration alone. The tradition reflects the
fact that a community’s moral code informs its criminal law.
As Henry Hart stated it, the very definition of crime is con-
duct that merits “a formal and solemn pronouncement of
the moral condemnation of the community.” The Aims of
the Criminal Law, 23 Law & Contemp. Prob. 401, 405
(1958).
The criminal law does not adopt, nor does it perfectly
track, moral law. It is no defense simply to claim that one’s
criminal conduct was morally right. But the criminal law
nonetheless tries in various ways to prevent the distance
between criminal law and morality from becoming too
great. In the words of Justice Holmes, a law that “punished
conduct [that] would not be blameworthy in the average
member of the community would be too severe for that com-
munity to bear.” O. Holmes, The Common Law 50 (1881);
see also ibid. (“[T]o deny that criminal liability . . . is
founded on blameworthiness . . . would shock the moral
sense of any civilized community”).
Sometimes the criminal law seeks to keep its strictures
roughly in line with the demands of morality through
grants of discretion that will help it to reach appropriate
results in individual cases, including special instances
where the law points one way and morality the other. Thus,
prosecutors need not prosecute. Jurors (however in-
structed) may decide to acquit. Judges may exercise the
discretion the law allows them to impose a lenient sentence.
Executives may grant clemency.
And sometimes the law attempts to maintain this bal-
ance by developing and retaining a “collection of interlock-
ing and overlapping concepts,” including defenses, that will
help “assess the moral accountability of an individual for
 Cite as: 589 U. S. ____ (2020) 19

BREYER, J., dissenting

his antisocial deeds.” Powell v. Texas, 392 U. S. 514, 535–
536 (1968) (plurality opinion). These concepts and defenses
include “actus reus, mens rea, insanity, mistake, justifica-
tion, and duress.” Id., at 536.
As we have recognized, the “process of adjustment”
within and among these overlapping legal concepts “has al-
ways been thought to be the province of the States.” Ibid.
Matters of degree, specific content, and aptness of applica-
tion all may be, and have always been, the subject of legal
dispute. But the general purpose—to ensure a rough con-
gruence between the criminal law and widely accepted
moral sentiments—persists. To gravely undermine the in-
sanity defense is to pose a significant obstacle to this basic
objective.
The majority responds that Kansas has not removed the
element of blameworthiness from its treatment of insanity;
it has simply made a different judgment about what con-
duct is blameworthy. See ante, at 13, n. 7. That is not how
the Kansas Supreme Court has characterized its law. See
State v. Bethel, 275 Kan. 456, 472, 66 P. 3d 840, 850 (2003)
(holding that Kansas law provides for “no consideration,” at
the guilt phase, “of whether wrongfulness was inherent in
the defendant’s intent”). In any event, as the Court
acknowledges, the States’ discretion in this area must be
constrained within “broad limits,” ante, at 7, which are de-
rived from history and tradition. The question is whether
Kansas’ approach transgresses those limits. I doubt that
the Court would declare, for example, that a State may do
away with the defenses of duress or self-defense on the
ground that, in its idiosyncratic judgment, they are not re-
quired. With respect to the defense of insanity, I believe
that our history shows clearly that the criminal law has al-
ways required a higher degree of individual culpability than
the modern concept of mens rea. See Part II, supra. And in
my view, Kansas’ departure from this long uniform tradi-
tion poses a serious problem.
20 KAHLER v. KANSAS

BREYER, J., dissenting

B
To see why Kansas’ departure is so serious, go back to our
two simplified prosecutions: the first of the defendant who,
because of serious mental illness, believes the victim is a
dog; the second of a defendant who, because of serious men-
tal illness, believes the dog commanded him to kill the vic-
tim. Now ask, what moral difference exists between the de-
fendants in the two examples? Assuming equivalently
convincing evidence of mental illness, I can find none at all.
In both cases, the defendants differ from ordinary persons
in ways that would lead most of us to say that they should
not be held morally responsible for their acts. I cannot find
one defendant more responsible than the other. And for
centuries, neither has the law.
More than that, scholars who have studied this subject
tell us that examples of the first kind are rare. See Brief
for 290 Criminal Law and Mental Health Law Professors as
Amici Curiae 12. Others repeat this claim. See Slobogin,
An End to Insanity: Recasting the Role of Mental Disability
in Criminal Cases, 86 Va. L. Rev. 1199, 1205 (2000); Morse,
Mental Disorder and Criminal Law, 101 J. Crim. L. & C.
885, 933 (2011). That is because mental illness typically
does not deprive individuals of the ability to form intent.
Rather, it affects their motivations for forming such intent.
Brief for 290 Criminal Law and Mental Health Law Profes-
sors as Amici Curiae 12. For example, the American Psy-
chiatric Association tells us that individuals suffering from
mental illness may experience delusions—erroneous per-
ceptions of the outside world held with strong conviction.
They may believe, incorrectly, that others are threatening
them harm (persecutory delusions), that God has com-
manded them to engage in certain conduct (religious delu-
sions), or that they or others are condemned to a life of suf-
fering (depressive delusions). Brief for American
Psychiatric Association et al. as Amici Curiae 25–26. Such
delusions may, in some cases, lead the patient to behave
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BREYER, J., dissenting

violently. Id., at 28. But they likely would not interfere
with his or her perception in such a way as to negate mens
rea. See H. R. Rep. No. 98–577, p. 15 n. 23 (1984) (“Mental
illness rarely, if ever, renders a person incapable of under-
standing what he or she is doing. Mental illness does not,
for example, alter the perception of shooting a person to
that of shooting a tree.”).
Kansas’ abolition of the second part of the M’Naghten test
requires conviction of a broad swath of defendants who are
obviously insane and would be adjudged not guilty under
any traditional form of the defense. This result offends
deeply entrenched and widely recognized moral principles
underpinning our criminal laws. See, e.g., National
Comm’n on Reform of Fed. Crim. Laws, Final Report, Pro-
posed New Fed. Crim. Code §503, pp. 40–41 (1971) (to at-
tribute guilt to a “manifestly psychotic person” would “be
immoral and inconsistent with the aim of a criminal code”);
H. R. Rep. No. 98–577, at 7–8 (“[T]he abolition of the affirm-
ative insanity defense would alter that fundamental basis
of Anglo-American criminal law: the existence of moral cul-
pability as a prerequisite for punishment”); ABA Criminal
Justice Mental Health Standards §7–6.1, pp. 336–338
(1989) (rejecting the mens rea approach “out of hand” as “a
jarring reversal of hundreds of years of moral and legal
history” that “inhibits if not prevents the exercise of hu-
mane judgment that has distinguished our criminal law
heritage”).
By contrast, the rule adopted by some States that a de-
fendant must be acquitted if he was unable to appreciate
the legal wrongfulness of his acts, see ante, at 20–22, would
likely lead to acquittal in the mine run of such cases. See
supra, at 17. If that is so, then that rule would not pose the
same due process problem as Kansas’ approach. That issue
is not before us, as Kansas’ law does not provide even that
protection to mentally ill defendants.
22 KAHLER v. KANSAS

BREYER, J., dissenting

C
Kansas and the Solicitor General, in their efforts to jus-
tify Kansas’ change, make four important arguments.
First, they point to cases in this Court in which we have
said that the States have broad leeway in shaping the in-
sanity defense. See Leland, 343 U. S. 790; Clark, 548 U. S.
735. In Leland, we rejected the defendant’s argument that
the Constitution required the adoption of the “ ‘irresistible
impulse’ ” test. 343 U. S., at 800–801. Similarly, in Clark,
we upheld Arizona’s effort to eliminate the first part of the
M’Naghten rule, applicable to defendants whose mental ill-
ness deprived them of the ability to know the “ ‘nature and
quality of the act,’ ” 548 U. S., at 747–748. If Arizona can
eliminate the first prong of M’Naghten, Kansas asks, why
can Kansas not eliminate the second part?
The answer to this question lies in the fact that Arizona,
while amending the insanity provisions of its criminal code,
did not in practice eliminate the traditional insanity de-
fense in any significant part. See 548 U. S., at 752, n. 20
(reserving the question whether “the Constitution man-
dates an insanity defense”). As we pointed out, “cognitive
incapacity is itself enough to demonstrate moral incapac-
ity.” Id., at 753. Evidence that the defendant did not know
what he was doing would also tend to establish that he did
not know that it was wrong. Id., at 753–754. And Prosecu-
tion One (he thought the victim was a dog) would still fail.
The ability of the States to refuse to adopt other insanity
tests, such as the “irresistible impulse” test or the “product
of mental illness” test are also beside the point. See Leland,
343 U. S., at 800–801. Those tests both expand upon
M’Naghten’s principles. Their elimination would cut the
defense back to what it traditionally has been, not, as here,
eliminate its very essence.
Second, the United States as amicus curiae suggests that
the insanity defense is simply too difficult for juries to ad-
minister. Brief for United States as Amicus Curiae 12–13.
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BREYER, J., dissenting

Without doubt, assessing the defendant’s claim of insanity
is difficult. That is one reason I believe that States must
remain free to refine and redefine their insanity rules
within broad bounds. But juries have been making that de-
termination for centuries and continue to do so in 45 States.
And I do not see how an administrative difficulty can justify
abolishing the heart of the defense.
Third, Kansas argues that it has not abolished the insan-
ity defense or any significant part of it. It has simply moved
the stage at which a defendant can present the full range of
mental-capacity evidence to sentencing. See Brief for Re-
spondent 8; ante, at 4–5. But our tradition demands that
an insane defendant should not be found guilty in the first
place. Moreover, the relief that Kansas offers, in the form
of sentencing discretion and the possibility of commitment
in lieu of incarceration, is a matter of judicial discretion, not
of right. See State v. Maestas, 298 Kan. 765, 316 P. 3d 724
(2014). The insane defendant is, under Kansas law, ex-
posed to harsh criminal sanctions up to and including
death. And Kansas’ sentencing provisions do nothing to al-
leviate the stigma and the collateral consequences of a
criminal conviction.
Finally, Kansas argues that the insane, provided they are
capable of intentional action, are culpable and should be
held liable for their antisocial conduct. Brief for Respond-
ent 40. To say this, however, is simply to restate the con-
clusion for which Kansas argues in this case. It is a conclu-
sion that in my view runs contrary to a legal tradition that
embodies a fundamental precept of our criminal law and
that stretches back, at least, to the origins of our Nation.
For these reasons, with respect, I dissent.
24 KAHLER v. KANSAS

BREYER
Appendix to the, J., dissenting
opinion of BREYER, J.

APPENDIX
M’Naghten
State Text
Alabama “It is an affirmative defense to a prosecution for any
crime that, at the time of the commission of the acts con-
stituting the offense, the defendant, as a result of severe
mental disease or defect, was unable to appreciate the na-
ture and quality or wrongfulness of his acts.” Ala. Code
§13A–3–1(a) (2015).
California “In any criminal proceeding, including any juvenile
court proceeding, in which a plea of not guilty by reason
of insanity is entered, this defense shall be found by the
trier of fact only when the accused person proves by a pre-
ponderance of the evidence that he or she was incapable
of knowing or understanding the nature and quality of his
or her act and of distinguishing right from wrong at the
time of the commission of the offense.” Cal. Penal Code
Ann. §25(b) (West 2014).
Colorado “(1) The applicable test of insanity shall be:
“(a) A person who is so diseased or defective in mind at
the time of the commission of the act as to be incapable of
distinguishing right from wrong with respect to that act
is not accountable; except that care should be taken not
to confuse such mental disease or defect with moral obliq-
uity, mental depravity, or passion growing out of anger,
revenge, hatred, or other motives and kindred evil condi-
tions, for, when the act is induced by any of these causes,
the person is accountable to the law; or
“(b) A person who suffered from a condition of mind
caused by mental disease or defect that prevented the
person from forming a culpable mental state that is an
essential element of a crime charged, but care should be
taken not to confuse such mental disease or defect with
moral obliquity, mental depravity, or passion growing out
of anger, revenge, hatred, or other motives and kindred
evil conditions because, when the act is induced by any of
these causes, the person is accountable to the law.” Colo.
Rev. Stat. §16–8–101.5(1) (2019).
Florida “(1) AFFIRMATIVE DEFENSE.––All persons are pre-
sumed to be sane. It is an affirmative defense to a crimi-
nal prosecution that, at the time of the commission of the
acts constituting the offense, the defendant was insane.
Insanity is established when:
“(a) The defendant had a mental infirmity, disease, or
defect; and
“(b) Because of this condition, the defendant:
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Appendix to the, J.,
BREYER opinion of BREYER, J.
dissenting

State Text
“1. Did not know what he or she was doing or its conse-
quences; or
“2. Although the defendant knew what he or she was
doing and its consequences, the defendant did not know
that what he or she was doing was wrong.

“Mental infirmity, disease, or defect does not constitute a
defense of insanity except as provided in this subsection.”
Fla. Stat. §775.027 (2018).
Iowa “A person shall not be convicted of a crime if at the time
the crime is committed the person suffers from such a dis-
eased or deranged condition of the mind as to render the
person incapable of knowing the nature and quality of the
act the person is committing or incapable of distinguish-
ing between right and wrong in relation to that act.” Iowa
Code §701.4 (2016).
Minne- “No person having a mental illness or cognitive impair-
sota ment so as to be incapable of understanding the proceed-
ings or making a defense shall be tried, sentenced, or pun-
ished for any crime; but the person shall not be excused
from criminal liability except upon proof that at the time
of committing the alleged criminal act the person was la-
boring under such a defect of reason, from one of these
causes, as not to know the nature of the act, or that it was
wrong.” Minn. Stat. §611.026 (2019).
Missis- “In determining sanity in criminal cases Mississippi uti-
sippi lizes the common law M’Naghten test. Under the
M’Naghten test, the accused must be laboring under such
defect of reason from disease of the mind as (1) not to
know the nature and quality of the act he was doing or (2)
if he did not know it, that he did not know that what he
was doing was wrong.” Parker v. State, 273 So. 3d 695,
705–706 (Miss. 2019) (internal quotation marks and foot-
note omitted).
Missouri “A person is not responsible for criminal conduct if at the
time of such conduct as a result of mental disease or de-
fect he was incapable of knowing and appreciating the na-
ture, quality or wrongfulness of his or her conduct.” Mo.
Rev. Stat. §562.086(1) (2016).
Nebraska “Under our current common-law definition, the two re-
quirements for the insanity defense are that (1) the de-
fendant had a mental disease or defect at the time of the
crime and (2) the defendant did not know or understand
the nature and consequences of his or her actions or that
he or she did not know the difference between right and
wrong.” State v. Hotz, 281 Neb. 260, 270, 795 N. W. 2d
26 KAHLER v. KANSAS

Appendix to the, opinion
BREYER of BREYER, J.
J., dissenting

State Text
645, 653 (2011).
Nevada “To qualify as being legally insane, a defendant must be
in a delusional state such that he cannot know or under-
stand the nature and capacity of his act, or his delusion
must be such that he cannot appreciate the wrongfulness
of his act, that is, that the act is not authorized by law.”
Finger v. State, 117 Nev. 548, 576, 27 P. 3d 66, 84–85
(2001).
New “A person is not criminally responsible for conduct if at
Jersey the time of such conduct he was laboring under such a
defect of reason, from disease of the mind as not to know
the nature and quality of the act he was doing, or if he did
know it, that he did not know what he was doing was
wrong.” N. J. Stat. Ann. §2C:4–1 (West 2015).
New York “In any prosecution for an offense, it is an affirmative
defense that when the defendant engaged in the pro-
scribed conduct, he lacked criminal responsibility by rea-
son of mental disease or defect. Such lack of criminal re-
sponsibility means that at the time of such conduct, as a
result of mental disease or defect, he lacked substantial
capacity to know or appreciate either:
“1. The nature and consequences of such conduct; or
“2. That such conduct was wrong.” N. Y. Penal Law
Ann. §40.15 (West 2009).
North “[A]n accused is legally insane and exempt from criminal
Carolina responsibility by reason thereof if he commits an act
which would otherwise be punishable as a crime, and at
the time of so doing is laboring under such a defect of rea-
son, from disease of the mind, as to be incapable of know-
ing the nature and quality of the act he is doing, or, if he
does know this, incapable of distinguishing between right
and wrong in relation to such act.” State v. Thompson,
328 N. C. 477, 485–486, 402 S. E. 2d 386, 390 (1991).
Okla- “Oklahoma uses the M’Naghten test to determine the is-
homa sue of sanity at the time of the crime. This Court has held
that the M’Naghten insanity test, as applied in Okla-
homa, has two prongs. Under the first prong, the defend-
ant is considered insane if he is suffering from a mental
disability such that he does not know his acts are wrong
and he is unable to distinguish right from wrong with re-
spect to his acts. Under the second prong, the defendant
is considered insane if suffering from a disability of rea-
son or disease of the mind such that he does not under-
stand the nature or consequences of his acts or omissions.
The defendant need only satisfy one of these prongs in
order to be found not guilty by reason of insanity.”
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Appendix to the, J.,
BREYER opinion of BREYER, J.
dissenting

State Text
Cheney v. State, 909 P. 2d 74, 90 (Okla. 1995) (footnotes
omitted).
Pennsyl- “Common law M’Naghten’s Rule preserved.—Nothing in
vania this section shall be deemed to repeal or otherwise abro-
gate the common law defense of insanity (M’Naghten’s
Rule) in effect in this Commonwealth on the effective date
of this section.” 18 Pa. Cons. Stat. §314(d) (2015).
Tennes- “It is an affirmative defense to prosecution that, at the
see time of the commission of the acts constituting the of-
fense, the defendant, as a result of a severe mental dis-
ease or defect, was unable to appreciate the nature or
wrongfulness of the defendant’s acts.” Tenn. Code Ann.
§39–11–501(a) (2018).
Washing- “To establish the defense of insanity, it must be shown
ton that:
“(1) At the time of the commission of the offense, as a
result of mental disease or defect, the mind of the actor
was affected to such an extent that:
“(a) He or she was unable to perceive the nature and
quality of the act with which he or she is charged; or
“(b) He or she was unable to tell right from wrong with
reference to the particular act charged.” Wash. Rev. Code
§9A.12.010 (2015).
Federal “Affirmative Defense.—It is an affirmative defense to
a prosecution under any Federal statute that, at the time
of the commission of the acts constituting the offense, the
defendant, as a result of a severe mental disease or defect,
was unable to appreciate the nature and quality or the
wrongfulness of his acts.” 18 U. S. C. §17.

M’Naghten plus volitional incapacity
State Text
Georgia “A person shall not be found guilty of a crime if, at the
time of the act, omission, or negligence constituting the
crime, the person did not have mental capacity to distin-
guish between right and wrong in relation to such act,
omission, or negligence.” Ga. Code Ann. §16–3–2 (2019).
“A person shall not be found guilty of a crime when, at
the time of the act, omission, or negligence constituting
the crime, the person, because of mental disease, injury,
or congenital deficiency, acted as he did because of a de-
lusional compulsion as to such act which overmastered
his will to resist committing the crime.” §16–3–3.
New “In order to support a verdict of insanity under the
Mexico
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BREYER
Appendix to the, J., dissenting
opinion of BREYER, J.

State Text
M’Naghten test, the jury must be satisfied that the de-
fendant (1) did not know the nature and quality of the act
or (2) did not know that it was wrong. This rule prevailed
in New Mexico until 1954 when this court in State v.
White, 56 N. M. 324, 270 P. 2d 727 (1954) made a careful
analysis of the authorities and made a limited extension
of the M’Naghten rule, adding a third ingredient. The
court held that if the accused, (3) as a result of disease of
the mind ‘was incapable of preventing himself from com-
mitting’ the crime, he could be adjudged insane and
thereby relieved of legal responsibility for what would
otherwise be a criminal act.” State v. Hartley, 90 N. M.
488, 490, 565 P. 2d 658, 660 (1977).
Virginia “As applied in Virginia, the defense of insanity provides
that a defendant may prove that at the time of the com-
mission of the act, he was suffering from a mental disease
or defect such that he did not know the nature and quality
of the act he was doing, or, if he did know it, he did not
know what he was doing was wrong. . . . In addition, we
have approved in appropriate cases the granting of an in-
struction defining an ‘irresistible impulse’ as a form of le-
gal insanity. The irresistible impulse doctrine is applica-
ble only to that class of cases where the accused is able to
understand the nature and consequences of his act and
knows it is wrong, but his mind has become so impaired
by disease that he is totally deprived of the mental power
to control or restrain his act.” Orndorff v. Common-
wealth, 279 Va. 597, 601, n. 5, 691 S. E. 2d 177, 179, n. 5
(2010) (internal quotation marks and citations omitted).

Moral incapacity
State Text
Arizona “A person may be found guilty except insane if at the
time of the commission of the criminal act the person
was afflicted with a mental disease or defect of such se-
verity that the person did not know the criminal act was
wrong.” Ariz. Rev. Stat. Ann. §13–502(A) (2010).
Delaware “In any prosecution for an offense, it is an affirmative
defense that, at the time of the conduct charged, as a
result of mental illness or serious mental disorder, the
accused lacked substantial capacity to appreciate the
wrongfulness of the accused’s conduct.” Del. Code Ann.,
Tit. 11, §401(a) (2015).
Illinois “A person is not criminally responsible for conduct if
at the time of such conduct, as a result of mental disease
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Appendix to the, J.,
BREYER opinion of BREYER, J.
dissenting

State Text
or mental defect, he lacks substantial capacity to appre-
ciate the criminality of his conduct.” Ill. Comp. Stat., ch.
720, §5/6–2(a) (West 2017).
Indiana “A person is not responsible for having engaged in
prohibited conduct if, as a result of mental disease or de-
fect, he was unable to appreciate the wrongfulness of the
conduct at the time of the offense.” Ind. Code §35–41–
3–6(a) (2019).
Louisiana “If the circumstances indicate that because of a men-
tal disease or mental defect the offender was incapable
of distinguishing between right and wrong with refer-
ence to the conduct in question, the offender shall be ex-
empt from criminal responsibility.” La. Rev. Stat. Ann.
§14:14 (West 2016).
Maine “A defendant is not criminally responsible by reason
of insanity if, at the time of the criminal conduct, as a
result of mental disease or defect, the defendant lacked
substantial capacity to appreciate the wrongfulness of
the criminal conduct.” Me. Rev. Stat. Ann., Tit. 17,
§39(1) (2006).
Ohio “A person is ‘not guilty by reason of insanity’ relative
to a charge of an offense only if the person proves, in the
manner specified in section 2901.05 of the Revised Code,
that at the time of the commission of the offense, the per-
son did not know, as a result of a severe mental disease
or defect, the wrongfulness of the person’s acts.” Ohio
Rev. Code Ann. §2901.01(14) (Lexis 2014).
South “It is an affirmative defense to a prosecution for a
Carolina crime that, at the time of the commission of the act con-
stituting the offense, the defendant, as a result of mental
disease or defect, lacked the capacity to distinguish
moral or legal right from moral or legal wrong or to rec-
ognize the particular act charged as morally or legally
wrong.” S. C. Code Ann. §17–24–10(A) (2014).
South “ ‘Insanity,’ the condition of a person temporarily or
Dakota partially deprived of reason, upon proof that at the time
of committing the act, the person was incapable of know-
ing its wrongfulness, but not including an abnormality
manifested only by repeated unlawful or antisocial be-
havior.” S. D. Codified Laws §22–1–2(20) (2017).
“Insanity is an affirmative defense to a prosecution
for any criminal offense.” §22–5–10.
Texas “It is an affirmative defense to prosecution that, at the
time of the conduct charged, the actor, as a result of severe
mental disease or defect, did not know that his conduct
was wrong.” Tex. Penal Code Ann. §8.01(a) (West 2011).
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Appendix to the, J.,
BREYER dissenting
opinion of BREYER, J.

Model Penal Code
State Text
Arkansas “ ‘Lack of criminal responsibility’ means that due to a
mental disease or defect a defendant lacked the capacity
at the time of the alleged offense to either:
“(A) Appreciate the criminality of his or her conduct;
or
“(B) Conform his or her conduct to the requirements of
the law.” Ark. Code Ann. §5–2–301(6) (Supp. 2019).
Connecti- “In any prosecution for an offense, it shall be an affirm-
cut ative defense that the defendant, at the time he commit-
ted the proscribed act or acts, lacked substantial capac-
ity, as a result of mental disease or defect, either to
appreciate the wrongfulness of his conduct or to control
his conduct within the requirements of the law.” Conn.
Gen. Stat. §53a–13(a) (2017).
Hawaii “A person is not responsible, under this Code, for con-
duct if at the time of the conduct as a result of physical
or mental disease, disorder, or defect the person lacks
substantial capacity either to appreciate the wrongful-
ness of the person’s conduct or to conform the person’s
conduct to the requirements of law.” Haw. Rev. Stat.
§704–400(1) (2014).
Kentucky “A person is not responsible for criminal conduct if at
the time of such conduct, as a result of mental illness or
intellectual disability, he lacks substantial capacity either
to appreciate the criminality of his conduct or to conform
his conduct to the requirements of law.” Ky. Rev. Stat.
Ann. §504.020(1) (West 2016).
Maryland “A defendant is not criminally responsible for criminal
conduct if, at the time of that conduct, the defendant,
because of a mental disorder or mental retardation,
lacks substantial capacity to:
“(1) appreciate the criminality of that conduct; or
“(2) conform that conduct to the requirements of law.”
Md. Crim. Proc. Code Ann. §3–109(a) (2018).
Massachu- “1. Criminal responsibility. Where a defendant as-
setts serts a defense of lack of criminal responsibility and
there is evidence at trial that, viewed in the light most
favorable to the defendant, would permit a reasonable
finder of fact to have a reasonable doubt whether the de-
fendant was criminally responsible at the time of the of-
fense, the Commonwealth bears the burden of proving
beyond a reasonable doubt that the defendant was crim-
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Appendix to the, opinion
BREYER J., dissenting
of BREYER, J.

State Text
inally responsible. In this process, we require the Com-
monwealth to prove negatives beyond a reasonable
doubt: that the defendant did not have a mental disease
or defect at the time of the crime and, if that is not dis-
proved beyond a reasonable doubt, that no mental dis-
ease or defect caused the defendant to lack substantial
capacity either to appreciate the criminality of his con-
duct or to conform his conduct to the requirements of
law.” Commonwealth v. Lawson, 475 Mass. 806, 811, 62
N. E. 3d 22, 28 (2016) (internal quotation marks and ci-
tation omitted).
Michigan “It is an affirmative defense to a prosecution for a
criminal offense that the defendant was legally insane
when he or she committed the acts constituting the of-
fense. An individual is legally insane if, as a result of
mental illness as defined in section 400 of the mental
health code . . . that person lacks substantial capacity
either to appreciate the nature and quality or the wrong-
fulness of his or her conduct or to conform his or her con-
duct to the requirements of the law.” Mich. Comp. Laws
Ann. §768.21a(1) (West 2000).
Oregon “A person is guilty except for insanity if, as a result of a
qualifying mental disorder at the time of engaging in
criminal conduct, the person lacks substantial capacity
either to appreciate the criminality of the conduct or to
conform the conduct to the requirements of law.” Ore.
Rev. Stat. §161.295(1) (2019).
Rhode “A person is not responsible for criminal conduct if at the
Island time of such conduct, as a result of mental disease or de-
fect, his capacity either to appreciate the wrongfulness
or his conduct or to conform his conduct to the require-
ments of the law were so substantially impaired that he
cannot justly be held responsible.” State v. Carpio, 43 A.
3d 1, 12, n. 10 (R. I. 2012) (internal quotation marks
omitted).
Vermont “The test when used as a defense in criminal cases
shall be as follows:
“(1) A person is not responsible for criminal conduct if
at the time of such conduct as a result of mental disease
or defect he or she lacks adequate capacity either to ap-
preciate the criminality of his or her conduct or to con-
form his or her conduct to the requirements of law.” Vt.
Stat. Ann., Tit. 13, §4801(a) (2019).
West “When a defendant in a criminal case raises the issue of
Virginia insanity, the test of his responsibility for his act is
whether, at the time of the commission of the act, it was
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Appendix to the, J.,
BREYER opinion of BREYER, J.
dissenting

State Text
the result of a mental disease or defect causing the
accused to lack the capacity either to appreciate the
wrongfulness of his act or to conform his act to the re-
quirements of the law.” State v. Fleming, 237 W. Va. 44,
52–53, 784 S. E. 2d 743, 751–752 (2016).
Wisconsin “A person is not responsible for criminal conduct if at the
time of such conduct as a result of mental disease or de-
fect the person lacked substantial capacity either to ap-
preciate the wrongfulness of his or her conduct or con-
form his or her conduct to the requirements of law.” Wis.
Stat. §971.15(1) (2016).
Wyoming “A person is not responsible for criminal conduct if at
the time of the criminal conduct, as a result of mental
illness or deficiency, he lacked substantial capacity ei-
ther to appreciate the wrongfulness of his conduct or to
conform his conduct to the requirements of law.” Wyo.
Stat. Ann. §7–11–304(a) (2019).
District of “A person is not responsible for criminal conduct if at the
Columbia time of such conduct as a result of a mental disease or
defect he lacked substantial capacity either to recognize
the wrongfulness of his conduct or to conform his con-
duct to the requirements of the law.” Bethea v. United
States, 365 A. 2d 64, 79, n. 30 (D. C. 1976).

Unique formulation
State Text
New “A defendant asserting an insanity defense must prove
Hampshire two elements: first, that at the time he acted, he was suf-
fering from a mental disease or defect; and, second, that
a mental disease or defect caused his actions.” State v.
Fichera, 153 N. H. 588, 593, 903 A. 2d 1030, 1034 (2006).
North “An individual is not criminally responsible for criminal
Dakota conduct if, as a result of mental disease or defect existing
at the time the conduct occurs:
“a. The individual lacks substantial capacity to com-
prehend the harmful nature or consequences of the con-
duct, or the conduct is the result of a loss or serious dis-
tortion of the individual’s capacity to recognize reality;
and
“b. It is an essential element of the crime charged that
the individual act willfully.” N. D. Cent. Code Ann.
§12.1–04.1–01(1) (2012).