Encyclopedia of Psychology and Law

figure). Enraged by the jury’s insanity verdict, Queen

Victoria questioned why the law was of no avail, since

“everybody is morally convinced that [the] malefac-

tor...[was] perfectly conscious and aware of what he

did,” and demanded that the legislature “lay down the

rule” so as to protect the public “from the wrath of mad-

men who they feared could now kill with impunity.”

In response to the Queen’s demand, the House of

Lords asked the Supreme Court of Judicature to

answer five questions regarding the insanity law; the

judges’ answers to two of these five became the

M’Naghten test (1843):

The jurors ought to be told in all cases that every man

is presumed to be sane, and to possess a sufficient

degree of reason to be responsible for his crimes,

until the contrary be proved to their satisfaction; and

that to establish a defence on the ground of insanity,

it must be clearly proved that, at the time of the com-

mitting of the act, the party accused was labouring

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 he was doing what was wrong.

There are three main features of this formulation:

First, it is predicated on proof that the defendant was

suffering from a “defect of reason, from disease of the

mind.” From the time of M’Naghtenuntil today some

finding of “mental disease or defect” has been a neces-

sary predicate for the insanity defense. Second, once

such a “disease” is shown, the inquiry focuses on what

the defendant was able to “know.” That is, the interest

of the law under this test is in the ability of the defen-

dant to “know” certain things. It is for this reason that

the inquiry is sometimes referred to as a “cognitive”

formula. Third, the M’Naghten test focuses on two

things the defendant must be able to “know” to be

guilty of a crime. One is “the nature and quality” of the

act that was committed. The other is that the act “was

wrong.” In both instances, the question is whether the

defendant was “capable” of knowing these things, that

is, whether the mental illness had robbed the defendant

of the capacity to know what “normal” people are able

to know about their behavior. The idea, in sum, is that

people who are unable to know the nature of their con-

duct or who are unable to know that their conduct is

wrong are not proper subjects for criminal punishment.

In commonsense terms, such persons should not be

regarded as morally responsible for their behavior.

This test has been severely criticized as rigid and

inflexible, based on outmoded views of the human

psyche, of little relation to the truths of mental life,

reflecting antiquated and outworn medical and ethical

concepts. Furthermore, the use of language such as

“know” and “wrong” was criticized as “ambiguous,

obscure, unintelligible, and too narrow.” Donald

Hermann and a colleague have argued, by way of

example, that the cognitive aspect of one’s personality

cannot be seen as the sole determinant of one’s subse-

quent behavior (and the basis of one’s ultimate criminal

guilt) because the psyche is an integrated entity.

Critics also maintain that the narrow scope of the

expert testimony required by the M’Naghten test

deprives the jury of a complete picture of the psycho-

logical profile of the defendant as the test ignores

issues of affect and control.

Nevertheless, American courts readily adopted the

M’Naghten formulation and codified it as the standard

test, “with little modification,” in virtually all jurisdic-

tions until the middle of the 20th century.

Irresistible Impulse

In a partial response to criticisms of the M’Naghten test,

several courts developed an alternative test that later

became known as the “irresistible impulse” test, adapted

from a test first formulated in 1883 by Lord Stephen:

If it is not, it ought to be the law of England that no

act is a crime if the person who does it is at the

time...prevented either by defective mental power

or by any disease affecting his mind from controlling

his own conduct, unless the absence of the power of

control has been produced by his own default.

This rule allowed for the acquittal of a defendant if

his mental disorder caused him to experience an “irre-

sistible and uncontrollable impulse to commit the

offense, even if he remained able to understand the

nature of the offense and its wrongfulness.” It was

based, in the words of Abraham Goldstein, one of the

leading legal scholars on the history of the insanity

defense, on four assumptions:

First, that there are mental diseases which impair voli-

tion or self-control, even while cognition remains rela-

tively unimpaired; second, that the use of M’Naghten

alone results in findings that persons suffering from

such diseases are not insane; third, that the law should

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