M'Naghten Rule

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M'Naghten Rule

A test applied to determine whether a person accused of a crime was sane at the time of its commission and, therefore, criminally responsible for the wrongdoing.

The M'Naghten rule is a test for criminal insanity. Under the M'Naghten rule, a criminal defendant is not guilty by reason of insanity if, at the time of the alleged criminal act, the defendant was so deranged that she did not know the nature or quality of her actions or, if she knew the nature and quality of her actions, she was so deranged that she did not know that what she was doing was wrong.

The M'Naghten rule on criminal insanity is named for Daniel M'Naghten, who, in 1843, tried to kill England's prime minister Sir Robert Peel. M'Naghten thought Peel wanted to kill him, so he tried to shoot Peel but instead shot and killed Peel's secretary, Edward Drummond. Medical experts testified that M'Naghten was psychotic, and M'Naghten was found not guilty by reason of insanity.

The public chafed at the verdict, and the House of Lords in Parliament ordered the Lords of Justice of the Queen's Bench to fashion a strict definition of criminal insanity. The Lords of Justice complied and declared that insanity was a defense to criminal charges only if

at the time of the committing of the act, the party accused was labouring under such a defect of reason, from a 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. (Queen v. M'Naghten, 8 Eng. Rep. 718 [1843])

The aim of the M'Naghten rule was to limit the Insanity Defense to cognitive insanity, a basic inability to distinguish right from wrong. Other tests formulated by legislatures and courts since M'Naghten have supplemented the M'Naghten rule with another form of insanity called volitional insanity. Volitional insanity is experienced by mentally healthy persons who, although they know what they are doing is wrong, are so mentally unbalanced at the time of the criminal act that they are unable to conform their actions to the law. The M'Naghten rule was adopted in most jurisdictions in the United States, but legislatures and courts eventually modified and expanded the definition. The definition of criminal insanity now varies from jurisdiction to jurisdiction, but most of them have been influenced by the M'Naghten rule.

Many jurisdictions reject volitional insanity but retain cognitive insanity with a minor variation on the M'Naghten definition. Under the M'Naghten rule, a person was legally insane if she was so deranged that she did not know what she was doing. Under many current statutes, a person is legally insane if she is so deranged that she lacks substantial capacity to appreciate the criminality of her conduct.

The difference between the two definitions is largely theoretical. In theory, the latter definition is more lenient because it requires only that a person lack substantial capacity to appreciate her conduct.

Further readings

Kaplan, John, and Robert Weisberg. 1991. Criminal Law: Cases and Materials. 2d ed. Boston: Little, Brown.


Durham Rule; Insanity Defense.

West's Encyclopedia of American Law, edition 2. Copyright 2008 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
(22) M'Naghten Rules Definition, Duhaim's Law Dictionary,
required by the full M'Naghten rules. They knew they were preparing
For PTSD sufferers whose crimes occurred during a dissociative reaction, this second prong may be slightly preferable to the narrower M'Naghten rule, simply because it provides a jury with an alternative way to find the defendant insane.
Unlike the M'Naghten rule, the Arizona standard makes no explicit provision for a defendant who, because of a mental defect, did not "know the nature and quality" of his act.
Despite the long pedigree of the M'Naghten rule in both Britain and the United States, Souter said that ''the insanity rule, like the conceptualization of criminal offenses, is substantially open to state choice.''
[section] 17, (175) resulted in a substantial narrowing of the insanity defense in the federal criminal system, largely resurrecting the M'Naghten Rule from 1843.
In the wake of the acquittal of John Hinckley, President Reagan's attempted assassin, the legal tide turned against Durham and the M'Naghten rule came back into vogue.
1843), discussed in Simon, supra note 91, at 8 (noting that "[u]nder the M'Naghten rule the defendant is excused only if he did not know what he was doing or did not know that what he was doing was wrong").
Self-defense acknowledges that the crime occurred, i.e., the defendant committed the act, but further acknowledges that in some way the defendant's behavior was excused because his actions were justified.(22) A successful insanity plea acknowledges that the criminal act occurred, but the insanity defense holds that the accused is not criminally responsible due to his mental state.(23) There are several different legal tests to determine when and whether the insanity defense should apply including the M'Naghten rule,(24) the "irresistible impulse" test,(25) the Durham "product" test,(26) and the American Law Institute (ALI) "substantial capacity" test.(27) The ALI test is most commonly employed to determine insanity.(28)
(136) See infra note 139 (discussing the M'Naghten rule).
Thus the birth of the M'Naghten Rule in England, which is followed in a number of our states.(14) (Some states have abandoned the M'Naghten rule for the "irresistible impulse" rule - an individual is not criminally responsible if he cannot control his conduct in committing a crime even though he knows it to be wrong.