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.

References in periodicals archive ?
The M'Naghten rules state that a defendant should not be held responsible for his actions only if, due to his mental disease or defect, he did not know that his act would be wrong or did not understand the nature and quality of his actions.
The M'Naghten rules has been criticized because it is only a cognitive standard and does not have a volitional arm.
In 1962, the American Law Institute published the Model Penal Code, which combined the strictly cognitive M'Naghten rules and the irresistible impulse test.
adopted the M'Naghten rules they were simply codifying what was
delusion" part of the M'Naghten rules, so the integrationist
Clark argued that the full M'Naghten rule was the minimum test
The statistics cited above suggest that although insanity pleas were ostensibly evaluated according to the objective criteria known as the M'Naghten Rules, the insanity acquittal was gendered, and subjective notions of appropriate male and female behaviour dictated how jurors would respond to insanity pleas.
13) Named for the particularly controversial case which inspired their creation, the M'Naghten Rules stipulated that a defendant was not legally responsible for his crime if at the time he committed the crime he "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.
16) Not only did the M'Naghten Rules inspire debate between and within the legal and medical professions, but they fell far short of eliminating public doubt about the legitimacy of the insanity acquittal.
Although England did not codify the insanity test in the M'Naghten rules until 1843, various cultures have excused mentally ill individuals from criminal responsibility.
117) The M'Naghten rules require that an individual must clearly prove that "at the time of the committing of the act," he or she 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 or she was committing, and if he or she was aware, he or she "did not know" that the act was wrong.
122) Therefore, under the stricter M'Naghten rules, M'Naghten himself would most likely "be judged sane and legally culpable by the standards of the rules which bear his name.