The M’Naghten rule (pronounced, and sometimes spelled, McNaughton) is any variant of the 1840s jury instruction in a criminal case when there is a defence of insanity:
that every man is to
The M’Naghten rule (pronounced, and sometimes spelled, McNaughton) is any variant of the 1840s jury instruction in a criminal case when there is a defence of insanity:
that every man is to be presumed to be sane, and … that to establish a defence on the ground of insanity, it must be clearly proved that, at the time of the committing 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.
The rule was formulated as a reaction to the acquittal in 1843 of Daniel M’Naghten on the charge of murdering Edward Drummond. M’Naghten had shot Drummond after mistakenly identifying him as UK Prime Minister Robert Peel, who was the intended target. The House of Lords asked a panel of judges, presided over by Sir Nicolas Conyngham Tindal, Chief Justice of the Common Pleas, a series of hypothetical questions about the defence of insanity. The principles expounded by this panel have come to be known as the “M’Naghten Rules”, though they have gained any status only by usage in the common law and M’Naghten himself would have been found guilty if they had been applied at his trial.
The rules so formulated as M’Naghten’s Case 1843 10 C & F 200 have been a standard test for criminal liability in relation to mentally disordered defendants in common law jurisdictions ever since, with some minor adjustments. When the tests set out by the Rules are satisfied, the accused may be adjudged “not guilty by reason of insanity” or “guilty but insane” and the sentence may be a mandatory or discretionary (but usually indeterminate) period of treatment in a secure hospital facility, or otherwise at the discretion of the court (depending on the country and the offence charged) instead of a punitive disposal.
The insanity defence is recognised in Australia, Canada, England and Wales, Hong Kong, India, the Republic of Ireland, New Zealand, Norway and most US states with the exception of Idaho, Kansas, Montana, Utah, and Vermont but not all of these jurisdictions still use the M’Naghten Rules. States that disallow the insanity defence still allow defendants to demonstrate that they are not capable of forming intent to commit a crime as a result of mental illness.
Refer to Chronology of UK Mental Health Legislation, Diminished Responsibility (in English Law), Diminished Responsibility (General), and Insanity Defence.
There are various justifications for the exemption of the insane from criminal responsibility. When mental incapacity is successfully raised as a defence in a criminal trial it absolves a defendant from liability: it applies public policies in relation to criminal responsibility by applying a rationale of compassion, accepting that it is morally wrong to punish a person if that person is deprived permanently or temporarily of the capacity to form a necessary mental intent that the definition of a crime requires. Punishment of the obviously me