Editing M'Naghten rules (section)

==Historical development==
[[File:Daniel McNaughton, Insane Murderer, in Illus. Lond. News. Wellcome L0000720.jpg|thumb|upright|A portrait of Daniel M'Naughten. Illustration for ''[[The Illustrated London News]]'', 4 February 1843]]
There are various justifications for the exemption of the insane from criminal responsibility. When mental incapacity is successfully raised as a [[defense (legal)|defence]] in a criminal trial it absolves a defendant from liability: it applies [[public policy (law)|public policies]] in relation to criminal responsibility by applying a rationale of [[compassion]], accepting that it is [[morality|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 mentally ill by the state may undermine public confidence in the penal system. A [[utilitarian]] and humanitarian approach suggests that the interests of society are better served by treatment.

Historically, insanity was seen as grounds for leniency. In pre-Norman times in England there was no distinct criminal code&nbsp;– a murderer could [[Weregild|pay compensation to the victim's family]] under the principle of "buy off the spear or bear it". The insane person's family were expected to pay any compensation for the crime. In Norman times, insanity was not seen as a defence in itself, but a special circumstance in which the jury would deliver a guilty verdict and refer the defendant to the King for a pardon<ref>Walker, N. (1968). Crime and Insanity in England:The Historical Perspective. vol.1, Edinburgh University Press; Stephen, History of Criminal Law, 151; 2 Pollock & Maitland, History of English Law, 480</ref>

<blockquote>since they are without sense and reason and can no more commit a tort or a felony than a brute animal, since they are not far removed from brutes, as is evident in the case of a minor, for if he should kill another while under age he would not suffer judgment.<ref>Bracton ''On the Laws and Customs of England'' [https://archive.today/20120710153335/http://hlsl5.law.harvard.edu/bracton/ II.424.24–27 (1210)]</ref></blockquote>

In ''R v Arnold'' 1724 16 How St. Tr. 765, the test for insanity was expressed in the following terms
<blockquote>
whether the accused is totally deprived of his understanding and memory and knew what he was doing "no more than a wild beast or a brute, or an infant".</blockquote>

The next major advance occurred in ''[[James Hadfield|Hadfield's Trial]]'' 1800 27 How St. Tr. 765, in which the court decided that a crime committed under some delusion would be excused, only if it would have been excusable had the delusion been true. This would deal with the situation, for example, when the accused imagines he is cutting through a loaf of bread, whereas in fact he is cutting through a person's neck.

Each jurisdiction may have its own standards of the insanity defence. More than one standard can be applied to any case based on multiple jurisdictions.