M'Naghten Rules - Historical Development

Historical Development

There are various justifications of the exemption from criminal responsibility of the insane. Today, mental incapacity as a defense, when successfully raised, absolves a defendant in a criminal trial from liability, that is to say it applies public policies in relation to criminal responsibility by applying a rationale of compassion, accepting that it is morally wrong to subject a person to punishment if that person is deprived permanently or temporarily of the capacity to form a necessary mental intent that the definition of a crime requires. Indeed, punishment of the obviously mentally ill by the state may act so as to undermine public confidence in the penal system. Thus, in such cases, a utilitarian and humanitarian approach suggests that the interests of society are better served by treatment of the illness rather than punishment of the individual.

Historically, insanity was initially seen as grounds for leniency. In pre-Norman times in England there was no distinct criminal code - a murderer could 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 and look after. 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

...eo quod sensu carent et ratione, non magis quam brutum animal iniuriam facere possunt nec feloniam, cum non multum distent a brutis, secundum quod videri poterit in minore, qui si alium interficeret in minori ætate, iudicium non sustineret.

...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.

In R v Arnold 1724 16 How St. Tr. 765, the test for insanity was expressed in the following terms

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".

This is clearly, by modern legal and medical standards, a simplistic test.

The next major advance occurred in Hadfield's Trial 1800 27 How St. Tr. 765 in which the court decided that a crime committed under some delusion would only be excused 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.

Nevertheless, each jurisdiction, dependant on the location, including local, state, and federal localities and jurisdiction have differing standards of the insanity defense. More than one standard can be applied to any case based on multiple jurisdictions and numerous other factors in relation to complex state and federal law; dependant on which jurisdiction and country one is in.