R v M’Naghten (M'Naughten) [1843] 10 Cl & Fin 2000

• Defendant shot and killed Victim while insane and the HL had to answer whether insanity was a defence.

• They said that it was.

LCJ Tindall

• Said:

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 as 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 question is to be left to the jury and the burden of evidence is on the defence.

• Also, where Defendant is insane so as to misunderstand the circumstances but is otherwise fine, the court will judge him according to the circumstances as he believed them to be:

  • E.g. if Defendant insanely believes that Victim is trying to kill him and Defendant kills Victim in self-defence he is not liable.

  • If Defendant insanely believes that Victim has insulted him and therefore kills him, then he is liable.

Maule (NB Dissenting)

• Said that such a defence couldn’t be created without Parliament’s approval. 

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