McNaghten’s Rules / McNaughten’s Rules / M’Naghten’s Rules of Insanity

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The defence of insanity is governed by McNaughten’s rules (M’Naghten’s case 1843).

The jurors ought to be told in all cases that every man is to be presumed to be sane, and to possess a sufficient degreee of reason to be held responsible for his crimes, until the contrary be proved to their satisfaction; and that to establish a defence on the ground of insanity, it must be clearly proved that, at the time of committing 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.


Expert Psychiatric Evidence by Keith Rix
Rix, K. (2011). Expert psychiatric evidence. RCPsych Publications.