Court case(1843) 10 Cl & F 200

Daniel M'Naghten, suffering from the delusion that he was persecuted by the Tory party, shot and killed Edward Drummond, private secretary to the Prime Minister Sir Robert Peel, mistaking him for Peel. He was tried for murder and acquitted on the ground of insanity. The acquittal caused public alarm, and the House of Lords put a series of questions to the judges on the law of insanity.

Tindal CJ, answering for the judges, laid down the M'Naghten Rules: every man is presumed sane and responsible until the contrary is proved; to establish a defence of insanity it must be clearly proved that, at the time of committing the act, the 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 that what he was doing was wrong. A person under a partial delusion is judged as if the facts he imagined were real.