McNaghten rules (mik-nawt-<<schwa>>n).Criminal law. The doctrine that a person is not criminally responsible for an act when a mental disability prevented the person from knowing either the nature and quality of the act or whether the act was right or wrong. • The federal courts and most states have adopted this test in some form. McNaghten’s Case, 8 Eng. Rep. 718 (H.L. 1843). — Also spelled McNaughten rules; M’Naghten rules; M’Naughten rules. — Also termed right-and-wrong test; right–wrong test. See INSANITY DEFENSE. [Cases: Criminal Law 48.]

“Four points stand out and should be understood whenever reference to M’Naghten is made other than in regard to procedure. (1) It applies only in case of ‘a defect of reason, from disease of the mind’ and without this the following do not apply except that ‘disease’ as so used will be interpreted to include congenital defect or traumatic injury. (2) If, because of this ‘defect of reason,’ the defendant did not know what he was doing he is not guilty of crime. (3) Even if the defendant knew what he was doing he is not guilty of crime if, because of this ‘defect of reason,’ he did not know he was doing wrong. (4) If the defendant acted under an insane delusion, and was not otherwise insane, his accountability to the criminal law is the same as if the facts were as they seemed to him to be.” Rollin M. Perkins & Ronald N. Boyce, Criminal Law 959–60 (3d ed. 1982).

[Blacks Law 8th]