The M’Naghten rule — not knowing right from wrong
The rule created a presumption of sanity, unless the defense proved “at the time of committing the act, the accused was laboring 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 what he was doing was wrong.”
The Durham rule — “irresistible impulse”
Citing leading psychiatrists and jurists of the day, the appellate judge stated that the McNaughton rule was based on “an entirely obsolete and misleading conception of the nature of insanity.” He overturned Durham’s conviction and established a new rule. The Durham rule states “that an accused is not criminally responsible if his unlawful act was the product of mental disease or mental defect.” The Durham rule was eventually rejected by the federal courts, because it cast too broad a net. Alcoholics, compulsive gamblers, and drug addicts had successfully used the defense to defeat a wide variety of crimes.
In 1984, Congress passed, and President Ronald Reagan signed, the Comprehensive Crime Control Act. The federal insanity defense now requires the defendant to prove, by “clear and convincing evidence,” that “at the time of the commission of the acts constituting the offense, the defendant, as a result of a severe mental disease or defect, was unable to appreciate the nature and quality or the wrongfulness of his acts” (18 U.S.C. § 17). This is generally viewed as a return to the “knowing right from wrong” standard.
(from Cornell, LII)