(mik-naw´ton) a definition of criminal responsibility formulated in 1843 by English judges questioned by the House of Lords as a result of the acquittal of Daniel M'Naghten on grounds of insanity. It holds that “to establish a defense on the ground of insanity, it must be clearly proved that, at the time of committing the act, the party 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, he did not know he was doing what was wrong” and further that a defendant who “labors under partial delusions only and is not in other respects insane..must be considered in the same situation as to responsibility as if the facts with respect to which the delusion exists were real.” These rules are still used in many American jurisdictions.