Towards a more just insanity defence: recovering moral wrongfulness in the M'Naghten Rules

Abstract

This article describes how the M'Naghten Rules, which govern the law of insanity in England and Wales, came into existence. In relation to knowledge of the wrongfulness of the alleged act, the article reveals how the Court of Appeal has sought to limit the defence, whereas the courts of first instance, and a number of other jurisdictions, have adopted interpretations of the Rules that accord more closely with the law of insanity as it existed at the time of Daniel McNaughtan's trial and that the Rules were probably meant to formulate. Three cases are used to illustrate the difficulties resulting from the position adopted by the Court of Appeal. It is suggested that in cases where the insanity defence is raised, justice is likely to be better served by addressing specifically and separately the accused's understanding or appreciation of the moral wrongfulness of the alleged act and their knowledge as to whether the alleged act is contrary to the law of the land.