Justifications for the insanity defence in Great Britain and the United States: the conflicting rationales of morality and compassion.

The law of excuses is a deeply entrenched concept in Anglo-American jurisprudence which has persisted since the Middle Ages.' The excusing conditions of necessity, mistake, duress and diminished mental capacity all embrace the unitary principle that a person is not culpable, and cannot be held criminally responsible, if he had no control over his behavior.~ All the excusing conditions, then, involve a state of involuntariness. They are jurisprudential reflections of the intuitive moral statement, "I couldn't help myself." An excuse is based on the assumption that the actor's behavior is damaging and is to be deplored, but external or internal conditions which influence the act deprive the actor of choice; this negates or mitigates penal liability.; Diminished mental capacity is the most personal of all excuses. It is difficult for us to accept because it says nothing about the performance of the act itself and its attendant circumstances. Rather, it is justified by the state of awareness and cognition of the actor. The determination is whether the actor had sufficient inner understanding of the act and its consequences to justify holding him responsible. The excuse is thus inherently more difficult to observe or to reliably identify. I Diminished mental capacity may result from factors which originate outside of the body, such as with intoxication, or with automatism induced by a blow on the head, a bee sting or an emotional shock. This form of impaired cognitive volition is comparable to other excusing conditions; to the extent that the incapacity originates from outside the boundaries of the actor, it is subject to observation and, for limited purposes, can be measured. Other forms of diminished mental capacity are caused by physiological responses of the body which physically deprive the actor of choice. These physiological phenomena have an identifiable etiology and symptomatology for example, automatism induced by an epileptic seizure, a sneezing fit or a hypoglycemic episode. Science can explain such autonomic reactions and can validly identify the physical cause of volitional impairment. An excuse based on insanity, however, has a unique combination of factors none of which are subject to observation or validation: the justification for the excuse originates and remains wholly within the charac-