Excuse: Theory

In any given legal system, researchers might encounter difficulty enumerating the recognized excuses. At a certain period of history, certain circumstances might function as an excuse; at a later period the same considerations might be conceptualized as a denial that the act itself is criminal. The fate of the common law excuses se defendendo (self-defense) and per infortunium (inevitable accident) illustrates this process. In the common law of homicide, both of these defenses generated the exemption from punishment known as "excusable homicide" (Blackstone, pp. 182–187; Cal. Penal Code § 195). Treating these claims as excuses reflected the assumption that any killing of another human being was criminal or wrongful. The excuse did not negate this wrongfulness but rather, in the idiom of civil pleading, merely "confessed" the wrong and sought to "avoid" the consequences.

Today both of these claims are treated as denials that the act is criminal. As noted above, the excuse of se defendendo has given way to the statutory justification of self-defense. The excuse of per infortunium has undergone a reconceptualization, and functions now in the form of a denial that the killing was either intentional or negligent. Because it is now assumed that a wrongful killing must be either intentional or grossly negligent, the claim of accident challenges the wrongfulness of the killing.

If these excuses have been absorbed into the analysis of wrongfulness, other claims, properly regarded as justificatory, are occasionally treated as excuses. A good example is the claim of respondeat superior, or superior orders. This claim arises if a soldier or citizen executes "an order of his superior . . . which he does not know to be unlawful" (Model Penal Code § 2.10). If the order is lawful, then presumably the execution would also be regarded as lawful. A lawful act does not raise a question of excusability. However, if the order is unlawful, the actor's ignorance of the legal quality of the order and of his execution might excuse him by analogy with mistake of law. The Model Penal Code formulation encompasses both of these variations in one provision and locates the section in its chapter devoted primarily to claims of excuse rather than justification. The implicit analogy with duress in Section 2.09 of the Code stresses the coercive, rather than the legitimating, aspect of superior military orders.

Although the distinction between claims of justification and of excuse remains defensible in principle, Anglo-American legal thought has yet to achieve consensus regarding the exact nature not only of superior orders but of duress, personal necessity, and mistake of law.