Actus Reus

The second distinction illuminating the nature of actus reus is the distinction between the prima facie case for criminal liability and the defenses. The distinction is a procedural one having to do with allocation of certain burdens in an adversary system. The burdens here pertinent are two: one party or the other is given the burden of producing evidence from which a reasonable fact-finder could find in their favor, and one party or the other is given the risk of not persuading the fact-finder with her evidence. Thus, if the prosecution in a criminal case has both burdens on a certain issue, it will have a verdict directed against it if it fails to produce evidence on that issue and it will also lose if the fact-finder is undecided about which direction the evidence points on a certain issue.

The prima facie case in a criminal trial is that part of the elements of liability on which the prosecution has both of these burdens. Actus reus is best conceived as being as much of the prohibited action as is part of the prima facie case, but no more. Specifically what is excluded by this way of conceptualizing actus reus are the justificatory defenses (Moore, 1993).

Consider homicide again by way of example. Criminal codes do not in fact prohibit simply the "killing of a human being." Rather, they prohibit the killing of a human being except in self-defense, defense of others, prevention of certain crimes, in cases of necessity, and so on. Built into the seemingly simple prohibitions of the criminal law are those exceptional circumstances where the act in question is permitted or encouraged by the law. The actus reus of murder nonetheless remains the exceptionless, simple prohibition against killing a human being, for it is only this much that the prosecution must sustain as part of its prima facie case. The defense has the burden of raising self-defense and the other justificatory defenses, so the absence of any justification of self-defense and the like is not part of the actus reus of murder.

A parallel limitation exists for mens rea. Certain defenses such as infancy, insanity, involuntary intoxication, duress, and provocation are not justificatory defenses; rather they only excuse prima facie illegal conduct. Some have urged an expansive definition of mens rea, so as to include absence of these excusing conditions as part of a "guilty mind." Preferable is the narrower conception of mens rea, paralleling the narrower conception of actus reus (Kadish). On this narrower conception, mens rea is present whenever the accused intends, believes, or unreasonably risks a prohibited action; such mens rea makes for a prima facie liability only, however, since such liability can be escaped by showing excusing circumstances in which the mental state arose.

It is controversial whether this second distinction in the criminal law reflects any underlying moral structure. On its face, the distinction is seemingly based only on the procedural convenience of dividing up the burdens of producing a trial between prosecution and defense in an adversarial system. On this view, the distinctions between actus reus and justification, and between mens rea and excuse, are morally arbitrary. That the actus reus of rape, for example, includes lack of victim consent, whereas the actus reus of criminal assault makes consent of the victim a defense (and thus not part of the actus reus), illustrates this apparent moral arbitrariness.

On the other hand, on some views of ethics morality consists of simple, exceptionless "absolutes" like "Thou shalt not kill." In this view of morality the justifications make actions permissible that are otherwise categorically prohibited. On this view one is morally permitted to kill in self-defense, for example, but it would be better if one did not take advantage of such permission (Moore, 1993). On this "stained permissions" view of the justifications like self-defense, the legal distinction between actus reus and the justificatory defenses reflects the underlying moral distinction between the categorical norms of obligation and the secondary norms of discretionary permissions. In such a view of morality the legal distinction between the actus reus of offenses and the justificatory defenses is not a morally arbitrary matter of procedural convenience.

Whatever may be the case about the moral basis for the two distinctions we have discussed, legally it is clear that actus reus is thus but one of four major elements in criminal liability. It joins mens rea, absence of justification, and absence of excuse as the four prerequisites for liability to punishment in the criminal law, and it joins mens rea in constituting the prima facie case for that liability.