Actus Reus

Having isolated actus reus within the overall requirements for criminal liability, it remains to examine its nature. The general nature of the requirement we have stated earlier: actus reus is the requirement that the accused have performed an action prohibited, at least prima facie, by the criminal law. We gain more insight into the nature of this requirement if we probe the nature of actions themselves. If the criminal law requires actions for liability, we would do well to understand what might be generally true of human actions.

This seemingly intuitive route for analysis runs into a long-existing, widely shared skepticism that denies the existence of any general truths about human actions as such. This skepticism admits that we can seek the nature of specific kinds of actions, such as killings, maimings, destroyings, and so on. Denied is that all such types of actions have any shared nature (Austin, 1956; Duff).

If such skepticism were true then the most we could say about the actus reus requirement of the criminal law is what we have said before: actus reus is the requirement that, before one is liable to punishment, one not do one of the many thousands of actions prohibited by the criminal law. Fortunately the metaphysics of human action is not as bleak as this skepticism would contend. There are two very general truths about human actions as such (and thus, about all those many human actions prohibited by Anglo-American criminal codes).

One of those truths is encapsulated within the criminal law's so-called voluntary act principle. The voluntary act principle states that there can be no actus reus (and thus, no criminal liability) unless the defendant performed a voluntary act. A voluntary act, in turn, is defined as a bodily movement caused by the "effort or determination of the actor, either conscious or habitual" (Model Penal Code § 2.01(2)(d)). The voluntary act principle thus requires willed bodily movement by a defendant before criminal liability may attach.

To understand the voluntary act principle, it is helpful to subdivide it into four subprinciples. The first is the idea that voluntary acts are events and are not one of those more enduring things we call states. My firing of a gun yesterday is an event that occurred over a relatively brief interval of time and that involved change in the world. My being a person who likes to fire guns is a more enduring state not involving change but rather stasis.

The U.S. Supreme Court for a time attempted to articulate this distinction in its holdings prohibiting criminal punishment for status rather than action. In Robinson v. California, 370 U.S. 660 (1962), the Court held it unconstitutional for California to punish someone for the status of being an addict, recognizing that it was constitutionally permissible to punish someone for the actions of using drugs. Similarly in Powell v. Texas, 392 U.S. 514 (1968), the Court allowed the punishment of someone for being drunk in public because implicit in the actus reus of the crime was the action of going into public while one was drunk.

The second subprinciple is that voluntary actions are physical events involving the only physical mechanism within our immediate control, our own bodies. While there are mental events like deciding or intending to do something, voluntary acts are not these kinds of events. Rather, a voluntary act is (at least in part) the physical event of our bodies moving in response to our intentions to move them. The insight motivating this second aspect of the voluntary act principle is that the criminal law cares about harms in the world. The only means persons have at their disposal to bring such harms about is by use of their bodies. None of us has telekinetic powers so that only through bodily movement do our evil thoughts produce evil consequences.

The third subprinciple is that only willed bodily movements count as voluntary actions. Our bodies often "act" in the same way that inanimate objects "act," which is to say without our direction or control. If my body is thrown through a window, I cannot be said to have performed the voluntary act of breaking the window; in such cases, my body is no different than a stone that I happen to own breaking the window—in neither case have I broken the window. Similarly, if I am in the midst of an epileptic seizure, a hypogly episode, a reflex or shock reaction, hypnosis, somnambulistic or fugue state, or the like, I am not the author of the harms my body may cause. It is only bodily movements caused by my intention (or "willing") to so move that constitute voluntary actions (Moore, 1993).

Fourth and last, the results of my willed bodily movements are not proper parts of my voluntary actions nor do such results themselves constitute separate voluntary actions. John Austin stated this thesis explicitly: "a voluntary movement of my body. . .is an act. . .bodily movements are the only objects to which the term 'acts' can be applied with perfect precision and propriety" (p. 415). Oliver Wendell Holmes put this point even more succinctly: An action "is a willed muscular contraction, nothing more" (pp. 73–74). Consider the actions of killing someone by way of example. The English language suggests that we cannot kill another without causing the other's death. Are we to infer that the death of the victim, or the causing of it by one's bodily movements, are parts of the voluntary act of killing? Perhaps surprisingly, the answer is no. The only voluntary acts we do are the willed bodily movements by which we kill. What happens after that is no part of our voluntary act, nor is the death resulting a separate voluntary act we do. To paraphrase Holmes and Austin, all we ever do is move our bodies, and the rest is up to nature.

On this view, the causing of death by some bodily movement is a property of that act just as being "the most talked about killing of the decade" can be a property of an act of killing. One way to refer to the act in idiomatic English is by use of these causal properties: "The killing of Nicole," or "the most talked about killing of the decade." Yet the death of Nicole, the causing of it, the talk generated by it, are no part of the voluntary act of her killer. These descriptions are simply ways of referring to that willed bodily movement by use of familiar properties. We do the same thing when we talk of "the teacher of Alexander," referring to Aristotle. It is not an essential part of Aristotle that he taught Alexander, but use of this nonessential but familiar property is a good way to refer to him.

Lawyers and legal theorists often present the voluntary act principle as a distinctively legal principle. They often defend it as a special invention of the law, serving law's unique needs. In fact the four subtheses of the voluntary act principle simply restate some well-worn truths about human actions in metaphysics. Everything lawyers say about voluntary acts many philosophers would say about human actions generically. Human actions—all of them, not just the ones used in criminal codes—are events; they are those physical events known as bodily movements; they are only a subclass of such physical events, namely, only those bodily movements caused by an intention to so move; and the only actions there are are willed bodily movements, however much we refer to those actions via their causal properties (Davidson; Moore, 1993). The voluntary act principle should be seen for what it is, an analysis of the nature of human action as such. So seen, it is one-half of the story of what it is the actus reus principle of criminal law requires: to be an action at all—and thus, an action prohibited by the criminal code—there must be a willed bodily movement.