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Actus Reus


Actus reus is a term of art in criminal law. Literally the Latin phrase means bad act. The technical, legal use of the phrase denotes one of the elements that must be proven by the prosecution before anyone can be liable to criminal punishment. The actus reus element is the act made criminal by some statute or other valid source of criminal law. Thus, a defendant is said to have committed the actus reus of some offense if he has done some act that is an instance of the type of action prohibited by the offense in question. Murder statutes, for example, typically prohibit the "killing of a human being"; the actus reus of murder is satisfied by any act that is an instance of the type of act so describedthat is, any act that is a killing of a human being.

Actus reus versus mens rea

There are two contrasts with other elements of criminal liability that help to clarify the nature of actus reus. The first is the contrast with mens rea. Mens rea literally translated from the Latin means guilty mind. The technical legal use of the phrase denotes that prerequisite of criminal liability having to do with the state of mind of the accused when he committed the actus reus of some offense. Thus, one of the mens reas sufficient for murder is general intent: such requirement is often stated as a prohibition on "intentionally killing another human being." The word "intentionally" tells us what kind of mental state an accused must have to be guilty of this kind of murder (either an intent or a belief, as it turns out). The phrase "killing another human being" tells us two things: first, what must be done by way of action to be guilty of murder; and second, what object an accused's intention or belief must take in order to be guilty of murder (Moore, 1993). The first is the actus reus requirement, whereas the second is part of the mens rea requirement. The accused must both actually kill someone, and intend (or believe) that he is killing someone, in order to be guilty of this kind of murder.

The relationship between actus reus and mens rea is not always this close in all offenses. In what are often called specific intent offenses, for example, the object of the prohibited mens rea will not coincide with the act prohibited by law. Thus, the actus reus of common law burglary is the breaking and entering of the dwelling house of another at night, whereas the mens rea includes the requirement that the accused do such breaking and entering with the intent to commit a felony once inside. The commission of such a further felony is no part of the actus reus of burglary, but the intent to commit such a further felony is part of the mens rea of burglary.

In its actus reus/mens rea distinction the criminal law has mirrored a deep divide in morality. This is the divide between wrongdoing and culpability. Although it is disputed, morality is most often thought to contain certain prohibitions and requirements, such as "Do not kill" and "Help others in distress." Morality generally permits us either to do or to refrain from doing most acts, but morality forbids certain actions and requires others. To do an act morality forbids, or to refrain from doing an act morality requires, is to breach one's moral obligations. This is moral wrongdoing.

Morality likewise concerns itself with the culpability with which a wrongful act is done. Overall moral blameworthiness includes culpability as well as wrongdoing. One is free from moral blame for causing a harm to another if one neither intended to cause such a harm, believed one's act could result in such a harm, or unreasonably risked such a harm coming about because of one's actions.

The legal distinction between actus reus and mens rea is best seen as a reflection of this underlying moral distinction. The parallel is one of form, with criminal law and morality dividing criminal liability and moral responsibility (respectively) into these two elements. The difference, of course, lies in the content of legal versus moral norms; in many legal systems much that morality prohibits or requires the law does not, and vice versa.

Actus reus versus justificatory defenses

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.

The voluntary act principle

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 windowin 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. 7374). 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 actionsall of them, not just the ones used in criminal codesare 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 alland thus, an action prohibited by the criminal codethere must be a willed bodily movement.

Common criticisms of the voluntary act principle

Critics of the classic analysis of actus reus are legion. Such critics attack all four aspects of the voluntary act principle, sometimes construing it as a creature of legal doctrine and other times taking it to be a general metaphysical truth about human actions. First, it is urged, there are criminal prohibitions of states and not only of events. In Samuel Butler's fictional Erewhon one could be punished for having tuberculosis, but even in Anglo-American criminal codes one can be punished for vagrancy, possession of various items (drugs, firearms, burglary tools, etc.), being in a vehicle where marijuana is smoked, and so on.

It is sometimes said that crimes of status are compatible with the voluntary act principle because acts may "consist of a state of affairs, rather than an event" (Gross, p. 60). This, however, is to obliterate the voluntary act requirement. Voluntary acts are essentially events and if crimes of status truly exist they contradict the voluntary act principle. Better is the response of the late Herbert Packer, who noted that crimes of status "are in fact very much on the way out" (Packer, p. 78). Not only are such laws rarely enacted today, but in America a number of constitutional infirmities are regularly found to afflict such laws so that even where they do remain on the books they are not valid (Robinson v. California ).

An exception to this last observation must be made for possession crimes, which are both numerous and constitutionally valid. Such crimes seemingly prohibit the state of possessing something (weapons, drugs, etc.) and thus seem to be incompatible with the voluntary act principle. Yet possession has become a term of art in Anglo-American criminal law. Although in ordinary English and in the law of property one might easily be said to possess something simply by being in the state of having it on one's person, criminal law requires more. "Possession" is defined in criminal law so that either an act of acquiring possession or an omission to rid oneself of possession are prerequisites to liability (Williams, 1961; Model Penal Code, § 2.01(4)). With "possession" so defined, possession crimes present no counter-examples to the voluntary act principle, or at least none greater than that presented by omissions generally (which we shall shortly discuss).

A second basis for denying that the voluntary act principle is part of the actus reus requirement stems from the supposed existence of criminal actions without any bodily movements on the part of the "actor." Sometimes this objection is cast as an observation about Anglo-American criminal law: certain crimes punish culpable mental acts alone without any execution into bodily movement. More often this objection is cast as a metaphysical observation about action: some actions can be done without any bodily movement.

The legal branch of the objection would be cogent if Anglo-American criminal law still punished thoughts alone, as in the ancient form of treason constituted by the mere "compassing the death of the king" (Williams, 1961; Fletcher, 1978). Yet modern statutes require execution of the most evil thought in bodily movement. This is true not only of treason, but also of attempt, solicitation, and conspiracy as well. Unlike the Romans, we have no crimes consisting only of mental events like dreaming of the death of the emperor (Scholz).

The metaphysical branch of the objection is more complicated. The objection is that one can literally do actions like killing without lifting a finger (Fletcher, 1995; Corrado; Annas; Brand). There are three sorts of examples here: (1) the actor ("A") pushes the victim ("V") into the water, and then stands still while V drowns; (2) A is attached to a device that will kill V if, but only if, A can stand on his head motionless for ten minutes, which A does, causing V's death; (3) A is driving when suddenly his old enemy, V, darts in front of his car, and A rather than swerving, remains motionless while his car runs over V, killing him.

In fact none of these sorts of cases present examples where A has killed V without a willed bodily movement by A. About (1), A's pushing V into the water is a voluntary act that caused V's death so that A did kill V, but not without moving his body. About (2), A again did kill V, but he again moved his body to do so. The trick is to see that A's activating the muscles needed to remain motionless are bodily movements too. For difficult routines where the "agent's body is about to be made to move by outside forces," to keep one's exterior body from moving by activating the appropriate muscles is to engage in willed bodily movement in the sense intended by the voluntary act principle (Vermazen, p. 95; see also Holmes; Moore, 1993, 1994). About (3), A does not kill V with his car. A will doubtlessly be liable for V's death, but not because A killed V; rather, A omitted to save V when A was duty-bound to do so because A's earlier acts of driving put V in danger (Moore, 1994). None of these examples disprove the voluntary act principle by producing instances of "motionless killings."

A third objection to the voluntary act principle stems from that principle's reliance on willings to mark the line between voluntary and involuntary bodily movements. The objection is that there are many voluntary actions where there is no datable mental state of willing. While this objection once had many adherents in both law (Hart) and philosophy (Ryle), more recent analyses have sustained the need for some state like willing, volition, endeavoring, intent to move, and so forth, to mark off voluntary action from mere involuntary movement (Moore, 1993, 1994; Bratman).

A fourth objection to the voluntary act principle disagrees with that principle's fourth thesis. Such an objection denies that the death I cause by shooting another is no proper part of my act. On this view my killing, my shooting, my pulling of the trigger, and my moving my trigger finger, are each distinct particular acts I did, not just four different descriptions of one act I did. On this view my act of killing is distinct from my act of moving my trigger finger, even though I did the former by doing the latter. The objection concludes that acts like killing others do not have at their core willed bodily movements or anything else. A killing is a killing, a burning is a burning, but they need share no feature universal to all actions, as is asserted to be the case by the voluntary act principle.

While there is a surprising amount to be said in favor of this objection (Goldman, 1970, 1994), common sense supports the voluntary act principle. When I move my trigger finger, when I move it slowly, when I move it smoothly, when I pull the trigger by moving it, and so on, I am doing one act, not as many acts as there are descriptions of it (Moore, 1993). Such a chain of descriptions of but a single act leaves open the possibility asserted to be true by the voluntary act principle: all actions are essentially willed bodily movements.

We have thus far deferred any discussion of omissions because they present the most serious objection to the view that the actus reus of all offenses includes a voluntary act. The objection also is a complicated one because those who voice it do not even agree what omissions are. The best conceptualization of omissions is that they are simply absent actions. An omission by actor A to save V from drowning is just the absence of any act by A of saving V. Such omission is not a ghostly act of saving or of anything else; rather, it is the absence of any such type of act. Such omissions are thus a kind of action no more than nonexistent elephants are a kind of elephant (Moore, 1993).

The voluntary act principle states that all actions are in essence willed bodily movements. An omission to save V at some time t thus might consist in A not moving his body at t. Yet motionless omitters are rare. Usually one who omits to save is busy doing something else at tdancing a jig, buying a dishwasher, and so forth. What makes such persons omitters to save at time t is that none of their willed bodily movements at t has the causal property, saving-of-V's-life. One thus does not want to picture omitters as motionless statues because they need not be such (and they typically are not such).

Once we are clear as to what omissions are, we can see that Anglo-American law undeniably criminalizes some omissions. If we are the parent of a child who needs rescue, if we have undertaken such rescue even if we are not related to the child, if we have either innocently or culpably caused the condition of peril to the child, or if some statute specifically imposes a duty on us to rescue the child, we are under a positive legal duty to prevent the child's death. Despite numerous efforts to reconcile this liability with the voluntary act principle (Hughes; Gross; Epstein; Mack), the simple truth is that they are not reconcilable (Moore, 1993). Insofar as Anglo-American law criminalizes true omissions, it creates an exception to the principle that a willed bodily movement constitutes the essence of the actus reus of all criminal offenses. The voluntary act principle remains of great importance, however, because omission liability is rare in Anglo-American law and thus almost all the time it remains true that the actus reus requirement can be satisfied only by a willed bodily movement.

For the exceptional cases of omission liability we do need an account paralleling the voluntary act principle's account for act liability. If the essence of criminal omissions is not willed bodily movements, what might it be? Some have suggested that the essence of omissions is also to be found in willing. The analysis is that omissions are the willed absence of bodily movements (Fletcher, 1994). In this way one keeps as close a parallel to the voluntary act principle as possible. Yet willed absences of bodily movements is too narrow an analysis of omissions generically and it is even too narrow as an analysis of omissions made criminal by Anglo-American codes. If I negligently do not notice the child in distress, I negligently omit to save her. This is an omission, and if I am the child's parent, a criminal omission, yet I at no point willed the nonmovement of my limbs to refrain from saving her (Bentham).

The preferable line to take here is to see that the omissions we criminalize all have as their common element a capacity of the omitter not to have omitted. If I am to be held criminally liable for omitting to save my child, I must at a minimum have had the capacity to move my limbs in the relevant wayI was not asleep, in the middle of an epileptic seizure, under hypnosis, paralyzed, and so on, at the relevant times. Then I can be said to have voluntarily omitted to rescue the child.

This completes one-half of the analysis of actus reus in the criminal law. At a minimum, to satisfy the actus reus requirement of some offense one must satisfy the voluntary act principle (or in exceptional cases, the voluntary omission principle). We now need to see what else must be true in order to satisfy the actus reus requirement for criminal liability.

The properties common to complex types of actions

If criminal codes only prohibited actions like moving one's finger, then the actus reus requirement would be exhausted by the voluntary act principle. Yet for obvious reasons no criminal code consists exclusively (or even in part) of such prohibitions. We are morally and legally indifferent to such simple actions so no one has any reason to criminalize them. Rather, we criminalize more complex actions like killing another, destroying property, raping, maiming, and stealing. What else is true about all of these types of actions (beyond the fact that all are in essence willed bodily movements)?

What we seek here are useful generalizations about properties possessed by the thousands of actions prohibited by our criminal codes. It has been traditional to group all such properties into only two types: causal properties and noncausal properties of actions (Bentham; Austin; Williams; Model Penal Code § 1.13(9)). Killings of a human being, for example, are willed bodily movements having the causing of death of a human being as a property. The death is then said to be the result element of the actus reus of homicide. Death is so described because death of a human being must be the result of any willed bodily movement that is a killing of (i.e., a causing the death of) a human being. Killings of a police officer while in the performance of her official duties, by contrast, are willed bodily movements having not only the causal property of all killings but also having the noncausal properties that the person killed was a police officer and was on duty at the time. The facts that the victim was a police officer and that the victim was on duty at the time of the killing are then said to be the circumstance elements of the actus reus of cop-killing. These facts are described as "circumstances" because they are not caused by the defendant's willed bodily movement; they are simply facts ("circumstances") present at the time the defendant acted.

The criminal law's division of all properties of actions into these two kinds is uniquely legal. There is no corresponding division of the properties actions may possess in either philosophy or in ordinary thought. Philosophers of action often distinguish the properties actions may possess quite differently. Such philosophers often speak of causal properties, as do criminal lawyers, but noncausal properties are often divided up into conventional properties, mental properties, properties of the agent, properties of the victim, properties having to do with the manner, means, or instrumentality used, and so on (Rescher; Goldman; Bennet; Thalberg).

It is thus important to be clear why the criminal law is categorizing the properties actions may possess in order to assess the adequacy of its analysis. Perhaps surprisingly, the criminal law has little actus reusoriented purpose in classifying the properties possessed by those actions criminal law prohibits. For we can determine whether a defendant satisfies the actus reus requirement for any crime without classifying the properties of action; we only need ascertain whether the act of the accused has the various properties each crime requires. Thus, the justification for classifying the properties of actions lies elsewhere, in the need of the criminal law to draw certain mens rea distinctions. These mens rea distinctions are between one who intends to cause a certain harm, one who knows to a practical certainty that his action will cause that harm, one who knows that his action will substantially and unjustifiably risk that harm, and one who unreasonably risks causing that harm even though he is unaware of that risk. These distinctions are used by the criminal law to grade the culpability with which a given wrongful act is done. The unaware but unreasonable risker is least culpable, and the intender is most culpable, with the knowing and reckless causers graded between these two extremes.

Such a grading scheme for culpable mens reas seemingly demands that the criminal law classify all properties of prohibited actions into causal or noncausal properties. The idea is that the grading scheme above described only makes moral sense with respect to the causal properties, but not the noncausal properties, of actions. Consider the crime of assault with intent to kill a police officer performing his official duties. Such a crime requires the most seriously culpable of the mental states, namely, an intent to kill; mere belief to a practical certainty that one's actions will result in death will not satisfy the mens rea requirement of this offense. Thus, a defendant who sets off a bomb against a prison wall in order to help some prisoners escape (while knowing that the guard next to the wall will be killed by the explosion) does not have the intent to kill; whereas another defendant who sets the bomb in order to kill the guard (in order that the guard cannot later identify the defendant) has the required intent to kill.

With regard to the causal property, causing-death-of-a-human-being, use of the intent/knowledge distinction seems to work well enough. The defendant who intends to kill is somewhat more culpable than the defendant who does not so intend but who only knows that his action will result in someone's death. But now imagine two more defendants, each of whom assault an on-duty police officer with the intent to kill him. The first of this pair of defendants knows that his intended victim is a police officer and knows that he is on duty; however, his reason for wanting to kill the officer has nothing to do with these facts, for this defendant hates the cop for personal reasons. By contrast the second defendant cares whether his intended victim is a police officer and whether that victim is on duty. We may suppose that this second defendant is engaged in a cop-killing contest between lifers in prison where there is no death penalty, and one "scores" in the contest only if one kills an on-duty policeman.

Defendant two is moved to kill the person he assaults by the fact that that person is an on-duty cop; defendant one is indifferent to these facts, although he knows that they exist. Both the common law and the Model Penal Code deny there to be any significant difference in culpability between these last two defendants. If one takes this view, then we do not want to distinguish between them when we grade culpability by mental states. We should thus lump those who literally intend to kill an on-duty cop with those who intend to kill a person who happens to be an on-duty cop (and who they know to be such), treating both as guilty of the most culpable grade of mental state.

We can define this most serious grade of culpability differently only if we can divide all criminal actions into two different aspects. This is where the causal versus noncausal property distinction is needed. If the property in question is causal, then the most serious grade of culpability requires intent as its mental state; if the property in question is noncausal, then the most serious grade of culpability allows belief to a practical certainty to suffice along with intent.

Other distinctions between the mental states that grade culpability are also thought to demand this distinction between causal and noncausal properties of action (Moore, 1993). Rather than pursue these, however, we should turn to three criticisms commonly made of this classification scheme.

Criticisms of the circumstance/consequence distinction

One is a moral criticism. The argument is that there is some difference in the culpability of the last pair of would-be cop-killers, and, indeed, as much difference as there is between the first pair of prison bombers. If this is so, then our reason for categorizing all properties of actions into two large clumps disappears.

It is hard not to have considerable sympathy for this moral criticism. Nonetheless, perhaps an enriched diet of examples can tip one back toward the orthodox criminal law categorization of actions. Consider this one. Two defendants each commit an assault with intent to have intercourse with a female who they know is not consenting. Defendant one is indifferent to the fact, seeking intercourse whether the victim consents or not; defendant two only likes nonconsensual sex, so that if the victim consented he would cease his assault. If both defendants are sufficiently close in culpability as to be lumped together in the most serious grade of culpability, then the criminal law may well be correct to draw its culpability distinctions differently for the noncausal property of consent than for the causal property of penetration.

It is also not quite true that the only reason for the criminal law to draw the causal/noncausal property distinction is in order to grade culpability systematically. If these kinds of properties differ in the universality with which they apply to criminal actions, that is a fact worth marking in systematizing criminal law. Although it is controversialas we shall explore momentarilyall actions prohibited by Anglo-American criminal code have causal properties, while this is not true of noncausal properties. This is a fact worth marking, possible only if one distinguishes the two kinds of properties.

The second criticism of the causal/noncausal property classification is that it is incomplete. The argument is that certain actions are not divisible into their causal or their noncausal properties; rather such actions are said to have a nature that is neither. Such crimes are often termed "conduct" crimes, of which theft, rape, attempt, breaking and entering, and driving under the influence of alcohol are supposed to be examples.

This is a difficult criticism to get a handle on, since it seems so obviously false. Still, the criticism is a very popular one among criminal law theorists (Williams, 1983; Buxton; Fletcher, 1978), and it even infects the Model Penal Code when that Code (inconsistently) inserts "nature" of an action as an element in addition to "results" and "circumstances" (MPC § 2.02; see Moore, 1993). So the criticism must at least be taken seriously enough to be explained away as a mistake.

None of the supposed examples of "conduct crimes" turn out to require an analysis different than the orthodox analysis of action in criminal law. Take breaking and entering, for example. The actus reus of breaking and entering is breaking and entering a building not your own. That the building entered is owned by someone else is a noncausal property of the action requireda "circumstance element," in the language of the Model Penal Code (MPC § 1.13(9)). A breaking occurs when a willed bodily movement causes a window to be broken, and an entering occurs when a willed bodily movement takes place in the circumstance that an outward threshold of a building is crossed. There is no need for a nature to breaking and entering, since the actus reus of that offense is fully analyzable in the orthodox way.

The same analysis is adequate for the other supposed examples of "conduct crimes." The actus reus of rape is satisfied when a willed bodily movement causes penetration in the circumstance where there is a lack of victim consent. The actus reus of theft is satisfied when a willed bodily movement causes an item to move in the circumstances that the item in question is owned by another who has not consented to its taking. The actus reus of attempted murder is satisfied when a willed bodily movement causes a state of near success in killing to exist, and so on.

There are two apparent reasons explaining the persistence of this "conduct crimes" criticism despite its manifest falsity. One is due to the directness of the causal links between willed bodily movements and results in conduct crimes. Usually the causal chain between certain willed bodily movements and penetration in rape, for example, is very short. The shortness of the chain leads some to think that there is no causal link here at all. Yet a short causal chain is still a causal chain. In addition, once in a great while the chain is not so short, as when the defendant inserts the penis of another into the female (Commonwealth v. Dusenberry ). Such cases make plain what was true all along: There is a causal property built into the actus reus of rape and other "conduct crimes," so that no sui generis "nature" of rape needs to be added into the analysis of that actus reus.

The second reason explaining the confusion about conduct crimes lies in certain linguistic facts. When we say, "The actus reus of theft is the moving of a chattel and such action of moving involves the causing of movement by that chattel," it may seem that the causal analysis is bogus. It sounds like saying, "The action of moving something involves moving that thing," which is trivial. Unnoticed is that the English language uses "moving" and "movement" in two quite different ways. "The moving of the chattel" refers to an action, whereas "the movement of the chattel" refers to a different event, the event of the chattel moving. The latter event could be caused by an action of moving, or it might not. It is thus a significant assertion to say that "the willed bodily movement caused the movement of the chattel" and even to say, "The moving of the chattel caused the movement of the chattel." The causing of movement of a chattel is thus a causal property of moving a chattel, and no sui generis idea of "nature" need be added to analyze this action.

The third criticism of the orthodox division is that the causal/noncausal property distinction is wholly indeterminate. The potential indeterminancy appears when we consider how much to include as part of what is caused by an actor's willed bodily movements. Consider the actus reus of killing an on-duty policeman. The standard analysis is that the causing of a death of a human being is a causal property any act must possess to be an instance of this prohibited act-type, and that the victim of such killing is a police officer, and on duty, are noncausal properties any act must possess to be an instance of the prohibited act-type. Yet, why isn't causing the death of something the causal property, and the circumstance that the killed thing is a person or noncausal property? Alternatively, why isn't the causing of death of an on-duty policeman a causal property, with no noncausal property? Without some control on how we individuate propertiesa notoriously tricky business (Armstrong)it would seem that the orthodox classification scheme can be manipulated at will.

There is no dearth of suggestions as to how to deal with this problem. Some have suggested a temporal criterion: if the fact exists at the time of the willed bodily movement, then it is a noncausal property of that act. Others have urged a conventional criterion: what is "customarily regarded" as part of what is caused forms part of a causal property (Buxton, p. 31). Still others have urged a moral criterion: ask whether the intent/knowledge distinction marks any significant difference in culpability vis-à-vis the property in question, and if it does not, call the property noncausal (Moore, 1993). One might even urge a metaphysical criterion: include just so much of the state of affairs prohibited in the causal property as corresponds to true causal laws (see Armstrong). None of these suggested responses, however, has proved adequate to the objection.

Despite this unanswered criticism, the second general truth about actus reus retains wide acceptance: in addition to a willed bodily movement, the actus reus of all offenses includes the consequences of that movement and the circumstance in which that movement took place. These consequences and circumstances constitute the causal and the noncausal properties, respectively, that any willed bodily movement must possess if it is to satisfy the actus reus requirement of the criminal law.

Michael S. Moore

See also Burden of Proof; Crime: Definition; Mens Rea; Vicarious Liability.


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Commonwealth v. Dusenbery, 220 Va. 770, 263 S.E. 2d 392 (1980).

Powell v. Texas, 392 U.S. 514 (1968).

Robinson v. California, 370 U.S. 660 (1962).

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Actus Reus


[Latin, Guilty act.] As an element of criminal responsibility, the wrongful act or omission that comprises the physical components of a crime. Criminal statutes generally require proof of both actus reus and mens rea on the part of a defendant in order to establish criminal liability.

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