Actus Reus

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 reus—oriented 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.