Introductory note: This chapter examines the requirement that the defendant’s actus reus must have “caused” the harmful result. The prosecutor must make two distinct showings of causation: (1) that the act was the “cause in fact” of the harm; and (2) that the act was the “proximate” or “legal” cause of the harm. Problems like that of the unintended victim, or the intervening act, fall within category (2).
A. Causation generally: The problems of concurrence, discussed in the previous chapter, related to the links between mental state and act, and between mental state and harmful result. We turn now to the link between act and harmful result. Where the links between the defendant’s act and the harmful result that ensues are unduly tenuous, we say that there is no causal relationship between the two, and therefore no liability.
B. Two aspects of causation: In the case of any crime which is defined in terms of harmful results (e.g., murder, rape, arson etc.), the prosecution must prove that the defendant’s actus reus “caused” the harmful result. To do this the prosecution must in reality make two different showings: (1) that the act was the “cause in fact” of the harm; and (2) that the act was the “proximate” cause (or, as the Model Penal Code puts it, the “legal” cause) of the harm. We consider each of these aspects in turn.
A. Cause in fact generally: For an act to be a “cause in fact” of a result, it is often said that it must be the “but for” antecedent of that result. By this is meant that if the result would have happened anyway, even had the act not occurred, the act is not a cause in fact of that result.
Example: D shoots at V, but only grazes him, leaving V with a slightly-bleeding flesh wound. X then comes along and shoots V through the heart, killing him instantly. D’s act is clearly not a “cause in fact” of V’s death, since V would have died, and in just the manner he did, even if D had not shot him.
1. Expansive test: This “but for” test is obviously a very expansive one, under which every result will have literally thousands of antecedent “but for” causes in fact. In the above example, for instance, X’s act is obviously a cause in fact of V’s death, since he would not have died when he did without that act. But the act of the weapons’ manufacturer in making X’s gun was also a “but for” cause, since if X had not had the gun, he couldn’t have shot V. Similarly, the marriage between X’s parents was a “but for” cause, since otherwise X wouldn’t have been around at all to do the shooting.
2. “Substantial factor” test: But as expansive as the “but for” test is, it leaves out one category of acts which almost all courts would hold to be “causes in fact,” even though they are not “but for” causes. Such a cause occurs where an act other than that of the defendant would have been sufficient to bring about the result, but the defendant’s act is a “substantial factor” in bringing about the result nonetheless. Sometimes the defendant’s act in this situation would have been sufficient by itself to bring about the result, but this is not necessary for it to be held to be a “substantial factor,” and therefore a cause in fact.