Causation

The two-step analysis. The conventional wisdom about the causation requirement in both criminal law and torts is that it in reality consists of two very different requirements. The first requirement is that of "cause-in-fact." This is said to be the true causal requirement because this doctrine adopts the scientific notion of causation. Whether cigarette smoking causes cancer, whether the presence of hydrogen or helium caused an explosion, are factual questions to be resolved by the best science the courts can muster. By contrast, the second requirement, that of "proximate" or "legal" cause, is said to be an evaluative issue, to be resolved by arguments of policy and not arguments of scientific fact. Suppose a defendant knifes his victim, who then dies because her religious convictions are such that she refuses medical treatment. Has such a defendant (legally) caused her death? The answer to such questions, it is said, depends on the policies behind liability, not on any factual issues.

The counterfactual analysis of cause-in-fact. By far the dominant test for cause-in-fact is the common law and Model Penal Code "sine qua non," or "but-for" test (MPC §2.03(1)). Such a test asks a counterfactual question: "but for the defendant's action, would the victim have been harmed in the way the criminal law prohibits?" This test is also sometimes called the necessary condition test, because it requires that the defendant's action be necessary to the victim's harm. The appeal of this test stems from this fact. The test seems to isolate something we seem to care a lot about, both in explaining events and in assessing responsibility for them, namely, did the defendant's act make a difference? Insofar as we increase moral blameworthiness and legal punishment for actors who do cause bad results (not just try to), we seemingly should care whether a particular bad result would have happened anyway, even without the defendant.

The policy analysis of legal cause. There is no equivalently dominant test of legal or proximate cause. There are nonetheless four distinguishable sorts of tests having some authority within the legal literature. The first of these are what we may call "ad hoc policy tests" (Edgarton). The idea is that courts balance a range of policies in each case that they adjudicate where a defendant has been found to have caused-in-fact a legally prohibited harm. They may balance certain "social interests" like the need for deterrence with certain "individual interests" like the unfairness of surprising a defendant with liability. Courts then decide wherever such balance leads. Whatever decision is reached on such case-by-case policy balancing is then cast in terms of "proximate" or "legal" cause. Such labels are simply the conclusions of policy balances; the labels have nothing to do with causation in any ordinary or scientific sense.

The second sort of test here is one that adopts general rules of legal causation. Such rules are adopted for various policy reasons also having nothing to do with causation, but this "rules-based" test differs from the last by its eschewal of case-by-case balancing; rather, per se rules of legal causation are adopted for policy reasons. Thus, the common law rule for homicide was that death must occur within a year and a day of the defendant's harmful action, else the defendant could not be said to have legally caused the death. Analogously, the "last wrongdoer rule" held that when a single victim is mortally wounded by two or more assailants, acting not in concert and acting seriatim over time, only the last wrongdoer could be said to be the legal cause of the death (Smith, p. 111). Such sorts of tests also found a temporary home in tort law with its "first house rule," according to which a railroad whose negligently emitted sparks burned an entire town was only liable for the house or houses directly ignited by its sparks, not for other houses ignited by the burning of those first burnt houses (Ryan v. New York Central R.R., 35 N.Y. 210, 91 Am. Dec.49 (1866)). There is no pretense in such rules of making truly causal discriminations; rather, such rules were adopted for explicit reasons of legal policy.

The third sort of test here is the well-known foreseeability test (Moore, 1997, pp. 363–399). Unlike the "rules-based" test, here there is no multiplicity of rules for specific situations (like homicide, intervening wrongdoers, railroad fires, etc.). Rather, there is one rule universally applicable to all criminal cases: was the harm that the defendant's act in fact caused foreseeable to him at the time he acted? This purportedly universal test for legal causation is usually justified by one of two policies: either the unfairness of punishing someone for harms that they could not foresee, or the inability to gain any deterrence by punishing such actors (since the criminal law's threat value is nonexistent for unforeseeable violations).

Some jurisdictions restrict the foreseeability test to one kind of situation. When some human action or natural event intervenes between the defendant's action and the harm, the restricted test asks whether that intervening action or event was foreseeable to the defendant when he acted (Moore, 1997, p. 363 n.1). This restricted foreseeability test is like the restricted rules we saw before and is unlike the universal test of legal causation the foreseeability test usually purports to be.

The fourth and last sort of test here is the "harm-within-the-risk" test (Green). Like the foreseeability test, this test purports to be a test of legal cause universally applicable to all criminal cases. This test too is justified on policy grounds and does not pretend to have anything to do with factual or scientific causation. Doctrinally, however, the test differs from a simple foreseeability test.

Consider first the arena from which the test takes its name, crimes of risk creation. If the defendant is charged with negligent homicide, for example, this test requires that the death of the victim be within the risk that made the actor's action negligent. Similarly, if the charge is manslaughter (for which consciousness of the risk is required in some jurisdictions), this test requires that the death of the victim be within the risk the awareness of which made the defendant's action reckless.

Extension of this test to nonrisk-creation crimes requires some modification. For crimes of strict liability, where no mens rea is required, the test requires that the harm that happened be one of the types of harms the risk of which motivated the legislature to criminalize the behavior. For crimes requiring knowledge or general intention for their mens rea, the test asks whether the harm that happened was an instance of the type of harm foreseen by the defendant as he acted. For crimes requiring purpose or specific intent for their mens rea, the test asks whether the harm that happened was an instance of the type of harm the defendant intended to achieve by his action.

What motivates all of these variations of the harm-within-the-risk test is the following insight: when assessing culpable mens rea, there is always a "fit problem" (Moore, 1997, pp. 469–476). Suppose a defendant intends to hit his victim in the face with a stick; suppose further he intends the hit to put out the victim's left eye. As it happens, the victim turns suddenly as he is being hit, and loses his right ear. Whether the harm that happened is an instance of the type of harm intended is what the present author calls the "fit problem." Fact finders have to fit the mental state the defendant had to the actual result he achieved and ask whether it is close enough for him to be punished for a crime of intent like mayhem. (If it is not close enough, then he may yet be convicted of some lesser crime of battery or reckless endangerment.)

The essential claim behind the harm within the risk test is that "legal cause" is the inapt label we have put on a problem of culpability, the fit problem. Proponents of this test urge that legal cause, properly understood, is really a mens rea doctrine, not a doctrine of causation at all.