Causation

The problems with the conventional analysis of causation have tempted many to abandon the conventional analysis, root and branch. This generates a search for a unitary notion of causation that is much more discriminating (in what it allows as a cause) than the hopelessly promiscuous counterfactual cause-in-fact test of the conventional analysis. Indeed, the search is for a unitary concept of causation that is so discriminating that it can do the work that on the conventional analysis is done by both cause-in-fact and legal cause doctrines. It is far from obvious that causation is in fact a sufficiently discriminating relation that it can do this much work in assigning responsibility. Nonetheless, there are four such proposals in the academic literature, each having some doctrinal support in the criminal law.

Space time proximateness and the substantial factor test. The oldest of the proposals conceives of causation as a metaphysical primitive. Causation is not reducible to any other sort of thing or things, and thus there is little by way of an analysis that one can say about it. However, the one thing we can say is that the causal relation is a scalar relation, which is to say, a matter of degree. One thing can be more of a cause of a certain event than another thing. Moreover, the causal relation diminishes over the number of events through which it is transmitted. The causal relation is thus not a fully transitive relation, in that if event c causes e, and e causes f, and f causes g, it may still be the case that c does not cause g.

On this view of causation, all the law need do is draw the line for liability somewhere on the scale of causal contribution. On matters that vary on a smooth continuum, it is notoriously arbitrary to pick a precise break-point; where is the line between middle age and old age, red and pink, bald and not-bald, or caused and not caused? This approach thus picks an appropriately vague line below which one's causal contribution to a given harm will be ignored for purposes of assessing responsibility. Let the defendant be responsible and liable for some harm only when the degree of his causal contribution to that harm has reached some non-de minimus, or "substantial," magnitude. This is the "substantial factor" test, first explicitly articulated by Jeremiah Smith (1911) and then adopted (but only as a test of cause in fact, not of causation generally) by the American Law Institute in its Restatement of Torts. To the common objection that the test tells us little, its defenders reply that that is a virtue, not a vice, for there is little to be said about causation. It, like obscenity, is something we can "know when we see it," without need of general definitions and tests.

Force, energy, and the mechanistic conception of cause. Other theorists have thought that we can say more about the nature of the causal relation than that it is scalar and diminishes over intervening events. On this view the nature of causation is to be found in the mechanistic concepts of physics: matter in motion, energy, force (Beale; Epstein; Moore, 1999). This test is similar to the substantial factor view in its conceiving the causal relation to be scalar and of limited transitivity.

This view handles easily the overdetermination cases that are such a problem for the conventional analysis. When two fires join, two bullets strike simultaneously, two motorcycles scare the same horse, each is a cause of the harm because each is doing its physical work. When one non-mortal wound is inflicted together with a larger, mortal wound, the victim dying of loss of blood, each is a cause of death because each did some of the physical work (loss of blood) leading to death.

Such a mechanistic conception of causation is mostly a suggestion in the academic literature because of the elusive and seemingly mysterious use of "energy" and "force" by legal theorists. One suspects some such view is often applied by jurors, but unless theorists can spell out the general nature of the relation being intuitively applied by jurors (as is attempted in Fair), this test tends to collapse to the metaphysically sparer substantial factor test.

Aspect causation and the revised counterfactural test. There is an ambiguity about causation that we have hitherto ignored but which does find intuitive expression in the decided cases. The ambiguity lies in the sorts of things that can be causes and effects, what are called the "relata" of the causal relation. The usual assumption is that causal relata are whole events; in the phrase "the firing of his gun caused the death of the victim," the descriptions "the firing of his gun" and "the death of the victim" each name events. Sometimes, however, we might say, "it was the fact that the gun fired was of such large caliber that caused the victim to die." That it was a large-caliber-gun firing is an aspect of the event. The whole event was the firing of the gun; one of that event's properties was that it was a large-caliber-gun firing.

Lawyers adopt this shift in causal relata when they distinguish the defendant's action as a cause, from some wrongful aspect of the defendant's action which is not causally relevant. Thus, when an unlicensed driver injuries a pedestrian, they say: "while the driving did cause the injuries, the fact that it was unlicensed driving did not."

A restrictive notion of causation can be found by restricting things eligible to be causal relata to aspects of a defendant's action that make him culpable (either by foresight, intent, or risk). Typically, this restriction is married to some counterfactual conception of causation (Wright, 1985). The resulting conception of causation promises fully as discriminating a notion as was achieved by the harm-within-the-risk approach of the conventional analysis (for notice that this conception really is just harm-within-the-risk conceptualized as a true causal doctrine rather than a construction of legal policy). Such a conception of causation must thus face the challenges faced by the harm-within-the-risk conception, namely, the inadequacy of either analysis to deal with intervening causation, remoteness, freakishness of causal route, and so on. In addition, this proposed conception faces metaphysical hurdles not faced by the harm-within-the-risk analysis, for it must make sense of the idea of aspects of events being causes, rather than events themselves.

Hart and Honore's direct cause test. Beginning in a series of articles in the 1950s and culminating in their massive book, Causation in the Law (1959), Herbert Hart and Tony Honore sought to describe a unitary conception of causation they saw as implicit both in the law and in everyday usages of the concept. One can see their concept most easily in three steps. First, begin with some version of the counterfactual analysis: a cause is a necessary condition for its effect (or perhaps a NESS condition). Second, a cause is not any necessary condition; rather, out of the plethora of conditions necessary for the happening of any event, only two sorts are eligible to be causes. Free, informed, voluntary human actions, and those abnormal conjunctions of natural events we colloquially refer to as "coincidences," are the two kind of necessary conditions we find salient and honor as "causes" (versus mere "background conditions"). Third, such voluntary human action and abnormal natural events cause a given effect only if some other voluntary human action or abnormal natural event does not intervene between the first such event and its putative effect. Such salient events, in other words, are breakers of causal chains as much as they are initiators of causal chains, so that if they do intervene they relegate all earlier such events to the status of mere background conditions.

Hart and Honore built on considerable case law support for their two candidates for intervening causes (Carpenter, pp. 471–530). Indeed, it is arguable that the basic distinction between principal and accomplice liability depends in part on this conceptualization of causation (Kadish). One concern for this view of causation, nonetheless, is the worry that it is incomplete with respect to the remoteness range of issues usually dealt with under the rubric of "legal cause" in the law. Causation fades out gradually as much as it breaks off suddenly in the law, and the Hart and Honore analysis ignores this.