Wright: Causation in tort law

Wright. 1985. Causation in tort law. California Law Review 73:1735.

In Brief

The traditional legal model of "but-for" causation (necessary condition causation), while fundamental to the idea of causation in general, is insufficient to account for causation in overdetermined causation cases. Therefore, the NESS test [necessary element of a sufficient set] is needed in these overdetermined cases, which comprise preemptive causation and duplicative causation situations. The key idea here is that one's action can be a contributing causal condition, even if the "but for" test is not met.

Important Definitions

• "but for" causation (necessary condition): an act or omission was a cause of an injury if and only if, but for the act, the injury would not have occurred. That is, the act must be a necessary condition for the occurrence of the injury. The test reflects a deeply rooted belief that a condition cannot be a cause of some event unless it is, in some sense, necessary for the occurrence of the event. (1775). Comment: This is analogous to the concept of "decisiveness" in voting studies: Your vote makes your candidate get 50% + 1 of the vote, pivotally determining the vote outcome. But for my vote, my candidate would not have won.
• overdetermined causation cases: cases in which two or more factors each would have been sufficient to produce the injury, so that none of them was a necessary condition for the injury. In other words, cases in which a factor other than the specified act would have been sufficient to produce the injury in the absence of the specified act, but its effects either: (1) were preempted by the more immediately operative effects of the specified act; or (2) combined with or duplicated those of the specified act to jointly produce the injury. (1775).
  • An example of an overdetermined case: Two separate arsonists start two separate fires. The fires merge, then destroy a house. Either fire alone would have destroyed the house, but neither arsonist is guilty under the "but for" test; without the first arsonist, the house still would have been destroyed, but without the second arsonists, the house would still have been destroyed, therefore neither arsonist "caused" the destruction. Thus, we need a better theory than the "but for" test.
• NESS test: a particular condition was a cause of (a condition contributing to) a specific consequence if and only if it was a necessary element of a set of antecedent actual conditions that was sufficient for the occurrence of the consequence. Wright says that the NESS test incorporates the indispensable notion of necessity, but subordinates it to the notion of sufficiency.
  • Example of NESS: Suppose there are five voters, A, B, C, D, and E. Suppose A, B, C, and D favor an initiative, and E does not. It only takes three of five votes to win, but four of five vote. According to the "but for" test, none of these voters was decisive; four votes overdetermines the outcome. But let's apply the NESS test to show that A, B, C, and D contributed to the outcome. There are four possible sets which are (minimally) sufficient to ensure the outcome, and which actually occured: ABC, ACD, BCD, ABD. Note that each of A, B, C, and D is a necessary member of at least one of these sets--and each set is individually sufficient to ensure the outcome. By the NESS test, then, each of A, B, C, and D is responsible (by contributory causation) for the outcome.
  • Other authors take this a step further to rank each actor's responsibility for the outcome. Note that A belongs to three of the four possible minimally sufficient sets; so call A's responsibility 3/4. In this particular case, all four participants (A, B, C, and D) would have 3/4 responsibility. But it doesn't need to be equal. In other situations, we'll see that some individuals have a higher rank in this "power index" than others. (Note that by this method, each individual's responsibility would be 1 if the "but for" test held.)

Comments and Criticism

It seems to me that efforts to modify the "but for" test to handle the overdetermined causation problem are motivated by our concern for the moral culpability of actors whom the technical application of the "but for" test would absolve. This relates to the Goldman (2002) piece because we seem to instinctively think that even if this person was not the "but for" cause, he is still somehow morally responsible for what happened. As Wright puts it, the courts feel compelled to depart from the "but for" test in overdetermined causation cases because, although the but-for test is not satisfied, "it is clear that the defendant's tortious conduct contributed to the injury." (1792) (emphasis added). In other words, we know that the defendant "had something to do with" the plaintiff's injury.

The pollution example is probably the best analogy to voting. However, one should note that this is an expansion of the overdetermined causation idea (because each factor alone is not sufficient in and of itself to cause the injury) and that this expansion is a direct result of the application of the NESS test.

In the pollution example, we are told to assume that 5 units of pollution were necessary and sufficient for the injury and that each of 7 defendants discharged one unit of pollution. Wright points out that while each defendant can truthfully say that its one unit was neither necessary nor independently sufficient for the injury, each defendant's one unit was necessary for the sufficiency of a set of actual antecedent conditions that included only four of the other units, and the sufficiency of this particular set of actual antecedent conditions was not affected by the existence of two additional duplicative units. If we apply this rationale to voting, we see the following: Candidate A needs 51 votes out of 100 to win, yet 70 people vote for candidate A. While each voter can say that her one vote was neither necessary nor independently sufficient for the victory of candidate A, each nonetheless knows that her vote contributed to causing the victory.

Question to Consider

What does Wright's preemptive causation story tell us, if anything, about the problem of the West Coast voter in Presidential elections? Goldman states in his article that national elections featuring different time zones and/or different poll-closing times are "flawed executions of the traditional conceptualization of elections." (278). However, what is the causation story here? Are West Coast voters' votes causally preempted if it is clear that one candidate already has won enough votes in the electoral college? Is it correct to say, in that case, that West Coast voters cannot contribute causally to the outcome because the outcome already has been determined?