The Insubstantiality of the 'Substantial Factor' Test for Causation

Abstract

The Second Restatement of Torts continued the use of the "substantial factor" test for causation. This article reconsiders that test in a causally problematic context, asbestos litigation. It considers how courts have used and abused the substantial factor test and concludes that its use is unfortunate because of its fuzziness and lack of analytical rigor. There are obvious advantages to returning to the but-for test of causation, as has the Third Restatement of Torts. The ambiguity surrounding the substantial factor test leads to inconsistent results, at least across jurisdictions. More importantly, the test gives no clear guidance to the factfinder about how one should approach the causal problem. It also permits courts to engage in fuzzy-headed thinking about what sort of causal requirement ought to be imposed on plaintiffs, especially in cases that present complications in the availability of evidence of such. The but-for test, on the other hand, offers a roadmap on how to think about causation.But this article can't demonstrate the advantage of but-for causation over the substantial factor approach in a context like asbestos, where proof of causation is not possible. Under the circumstances this article does not take issue with jurisdictions that relax their proof requirements and permit plaintiffs to do something less than show that exposure to a given defendant's asbestos products was a factual cause of the harm. But-for causation simply won't work in these circumstances. Nor does this article criticize the effort on the part of courts to limit the extent of liability for defendants who have made small contributions to the overall dose to which the plaintiff was exposed. But even in this situation, the substantial factor test obfuscates what is really going on and permits courts to proceed without grappling with the real issues presented and resolving them on a transparent and honest basis. Recognition of the very difficult problems of proof in asbestos, a predicate to a coherent response to that problem, can't proceed without a clear grasp on what we mean by causation and the role of but-for in that definition.