The Insubstantiality of the 'Substantial Factor' Test for Causation

34 Pages Posted: 17 Feb 2009

See all articles by Joseph Sanders

Joseph Sanders

University of Houston Law Center

Michael D. Green

Wake Forest University - School of Law

William C. Powers, Jr.

University of Texas at Austin

Date Written: May 2008


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.

Keywords: torts, products liabilty, factual causation, substantial-factor test

Suggested Citation

Sanders, Joseph and Green, Michael D. and Powers, Jr., William C., The Insubstantiality of the 'Substantial Factor' Test for Causation (May 2008). Missouri Law Review, Vol. 73, p. 399, 2008, Available at SSRN: or

Joseph Sanders

University of Houston Law Center ( email )

4604 Calhoun Road
Houston, TX 77204-6060
United States
713-743-2125 (Phone)
713-743-2299 (Fax)

Michael D. Green (Contact Author)

Wake Forest University - School of Law ( email )

P.O. Box 7206
Winston-Salem, NC 27109
United States

William C. Powers, Jr.

University of Texas at Austin ( email )

2317 Speedway
Austin, TX 78712
United States

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