Tory A. Weigand


The observation by Professor Dobbs that “[t]he substantial factor test is not so much a test as an incantation” remains compelling. The continued and widespread use of “substantial factor” in lieu of “but for” as the predominate means of defining causation in any multiple defendant or multiple cause case is troubling. “Substantial factor” was never intended to supplant “but for” in such cases. This overuse and misunderstanding, which is otherwise accentuated by the Third Restatement’s causal set notion, poses the significant risk that causation can be found when the defendant’s conduct is neither a “but for” nor sufficient cause of the harm or injury. The result is an unacceptable dilution of the requisite nexus for legal responsibility. This Article inspects the origin and sources of substantial factor causation in Massachusetts jurisprudence as well as the approach advocated for by the Third Restatement, both informing and demonstrating the need for greater understanding and restraint as to the otherwise wholesale substitution of “substantial factor” for “but for” in multiple cause or multiple defendant cases.