Causation: How to Ask the Right Questions

In every tort action, the trier of fact must decide whether the act or omission of one or more defendants can be linked to the harm suffered by the plaintiff. This is factual causation. Where there are multiple events that had to occur to bring about the harm, the causal questions become more difficult to frame. Indeed, where multiple events cause harm, an improperly framed causal question may fail to find causation where causation is known to exist.¹

The challenges to framing causal questions in multi-cause cases have given rise to serious confusion and controversy for lawyers and judges. The test for causation is the “but-for” test. It has been suggested, however, that the but-for test is “unworkable” in some situations.² Where the but-for test is considered unworkable, an “alternative” or a “substitute” test has been posited as a solution. This alternative test, referred to as the “material contribution” test³ and later the “material contribution to risk” test,⁴ is, I suggest, of no practical value to litigants and courts as formulated by the Supreme Court of Canada.⁵ The justification for my assertion is beyond the scope of this paper.⁶ I will simply point out that a “material contribution” test is not a test of causation at all. It merely operates to forgive the plaintiff from proving causation. A “material contribution to risk” test, as articulated by the Supreme Court of Canada, is not truly a substitute to but-for because it still imposes a burden on the plaintiff to prove but-for against a group of named defendants.⁷

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