Causation - Material Causation. West v. Knowles
In West v. Knowles (Ont CA, 2021) the Court of Appeal made these comments on the law of causation and it's terminology:
 The respondent agrees that the “but for” test applies in the case at hand, a concession that is well-taken. As this court recognized in Donleavy v. Ultramar Ltd., 2019 ONCA 687, 60 C.C.L.T. (4th) 99, at para. 69, “the critical threshold … for the application of the material contribution to risk approach is the impossibility of proving which of two or more possible tortious causes is in fact a cause of the injury.” It is the “‘but for’ test [that] is generally applied in establishing causation in the tort of negligence”: Donleavy, at para. 62. This would include cases such as the one before me, which involve the alleged acts of a single tortfeasor.
 In resisting this ground of appeal, the respondent submits that the term “material contribution” can be used as an alternative way of describing the “but for” test. He relies, in part, on the pre-Clements decision in Athey v. Leonati, 1996 CanLII 183 (SCC),  3 S.C.R. 458, at para. 41, where Major J. said, “[t]he plaintiff must prove causation by meeting the ‘but for’ or material contribution test.” The respondent therefore submits that we should treat the references to “material contribution” in this jury charge as communicating the “but for” test.
 Given my view that at the end of the charge the jury would have properly understood the law it was to apply, I need not consider whether it remains appropriate after Clements to use “material contribution” language in describing or applying the causation test. However, I do share the view expressed by van Rensburg J.A. in Donleavy, at para. 72, that using “material contribution” language where the “but for” test applies “is a potential source of confusion”. Given that the phrase “material contribution” is used in the law of torts to describe a test that differs from the “but for” test, it may be prudent to avoid using the terms “material contribution” or “contribution” when describing the “but for” causation test.