The law does not require the plaintiff to prove causation with scientific certainty. She is only required to prove that it is more probable than not, that her injury triggered the initial onset of her MS symptoms. She can accomplish this, by showing either that her MS symptoms would not have occurred "but for" her physical injury, or that her physical injury "materially contributed" to the initial occurrence of her MS symptoms. She does not have to prove that her injury was the sole cause of the onset of her MS symptoms, but only that the injury was a "material" contributing factor, in the sense that it was a contributing factor beyond the "de minimis" range. These principles are stated in Athey v. Leonati (1996), 1996 CanLII 183 (SCC), 140 D.L.R. (4th) 235 (S.C.C.).
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