What is the test for causation in tort law?

Causation in tort law is essentially a practical question of fact which can best be answered by ordinary common sense rather than abstract metaphysical theory. Causation in tort does not require scientific or precise proof. Courts apply the “but for” causation test in a robust, common sense manner. If the plaintiff adduces evidence connecting the defendant’s breach of duty to the plaintiff’s injury, the court may infer that the defendant’s tort caused the loss even in the absence of scientific evidence of the defendant’s precise contribution: Snell v. Farrell, 1990 CanLII 70 (SCC), [1990] 2 S.C.R. 311. The legal burden remains with the plaintiff, but in the absence of evidence to the contrary adduced by the defendant, an inference of causation may be drawn although positive or scientific proof of causation has not been adduced: Snell, at para. 34.

When the plaintiff adduces evidence connecting the defendant’s tortious conduct to the injury suffered, it is appropriate for the court to infer the defendant’s liability for these injuries in the absence of a credible explanation by the defendant. Evidence is to be weighed according to the proof which it was in the power of one side to have produced and in the power of the other to have contradicted: Blatch v. Archer (1774), 98 E.R. 969, at p. 970.