What is the test for determining whether there is a causal link between negligence and injury?

The test for causation is the “but for” test. In determining whether there is a causal link between the defendant’s negligence and the plaintiff’s injuries, the court must consider whether, but for the defendant’s acts, the plaintiff’s damages would have been incurred. The governing principle is that the defendant need not put the plaintiff in a better position than their original position and should not compensate the plaintiff for any damages they would have suffered anyway: Blackwater v. Plint, 2005 SCC 58 at para. 78.

The plaintiff must establish on a balance of probabilities that the defendant’s negligence caused or materially contributed to an injury. The defendant’s negligence need not be the sole cause of the injury. As long as a defendant is part of the cause of an injury, the defendant is liable, even though his act alone was not enough to create the injury: Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458 at paras. 13-17.