What is the test for establishing causation in tort law?

Athey v. Leonati, supra, is the leading Canadian case on causation in tort law. In Athey, Major J. reiterated the following well-established principles: (1) The general, but not conclusive, test for proof of causation is the "but for" test, which requires a plaintiff to show that his or her injury would not have occurred but for the negligence of the defendant (para. 14). (2) In certain circumstances, where the "but for" test is un-workable, causation may also be established where it is demonstrated that the defendant's negligence "materially contributed" to the occurrence of the tort victim's injury. It is not necessary for the plaintiff to establish that the defendant's negligence was the sole cause of the injury (paras. 15 and 17). (3) Liability will be imposed on a defendant for injuries caused or materially contributed to by his or her negligence. That liability is not reduced by the existence of other non-tortious contributing causes (paras. 22 and 23). (Citations omitted)