What is the test for a plaintiff to recover damages from a defendant for negligence?

For a plaintiff to recover damages in tort, the plaintiff must show on a balance of probabilities that “but for” the defendant’s negligent act, the injury would not have occurred. Inherent in the phrase “but for” is the requirement that the defendant’s negligence was necessary to bring about the injury – in other words that the injury would not have occurred without the defendant’s negligence. See Clements v. Clements, 2012 SCC 32, at paras. 8 and 13. Causation need not be proved with scientific precision. It is not necessary for the plaintiff to establish that the defendant's negligence was the sole cause of the injury. As long as a defendant is part of the cause of the injury, the defendant is liable, even though his act alone was not enough to create the injury. There is no basis for a reduction of liability because of the existence of other preconditions: defendants remain liable for all injuries caused or contributed to by their negligence. See Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458, at paras. 13-17. The plaintiff is to be placed in the same position he or she would have been if not for the defendant’s negligence.