The SCC restored the trial judgement, while emphasizing that the basic test for determining causation remains the “but for” test. The Plaintiff bears the burden of proving that but for the defendant’s negligence, the injury would not have occurred, after which contributory negligence may be apportioned.18 The SCC stated that the “but for” test ensures that compensation is only made where a substantial connection between the injury and the defendant’s conduct is present, and the defendant will not be held liable for injuries where they may very well be due to factors unconnected to the defendant and not the fault of anyone.19
The “material contribution to risk” test is only applied in special circumstances where firstly, it is impossible for the plaintiff to prove that the defendant’s negligence caused the plaintiff’s injury using the “but for” test.20 This impossibility must be due to factors outside the plaintiff’s control, such as the current limits of scientific knowledge. Secondly, the plaintiff must show a breach of a duty of care that exposes the plaintiff to an unreasonable risk of injury.
Clements v. Clements (2012)
The SCC decision in Clements v. Clements21 (“Clements”), while not explicitly stating so, effectively overruled the line of authority that arose from the BCCA decision in Moore and that was reiterated in the later overturned BCCA decision in Ediger v. Johnston.22
In this case, the defendant was operating the motorcycle with the plaintiff, his wife, riding behind him as a passenger. The motorcycle was overloaded and a nail had punctured the rear tire. As the defendant accelerated, the nail fell out and caused the rear tire to deflate. The motorcycle crashed and the plaintiff suffered a brain injury. She sued the defendant, claiming her injury was caused by his negligent operation of the motorcycle and she was successful at trial.
The trial judge found the defendant’s negligence had contributed to the plaintiff’s injury, using a “material contribution to risk” test. The trial judge stated that the plaintiff, “through no fault of her own is unable to prove that but for the defendant’s negligence, she would not have been injured, due to the limitations of the scientific reconstruction evidence.”23 The BCCA set aside the trial judgment, finding that the “but for” test had not been satisfied and the “material contribution to risk” test did not apply because the exceptional circumstances allowing its use were not present.
The case was then appealed to the SCC, which found that the trial judge erred in using the “material contribution to risk” test. A new trial was ordered. The SCC stated that the test for showing causation is the “but for” test and the requirement is that the defendant’s negligence was necessary to bring about the injury, which is a factual inquiry.24 As emphasized in Snell, the test is to be applied in a robust common sense fashion, and there is no need for scientific evidence of the precise contribution the negligence made to the injury.25 A common sense inference of but for causation from proof of negligence usually flows without difficulty. Evidence connecting the negligence to the injury may permit the judge, depending on the circumstances to infer causation.26
The SCC further defined the strict circumstances under which a “material contribution to risk” test may be utilized, as stated in Resurfice. The “material contribution to risk” test achieves fairness by allowing compensation for a plaintiff who has already established but for causation globally for multiple defendants, each contributing to the risk of harm, but finds it impossible to determine which specific defendant in fact caused the injury. The requirement of “impossible to prove” does not mean scientific impossibility, but rather the impossibility to determine on a balance of probabilities which specific tortfeasor in fact caused the injury.27
