Clements v. Clements, 2012 SCC 32
The plaintiff, Clements, drove over a nail while driving his motorcycle with his wife. The nail damaged the tire, which resulted in Clements losing control of the motorcycle. Clements’s wife suffered a brain injury in the crash and sued her husband, alleging that her injury was caused by his negligence in driving an overloaded motorcycle too fast. At trial, Clements was found to be negligent, based on the “material contribution” test. The Court of Appeal set aside the judgment, dismissing the action on the basis that the “material contribution” test was not appropriate in the circumstances and “but for” causation had not been proved.
The key issue for the Supreme Court of Canada was whether the “but for” test or the “material contribution” test applied. Chief Justice McLachlin confirmed that generally the “but for” test is applied to determine causation in a negligence action. The “material contribution” test is only applicable when it is impossible to prove causation on the “but for” test, but is clear that the defendant acted negligently, exposing the plaintiff to an unreasonable risk of injury. This typically occurs when there are multiple tortfeasors at fault and one or more has in fact caused the plaintiff’s injury, but all the defendants are pointing the finger at each other.
Chief Justice McLachlin summarized the present state of the law in Canada with respect to causation at paragraph 46,
• As a general rule, a plaintiff cannot succeed unless she shows as a matter of fact that she would not have suffered the loss “but for” the negligent act or acts of the defendant. A trial judge is to take a robust and pragmatic approach to determining if a plaintiff has established that the defendant’s negligence caused her loss. Scientific proof of causation is not required.
• Exceptionally, a plaintiff may succeed by showing that the defendant’s conduct materially contributed to risk of the plaintiff’s injury, where (a) the plaintiff has established that her loss would not have occurred “but for” the negligence of two or more tortfeasors, each possibly in fact responsible for the loss; and (b) the plaintiff, through no fault of her own, is unable to show that any one of the possible tortfeasors in fact was the necessary or “but for” cause of her injury, because each can point to one another as the possible “but for” cause of the injury, defeating a finding of causation on a balance of probabilities against anyone.
The Supreme Court found that the trial judge made two errors: (1) insisting on scientific precision in the evidence as a condition of finding “but for” causation, and (2) applying a material contribution test in “a simple single-defendant case”. The matter was returned to the trial judge to be dealt with on the basis of “but for” causation.