Causation in personal injury cases clarified
In Clements v. Clements  S.C.J. No. 32 the Supreme Court of Canada examined causation where several possible causes, but only one tortfeaser, may have caused injury. The case presented an unusual set of facts and unusual circumstances. Most frequently, issues of causation arise when the court examines which of two or more tortfeasors caused injury.
Facts: The Plaintiff, Ms. Clements, a passenger on a motorcycle driven by her husband, was severely injured when the motorcycle became unstable and overturned while passing a car on the highway. She argued the accident was caused by a combination of overloading and excessive speed on a wet road. In the alternative, she submitted that if she could not satisfy a but for test, then there were “special circumstances” that warranted causation being decided in her favour on the basis of a material contribution test.
A tire on the motorbike had been punctured by a nail and deflated when the Defendant sped up to pass the car. Mr. Clements’ position was that because of the deflated tire, he would have been unable to bring the motorcycle to a safe stop even if he had been travelling slower with a lighter load. Expert reconstruction evidence for the Plaintiff did not prove scientifically that the Defendant’s negligence, rather than the deflated tire, caused her injuries.
Trial decision: The critical issue for the trial judge was causation; whether Mr. Clements’s negligent acts caused the injuries sustained by Mrs. Clements. The judge allowed a material contribution test observing that there was a common sense relationship between excessive speed/weight and the ability to recover safely from a weave instability. The defendant was found 100% liable.
Court of Appeal decision: The British Columbia Court of Appeal per Frankel, J.A. observed that once the trial judge determined Mrs. Clements had failed to establish that the motorcycle would not have capsized but for Mr. Clements’s negligence, he should have found that causation had not been proven. Given the current state of knowledge, it was not possible to prove whether the negligent actions of the defendant caused harm. The court held it must not fix Mr. Clements with liability when Mrs. Clements was unable to show factually that his negligence was a cause of her damages. The appeal was allowed, and the action was dismissed against Mr. Clements.
Supreme Court of Canada: The Supreme Court of Canada examined the issue of whether the usual but for test for causation in a negligence action applied, as the Court of Appeal held, or whether a material contribution approach sufficed, as the trial judge held.
The court reviewed the current state of the law of causation.
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 trial judge accepted evidence to the effect that overloading would have increased instability in the event of a weave caused by tire deflation. He also noted expert evidence to the effect that instability due to tire deflation increases with speed and that it was impossible to predict without tests whether the capsize would have occurred at a lower speed. However, the trial judge rejected the evidence of the expert that the accident would have happened even if the defendant had not negligently overloaded his bike and driven too fast.
Having rejected the defendant’s expert evidence that the accident would have happened regardless of the excess speed and excess weight, the judge was left with the fact that while there was no scientific proof one way or the other, “ordinary common sense” supported the causal relationship between the injury and the excessive speed and weight.
The court found the trial judge made two errors.
The first error was to insist on scientific reconstruction evidence as a necessary condition of finding but for causation.
The trial judge’s second error was to apply a material contribution to risk test. The special conditions that permit resort to a material contribution approach were not present. Clements was not a case where the loss would not have occurred but for the negligence of two or more possible tortfeasors, but the plaintiff could not establish on a balance of probabilities which negligent actor or actors caused the injury. This was a single-defendant case: the only issue was whether but for the defendant’s negligent conduct, the injury would have been sustained.
The court held that a material contribution test was not applicable. The matter was returned to the trial judge to be dealt with on the correct basis of but for causation.
One interesting aspect of the case was the dissenting judges’ argument. While the majority found the case should be returned for retrial, two judges argued that, as found by the B.C. Court of Appeal, that the case should be dismissed, given the trial judge’s finding that Ms. Clements failed to establish that the defendant’s negligence caused her injuries.