In Clements v. Clements, 2012 SCC 32 (“Clements”), the Supreme Court of Canada clarified the circumstances in which a plaintiff in a negligence action may establish causation on the basis that the defendant’s conduct materially contributed to the risk that gave rise to the plaintiff’s injury, rather than the “but for” test.

The Court held that the “material contribution to risk” test will apply only where the plaintiff’s injury would not have occurred “but for” the negligence of two or more wrongdoers, each of which are potentially responsible for the loss, and the plaintiff, through no fault of their own, is unable to show that any one of the possible wrongdoers was the “but for” cause of the injury.

Background

The parties went on a motorbike trip. The defendant was driving the bike and the plaintiff was riding behind on the passenger seat. The weather was wet and the bike was overloaded with weight. Unbeknownst to the parties, a nail had punctured the bike’s rear tire. Although the defendant was travelling in a 100 km/h zone, he accelerated to at least 120km/h in order to pass a car. As he did so, the nail fell out of the tire, the rear tire deflated, and the bike began to wobble. The defendant was unable to bring the bike under control, and it crashed. The plaintiff was thrown off and suffered a severe traumatic brain injury. She sued the defendant, claiming that her injury was caused by his negligent operation of the bike.

In order to succeed in a negligence claim, a plaintiff must establish that:

• the defendant owed the plaintiff a duty of care;

• the defendant breached their duty of care;

• the plaintiff suffered damages; and

• the defendant’s breach of their duty of care caused the plaintiff’s damages.

In Clements, there was little dispute with respect to the first three elements. The key issue was whether the defendant’s negligence caused the plaintiff’s injury.

In general, the test for showing causation is the “but for” test. This means that a plaintiff cannot establish causation unless the plaintiff shows that they would not have suffered the loss “but for” the defendant’s breach of their duty of care.  In other words, the defendant’s breach must have been necessary in order for the the plaintiff’s loss to have occurred.

At trial, the defendant called an expert witness who testified that the probable cause of the accident was the tire puncture and the deflation, and that the accident would have occurred even without the plaintiff’s negligence. The trial judge rejected this evidence, but did not conclude that the plaintiff’s injury would have occurred “but for” the defendant’s breach. Instead, the trial judge held that the defendant’s breach materially contributed to the plaintiff’s injury, and that this was sufficient to establish causation.

Decision

The key issue before the Supreme Court of Canada was whether the “but for” test for causation applied, or whether causation could be established on the basis of the “material contribution to risk” test.

Chief Justice McLachlin, writing for the majority, clarified that although a plaintiff must generally establish causation on the basis of the “but for” test, a plaintiff may, in exceptional circumstances, establish causation by showing that the defendant’s breach materially contributed to the risk of the plaintiff’s injury. In order to do so, the plaintiff must establish that:

• the damage would not have occurred “but for” the negligence of two or more wrongdoers, each of which are possibly responsible for the loss; and

• the plaintiff, through no fault of their own, is unable to show that any one of the possible wrongdoers in fact was the necessary or “but for” cause of her injury, because each can point to one another as a possible “but for” cause of the injury, defeating a finding of causation on a balance of probabilities against anyone.

In these exceptional circumstances, the “material contribution to risk” test will, in the Court’s view, result in a fair outcome. The plaintiff will have established “but for” causation with respect to the group of defendants as a whole, each defendant will have failed to act with the necessary care to avoid potentially causing the plaintiff’s loss, and each defendant may have in fact caused the plaintiff’s loss.

In the result, the Court concluded that the “material contribution to risk” test did not apply. Because the case involved a single defendant, the only issue was whether the injury would have occurred “but for” the defendant’s breach. Accordingly, the Court returned the matter to the trial judge to be assessed on the basis of the “but for” test.