Testing Causation

The Supreme Court of Canada’s June 2012 decision in Clements v. Clements reinforces the notion that the “but for” test remains the test for proof of causation in negligence, and that exceptions to its application will be few. It also suggests the “material contribution” test ought to be applied only in cases involving multiple concurrent tortfeasors [i.e. wrongdoers], or in other very limited circumstances.

Background

When seeking to recover damages in connection with harm resulting from another’s negligence, an injured party must establish on a balance of probabilities that the tortfeasor caused the injury in question. The requirement that an injured party establish a causal connection between the negligent act and the resultant harm anchors the law of negligence to one of its underlying purposes — corrective justice.

Canadian courts have long applied the “but for” test to the proof of causation. The test is applied to cases arising from both single-cause and multi-cause injuries and requires a plaintiff to demonstrate that “but for” the defendant’s negligent act, the injury would not have occurred.

However, the Supreme Court has ruled in the past, in certain exceptional circumstances, a court may apply the “material contribution” test in place of the “but for” test. The “material contribution” test allows an injured party to avoid the need to prove “but for” causation and only requires proof that the negligent action materially contributed to the risk of harm.

In Clements, the Supreme Court narrowed the application of the “material contribution” test. At the same time, in obiter1 comments, it suggested the test’s application could be expanded in the future. 

The Clements Case

Joseph and Joan Clements were involved in a motorcycle accident, with Joseph Clements operating the motorcycle, and Joan Clements riding behind him as a passenger. The bike was about 100 pounds overloaded. Unknown to Joseph Clements, a nail had punctured the bike’s rear tire. As he accelerated to pass a car, the nail fell out causing the rear tire to deflate. Unable to bring the bike under control, he crashed the bike. As a result, Joan Clements, the passenger, suffered a traumatic brain injury. She then sued Joseph Clements, claiming her injury was caused by his negligent operation of the bike.

The trial judge found that Joseph Clements’ negligence had contributed to Joan Clements’ injury. In finding liability, he used a “material contribution to risk” test for causation instead of the usual “but for” test. He felt that on an evidentiary basis, Joan Clements could not establish that her injuries would not have occurred “but for” Joseph Clements’ negligence in overloading the motorcycle and driving too quickly. Since it was “through no fault of her own” that Joan Clements was unable meet the “but for” standard of proof, the trial judge felt that exceptional circumstances existed warranting the application of the “material contribution” test. Joan Clements was therefore successful at trial.

The case was appealed to the British Columbia Court of Appeal, where the trial judge’s decision was set aside. The court held that the “but for” test to establish causation had not been satisfied and that the “material contribution to risk” test did not apply because the exceptional circumstances allowing its use were not present. The case was appealed to the Supreme Court.

The Supreme Court’s Decision

The central issue before the Supreme Court was: In what type of exceptional circumstances might a court apply the “material contribution” test in place of the “but for” test of causation? This

issue required some clarification, following previous cases in the highest court — including Resurfice Corp v. Hanke [2007], Athey v. Leonati [1996] and Snell v. Farrell [1990] — that dealt with various circumstances in which the courts might depart from traditional “but for” test for causation.

In Clements, the Supreme Court was unanimous in concluding that a “material contribution to risk” test was not applicable on the facts. The court restated its finding in Resurfice that the use of a “material contribution to risk” test as a replacement for the “but for” test may be appropriate where:

• it is “impossible” for the plaintiff to prove causation on the “but for” test; and

• it is clear the defendant breached its duty of care (acted negligently) in a way that exposed the plaintiff to an unreasonable risk of injury.

Using the foundation provided in Resurfice, the Supreme Court in Clements sought to define what is meant by “impossible to prove.” The court rejected the suggestion that the inability to provide factual proof sufficient for “but for” causation allows a court to apply the “material contribution to risk” test. Further, the Supreme Court clarified that scientific precision is not necessary to establish “but for” causation. Instead, the “but for” test allows judges to make common sense inferences from the facts to determine that the defendant’s negligence probably caused the loss. The Supreme Court highlighted that to allow the “material contribution” test to apply in such circumstance would “fundamentally change the law of negligence” and diminish the underlying connection of causation to corrective justice.

In Clements, the Supreme Court suggests the “impossibility of proof” required to trigger application of the “material contribution” test is the kind of logistical impossibility arising in cases involving multiple defendants, in which each contributed to the risk of harm, but it is impossible to know which of them, in fact, caused the loss. In such circumstances, the “but for” test will break down when applied to any one individual defendant since it is impossible for the plaintiff to show whose actions actually caused the injury.

The Supreme Court went so far as to say that the “material contribution” test generally ought not to be applied to straightforward negligence cases involving a single defendant (although its application to single-defendant cases was not completely ruled out). In making this statement, the Supreme Court appears to have limited the application of the “material contribution” test to cases of multiple, concurrent tortfeasors.

Supreme Court of Canada Chief Justice Beverley McLachlin made an interesting obiter comment at paragraph 44 of the Clements decision: “This is not to say that new situations will not raise new considerations,” she wrote. “I leave for another day, for example, the scenario that might arise in mass toxic tort litigation with multiple plaintiffs, where it is established statistically that the defendant’s acts induced an injury on some members of the group, but it is impossible to know which ones.”

This would appear to invite an expansion of exceptions to the general “but for” test, an invitation that the plaintiff side class action bar will no doubt take up with delight.

The Outcome in Clements

The Supreme Court ultimately found the trial judge had erred in two respects. First, he should not have insisted that scientific reconstructive evidence was a necessary condition of finding “but for” causation. Second, he should not have applied the “material contribution to risk” test because the case did not fall within the exceptional circumstances that allow for its use.

The Supreme Court ordered that the case pr
oceed to a new trial, directing that Joseph Clements’ actions be assessed on the basis of the “but for” test for causation.

The word obiter comes from the Latin expression obiter dictum, which means “said in passing.” It refers to judicial remarks that are not directly related to the court’s final decision.