The Supreme Court takes another stab at the application of the “material contribution“ test: Clements v. Clements and the law of proof of causation in negligence

8 minute read
01 July 2012


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 resulting harm has been recognized to anchor the law of negligence to one of its underlying purposes, that of corrective justice. 

The long standing test applied by the Canadian Courts to the proof of causation is the “but for” test.  Applied in both single cause as well as multi-cause injuries, the test requires the plaintiff to demonstrate that “but for” the defendant’s negligent act, the injury would not have occurred.  However, the Supreme Court of Canada has ruled in the past that 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 the case of Clements v. Clements 2012 SCC 32 (“Clements”), the Supreme Court on the one hand narrowed the application of the “material contribution” test, but in obiter comments, suggested that the test’s application may be expanded in the future.  

The Clements Case

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

The Trial Judge found Mr. Clements’ negligence had contributed to Mrs. Clements’ injury. In finding liability, he used a “material contribution to risk” test for causation as opposed to the usual “but for” test.  He felt that on an evidentiary basis, Mrs. Clements could not establish that her injuries would not have occurred “but for” Mr. Clements’ negligence in overloading the motorcycle and driving too quickly.  As it was only, “through no fault of her own” that Mrs. 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.  Mrs. Clements was therefore successful at trial. 

The case was appealed to the British Columbia Court of Appeal where the judgment against Mr. Clements was set aside.  It was 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 then appealed to the Supreme Court.

The Supreme Court’s Decision

The central issue before the Supreme Court was in what type of exceptional circumstances may a Court apply the “material contribution” test, in place of the “but for” test of causation.  This issue required some clarification, following previous cases of the highest Court, including Resurfice Corp v Hanke [2007] 1 SCR 333 (“Resurfice”), Athey v. Leonati [1996] 3 SCR 458 and Snell v. Farrell [1990] 2 SCR 311, dealing with circumstances in which the traditional “but for” test for causation might be departed from.

In Clements, the Supreme Court was unanimous in concluding that a “material contribution to risk” test was not applicable on the facts.  The Supreme 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:

  1. It is “impossible” for the plaintiff to prove causation on the “but for” test; and
  2. It is clear that 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”. In doing so, the Supreme 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 that 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,  as 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 straight forward 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.

An interesting comment is made in obiter by Chief Justice McLachlin at paragraph 44 of the Clements decision:

This is not to say that new situations will not raise new considerations.  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 which will doubtless be taken up with delight by the plaintiff-side class action bar.

The Outcome in Clements

The Supreme Court ultimately found the Trial Judge had erred in two respects, namely (i) he should not have insisted that scientific reconstructive evidence was a necessary condition of finding “but for” causation and (ii) he should not have applied the “material contribution to risk” test because the case did not fall within the exceptional circumstances which allow for its use.  The Supreme Court ordered that the case proceed to a new trial, with the direction that Mr. Clements’ actions should be assessed on the basis of the “but for” test for causation.


Clements reinforces that the test for proof of causation in negligence remains the “but for” test, and that exceptions to its application will be few.  The Supreme Court suggests that the “material contribution ” ought to be applied only in cases of multiple concurrent tortfeasors, or in other very limited circumstances.

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