Clements v. Clements, [2012] S.C.J. No. 32 – A Case Analysis

This recent decision from the Supreme Court of Canada addresses the issue of causation for the tort of negligence.

Historically, it is required that a Plaintiff demonstrate that “but for” the negligent act of the Defendant the injury would not have occurred. Complications with the ability to draw a direct line of causation between the Defendant’s action and the Plaintiff’s injury have resulted in sometimes allowing a less onerous test to be applied. This less onerous test is that the Defendant “materially contributed to the risk of injury”.

In the Clements’ decision, the trial level judge determined that the Plaintiff did not have sufficient scientific evidence to demonstrate that her injury would not have occurred but for the Defendant’s actions. However, the trial judge determined that this was because scientific evidence is not sufficiently advanced and therefore the material contribution test should apply. Specifically, this case determines when it is appropriate to substitute the material contribution of risk test for the “but for” test.


The Defendant, Mr. Clements, was driving a motorcycle with the Plaintiff, Mrs. Clements riding behind on the passenger seat, on the highway in wet weather. Neither party were aware that a nail had punctured the bike’s rear tire. Mr. Clements had overloaded the bike by 100 pounds and was speeding to pass another vehicle when the nail came out of the tire, causing the tire to deflate. Mr. Clements lost control of the bike resulting in the bike crashing and the Plaintiff being thrown from the bike which resulted in a traumatic brain injury.


When is it appropriate to apply the material contribution to risk of injury test instead of the “but for” test in order to determine causation of negligence?


The tort of negligence requires that the Plaintiff show that the Defendant did not meet the duty of care, and the failure to do so caused the injury of the Plaintiff.

The “but for test” should always be applied to determine causation except in special circumstances. The “material contribution” to risk test requires only that the Defendant’s act contributed to the risk that the injury would occur. The variation from the “but for” test must be for the purpose of conforming to the goals of negligence law which include: compensation, fairness and deterrence. In these cases there still must be a substantial connection between the injury and the Defendant’s negligence demonstrated by the Plaintiff.

When should the material contribution test apply

In order to apply the material contribution test, instead of the “but for” test, it must be impossible for the Plaintiff to prove causation. The law of negligence has never required scientific proof of causation; common sense inferences based on the proven facts is sufficient. Therefore, as scientific evidence of causation is not a requirement, the absence of scientific evidence does not make showing causation with the “but for” test impossible and the material contribution test should not be substituted.

Actual impossibility of demonstrating legal causation includes scenarios where there is more than one possible cause of the injury. For example, when there are multiple Defendants who have breached the standard of care it may be impossible to show causation of one specific Defendant to the injury. All Defendants may suggest that injury would still have occurred because of the negligent actions of the other Defendant(s). Therefore, in cases involving multiple Defendants, it is impossible to show causation using the “but for” test and it is appropriate to apply the material contribution to risk of injury test.


The general rule in Canada is that the trial judge should take a robust and pragmatic approach to determining if a Plaintiff has established that the Defendant’s negligence caused a loss. In exceptional circumstances, a Plaintiff may only have to show that the Defendant’s conduct materially contributed to the risk of the Plaintiff’s injury, if they can demonstrate that:

(a) the loss to the Plaintiff would not have occurred “but for” the negligence of two or more tortfeasors, and

(b) it is impossible for the plaintiff, through no fault of her/his own, to show that any one of the possible tortfeasors was the necessary “but for” cause of her injury.


The Clements case does not present the impossibility of the “but for” test succeeding. At trial, the judge determined that the Plaintiff was not able to show solid scientific evidence that the injury suffered would not have occurred “but for” the negligent actions of overloading the motorcycle and speeding. The trial judge found that because of this “impossibility” the material contribution to risk test should be applied. The law requires a “robust and pragmatic approach to the ‘but for’ test. The judge should have allowed for the possibility that without the use of scientific proof, the negligence of the Defendant could be shown to have caused the injury of the Plaintiff.

Therefore, causation is not impossible to demonstrate using the “but for” test and the material contribution test should not be applied.

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