Clements (Litigation Guardian of) v Clements: The SCC Takes Another Crack at Material Contribution

If you speak to first year law students, many will tell you that the doctrine of material contribution is perhaps the most ambiguous aspect of Canadian tort law. The Supreme Court of Canada has an opportunity to clarify the material contribution test when it releases its decision in Clements (Litigation Guardian of) v Clements, which the court heard on February 17th. The case has been appealed from a judgment of the British Columbia Court of Appeal.

The appellant in the case, Joan Clements, was severely injured when she was thrown from a motorcycle being driven by the respondent, her husband Joseph Clements. Mr. Clements lost control of the vehicle when the back wheel was punctured by a sharp object, causing it to rapidly deflate. Despite his best efforts to maintain control, the motorcycle capsized and flipped over, throwing off both passengers.

Mrs. Clements brought a claim in negligence against her husband. The trial judge held that he was negligent (had breached his duty of care) in two respects. Firstly, the motorcycle was overloaded, and secondly, it was being driven at excess speed. However, it was unclear whether Mr. Clements’ carelessness actually caused the harm that occurred or whether the motorcycle would have capsized in any event. Therefore, the case turned on the issue of causation.

Causation in Tort Law

The default test for causation in tort law is known as the “but for” test. This simply asks, “but for the negligent conduct, would the harm have occurred?” In other words, was the negligent conduct a necessary condition for the harm to occur? The application of this test is illustrated in the English case of Barnett v Chelsea & Kensington Hospital Management Committee, [1968] 1 All ER 1068. In this case, the plaintiff drank contaminated tea and became ill. He was admitted into a hospital, where he was negligently treated and discharged. He died five hours later of arsenic poisoning. The hospital was not held liable, however, as the trial judge held that even if the plaintiff had been admitted and treated appropriately he still would have likely died in any event due to the rapid onset of the poison.

The “but for” test may be commended for its simplicity. However, simplicity can also be its downfall in more complex cases where there are multiple potential causes for a harm and where the degree to which each potential cause contributed to the harm is unclear. “Material contribution,” therefore, exists as an alternative to “but for” in order to hold a defendant liable in tort when they materially contributed to the harm (or risk of harm) the plaintiff suffered.

The Supreme Court of Canada addressed the doctrine of material contribution in Athey v Leonati, [1996] 3 SCR 458, in which Major J stated:

The “but for” test is unworkable in some circumstances, so the courts have recognized that causation is established where the defendant’s negligence “materially contributed” to the occurrence of the injury: . . . A contributing factor is material if it falls outside the de minimus range. (para 15)

Athey upheld the supremacy of the “but for” test, while also recognizing its potential shortcomings and allowing for the application of the material contribution test in certain circumstances. However, the case did little to explain when “but for” becomes unworkable or what it means to “materially contribute” to a harm (beyond the cryptic “beyond de minimus range”).

These questions were addressed to some extent when material contribution resurfaced (pun intended) before the court in Resurfice Corp v Hanke, [2007] 1 SCR 333, where the court held as follows:

In special circumstances, the law has recognized exceptions to the basic “but for” test, and applied a “material contribution” test. Broadly speaking, the cases in which the “material contribution” test is properly applied involve two requirements. (Para 24)

First, it must be impossible for the plaintiff to prove that the defendant’s negligence caused the plaintiff’s injury using the “but for” test. The impossibility must be due to factors that are outside of the plaintiff’s control; for example, current limits of scientific knowledge. Second, it must be clear that the defendant breached a duty of care owed to the plaintiff, thereby exposing the plaintiff to an unreasonable risk of injury, and the plaintiff must have suffered that form of injury. In other words, the plaintiff’s injury must fall within the ambit of the risk created by the defendant’s breach. In those exceptional cases where these two requirements are satisfied, liability may be imposed, even though the “but for” test is not satisfied, because it would offend basic notions of fairness and justice to deny liability by applying a “but for” approach. (Para 25)

Hanke clarified therefore, that material contribution may only be applied in the “special circumstances” where: (1) it is impossible to prove that the defendant’s negligence caused the plaintiff’s injuries using the “but for” test, and the impossibility is due to factors outside of the plaintiff’s control, and (2) it is clear that the defendant breached a duty of care to the plaintiff, thereby exposing the plaintiff to an unreasonable risk of injury, and that the plaintiff did suffer that form of injury.

This test from Hanke remains the material contribution test that has been applied by courts to today, and was the one applied by the trial judge in Clements.

The Decision at Trial

The trial judge in Clements held that the case fit the special circumstances referred to in Hanke and thus the “but for” test was unworkable. Accident-reconstruction modeling was not able to offer conclusive evidence as to whether, but for the excess weight and speed of the motorcycle, Mr. Clements would have been able to recover from the weave instability caused by the punctured tire. Therefore, it was impossible to prove that the defendant’s negligence caused the plaintiff’s injuries using “but for” and the impossibility is due to factors outside of the plaintiff’s control. At the same time, based on the findings that the motorcycle was overloaded and travelling at excess speed, it was clear that the defendant breached a duty of care to the plaintiff, thereby exposing the plaintiff to an unreasonable risk of injury. Finally, the plaintiff, Mrs. Clements, did suffer a severe injury as a result of the accident.

The trial judge then applied the material contribution test, and held that the excess speed and overloading of the motorcycle materially contributed to the injuries suffered by the plaintiff.

The Decision at the British Columbia Court of Appeal

The trial judge’s decision appeared to be a valid application of the principles laid down in Hanke as to when and how material contribution should be applied. However, the Court of Appeal overturned the decision, holding that the case was not an appropriate one for the application of the material contribution test and should have been dismissed once the plaintiff failed to satisfy causation under the “but for” test.

In essence, the Court of Appeal sought to limit the cases to which the “special circumstances” that allow the application of the material contribution test apply. The court looks to the 2010 article, “Clarifying Causation in Tort,” by Professor Erik S. Knutsen, to identify the two situations, referred to as “circular causation” and “dependency causation,” in which the material contribution test may be applied.

Circular causation refers to a scenario where “the “but for” test makes it impossible to determine which of two negligent parties caused the damage suffered by the plaintiff” (para 55). The classic example of this is the case of Cook v Lewis, [1951] S.C.R. 830, in which two defendant hunters negligently fired at the plaintiff, but it could not be proven whose buckshot struck the plaintiff and caused his injuries.

Dependency causation, meanwhile, occurs “where proof of factual causation depends on establishing what one party would have done if another party had not acted in a negligent manner, something which may be impossible to prove” (para 56). An example of this is Walker Estate v York Finch General Hospital, [2001] 1 SCR 647, in which the plaintiff contracted HIV from blood supplied by the Canadian Red Cross Society, who had been negligent in donor screening. The court held that, since it was uncertain whether an appropriately warned infected donor would have proceeded to donate blood anyway, the plaintiff could not prove causation using “but for” and “material contribution” could be applied.

In Hanke, the court referred specifically to each of Cook and Walker in describing appropriate cases for the application of the material contribution test. The B.C. Court of Appeal in its decision sought to further limit the application of the test to these particular types of cases. It reasons that this is essential to ensure the supremacy of the “but for” test and limit the application of material contribution to cases where it truly “offends basic notions of fairness and justice” (para 63) and is not merely a “solution for evidentiary insufficiency” (para 58). Applying this reasoning to the Clements case, the Court held that this was neither a case of circular nor dependency causation, and allowed the appeal.


While Hanke has been helpful in clarifying when material contribution may be applied, it has been subject to criticism, for being too vague as to what “special circumstances” refers to. Perhaps in recognition of this criticism, the B.C. Court of Appeal has sought to clarify with more precision what circumstances are special enough for the test to be applied — instances of circular and dependency causation. Limiting the scope of circumstances to which a defendant may be held liable in tort is generally a good thing, as it may help Canada avoid the tort litigation quagmire that bogs down courts in the United States. However, at the same time, it may leave victims of tragic accidents without compensation due to evidentiary shortcomings. In deciding this case, the Supreme Court has an opportunity not only to clarify the ambiguous material contribution doctrine but also to take a stance on the relative weights that ought to be placed on tort law’s twin goals of compensation for accident victims, and punishment and deterrence for potential tortfeasors.

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