Clarity into Causation: The SCC Articulates the Standard in Clements v Clements

In true McLachlin fashion, the Chief Justice brought clarity and consensus to a highly disputed element of the law in the recent decision, Clements v Clements, [2012] 2 SCR 181 [Clements]. Caselaw related to causation, the element in negligence actions that is often most confusing, was synthesized by the Supreme Court of Canada. The Court further provided  a two-stage test. Events do not happen in a vacuum: they sometimes comprise a series of events; and they sometimes involve multiple actors. This makes pinpointing the cause of injury in a legal setting quite difficult, or it did – until June 29th when this decision was rendered.

Students studying torts, rejoice! The highest court came to a unanimous decision as to when it is appropriate to use the standard “but-for” test for causation analysis and when it is appropriate to use the less onerous “material contribution” test (the judges all agreed on the test; two justices dissented on a separate point – whether the issue should be sent for a retrial). Chief Justice McLachlin’s two-stage test defeats the need for a painstaking assessment of which of the two tests is most appropriate for causation.


Mr. Clements (“C”) was driving his motorcycle with his wife in the passenger seat. The motorcycle at the time was 100 lbs. overloaded, and at the time (and unbeknownst to C), the rear tire was punctured by a nail. As C passed a vehicle on the road, driving 120 km/h on a 100 km/h road, the nail fell out causing air to escape the tires. Understandably, the drive became rather wobbly. Mrs. Clements consequently fell off and sustained brain injuries. She then sued C for negligence as he was speeding on an overloaded bike.

In a standard negligence claim, the plaintiff must prove on a balance of probabilities that the defendant owed a duty of care to the plaintiff, the defendant breached their duty of care, the plaintiff suffered damages and that defendant’s breach of duty caused the plaintiff’s damages. Here, there was little dispute with respect to duty of care, the breach or the injury suffered. At issue was whether the defendant actually caused the plaintiff’s injuries.

The trial judge found that, by no fault of her own, the plaintiff was unable to prove on a balance of probabilities that C’s actions caused her injuries under the “but for” test, due to the limitations of fact-finding, i.e. scientific reconstruction evidence. Instead, the trial judge applied the less onerous material contribution standard to find C liable. On appeal, the court set aside the judgement and dismissed the action. The “but for” causation element had not been proved and it was inappropriate in these circumstances to apply the material contribution test.

Causation Causing Trouble

The legal issue on appeal was whether the usual “but for” test for causation in a negligence action applies or whether the less burdensome material contribution test can be used. In answering this question, the Supreme Court of Canada provides clarity in navigating the murky waters of causation. Causation is the element of a negligence action that links the defendant’s breach of the standard of care to the plaintiff’s loss – that is, it must be shown that the defendant’s negligence caused the injury. The standard test that is used for causation is the “but for” test: the injury would not have occurred but for the defendant’s conduct. While there may be a slew of factors that contribute to the defendant’s injury, common sense is set to guide our reasoning. Common sense is not a proper guideline. Moreover, the test for causation becomes more muddled when the court introduced the “material contribution” test as a substitute for “but for” in special circumstances. The material contribution test is only to be used when it is impossible to say that a particular defendant’s negligent act caused the injury in the context of multiple tortfeasors. If this leaves you scratching your head, you’re not alone.

The Rules and the Application

The Court provided two clear guidelines in this decision. First, they held that, in general, the plaintiff may only succeed if s/he can prove on a balance of probabilities that the injury would not have ensued but for the negligent act(s) of the defendant. is not necessary that scientific causation be established. Essentially, a trial judge ought to first look to the but for test.

The second holding concerns the exception – when the court may defer to the material contribution test. The court first clarifies that the plaintiff must show that the defendant’s conduct materially contributed to the risk of injury. In general, material contribution applies when there are multiple defendants and the plaintiff can establish that but for the negligence of one or more of the defendants, the injury would not have occurred.  It was one of the defendants, but by no fault of the plaintiff, she cannot establish which one actually caused the injury. It would defy principles of fundamental fairness if both negligent defendants place blame on each other, leaving the innocent victim without compensation. That is a fancy way of saying, it would be unfair if the two defendants could just point their finger at the other and say, “it wasn’t me it was him” leaving the victim with no one to blame (on a balance of probabilities). These conditions were not present in the Clements case, so the but for test is the appropriate test.

In case the court was not being clear enough, the Chief Justice summarizes the law on causation at paragraph 46:

  1. As a general rule, a plaintiff cannot succeed unless she shows as a matter of fact that she would not have suffered the loss “but for” the negligent act or acts of the defendant.  A trial judge is to take a robust and pragmatic approach to determining if a plaintiff has established that the defendant’s negligence caused her loss.  Scientific proof of causation is not required.
  2. Exceptionally, a plaintiff may succeed by showing that the defendant’s conduct materially contributed to risk of the plaintiff’s injury, where (a) the plaintiff has established that her loss would not have occurred “but for” the negligence of two or more tortfeasors, each possibly in fact responsible for the loss; and (b) the plaintiff, through no fault of her own, is unable to show that any one of the possible tortfeasors in fact was the necessary or “but for” cause of her injury, because each can point to one another as the possible “but for” cause of the injury, defeating a finding of causation on a balance of probabilities against anyone.

Chief Justice McLachlin held that the trial judge erred in two respects: first with respect to his insistence on scientific reconstruction evidence being a prerequisite for “but for” causation; second with respect to his application of a material contribution test. Because there was only a single defendant case, the trial judge should have sidestepped the issue of scientific reconstruction evidence and should have applied the but for test. Contrary to Justices LeBel and Rothstein, the majority held that there should be a new trial to determine whether the plaintiff could indeed satisfy the burden of proof needed in the “but for” test.

The dissenting judges, Justice LeBel and Rothstein, could not find a basis for the “but for” test at all, as applied by the trial judge. The trial judge could not have inferred that the overloading of the motorcycle and excessive speed were the causes of the accident. In light of finality and efficiency in the civil litigation process, they found it is unnecessary to send the case back to trial. When it is appropriate – and justices LeBel and Rothstein found this case to be appropriate – the court should try to avoid sending issues back for retrial. Otherwise, they run the risk of expensive and drawn out appeals.

Clarity for Whom

This decision provides clarity for lawyers, jurists, professors and students. It could be said that this case, Clements, lent itself to a forward-looking decision. Ironically, the ruling creates more uncertainty for the Clements themselves. The majority concluded that the case will be retried using the “but for” test. So the only two who do not know where they currently stand in the world of causation are the very parties involved.

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