The test for causation in Canada: but for, but ... maybe not.

• Author: Lawrie, Jill

PRIOR to Canada's Supreme Court decision in Resurfice Corp. v. Hanke, (1) there was significant confusion (and significant controversy) over the accurate statement of the causation test in Canada. Despite the apparent attempt to put an end to both the confusion and the controversy, it is the authors' view that the decision has done little to clear up the confusion and, judging by the volume of commentary on the decision, has only fueled the controversy. On its face, the decision sets out a straightforward rule that the primary test for causation remains the "but for" test and allows for exceptions to that rule only in "special circumstances." In this paper, we will review the significant causation decisions of the Supreme Court of Canada leading up to Resurfice, review the "clarification" outlined in the decision, and conclude that there are still significant unsettled issues in the law of causation in Ontario.

1. Background

   There are a number of very thorough academic analyses of the evolution of the law of causation generally and of the effect of Resurfice in particular. Some of the commentators on Resurfice suggest that the decision has made it easier to establish causation, some say it is now harder to establish causation and some say it has not changed the law at all. (2) It is not yet clear which of these commentators will prove correct in Ontario. To date, the Ontario Court of Appeal has steered clear of grappling with the exceptions to the primary test and has held fast to the "but for" test for causation. It will be interesting to see how the exceptions are treated when a "special circumstances" case comes before that Court.

   1. Causation

      To start with the obvious (and the least controversial), causation is used by courts to determine whether a particular defendant can and should be held liable to a particular plaintiff. According to the Supreme Court of Canada, "Causation is an expression of the relationship that must be found to exist between the tortious acts of the wrongdoer and the injury to the victim in order to justify compensation of the latter out of the pocket of the former." (3)

      In products liability cases, as with all negligence cases, assuming the other elements of negligence have been established, the plaintiff bears the burden of proving, on a balance of probabilities, that the act or omission constituting the negligence of the manufacturer, distributor or retailer of the product caused the plaintiff's injuries. If the plaintiff fails to prove causation, the products liability claim necessarily fails.

   2. The "But For" Test

      The "but for" test can be simply and precisely articulated: A plaintiff must prove, on a balance of probabilities, that but for the negligence of the defendant, the plaintiff's injury would not have occurred. The "but for" test was cemented into Canadian causation law by the Supreme Court of Canada in 1972. (4)

   3. The Material Contribution Test

      In 1996, Athey v. Leonati launched confusion and controversy over what has been described as the "material contribution" test. (5) Unlike the "but for" test, the material contribution test eludes precise articulation.

      Mr. Athey had suffered from minor back problems since 1972 and was injured in two motor vehicle accidents in 1991. These accidents occurred within two months of each other. Some months after the two motor vehicle accidents, Mr. Athey's condition improved and his physician suggested that he try to resume his regular exercise routine. While stretching during a warm up at the gym, the plaintiff heard a "pop" in his back, and by the next morning he was unable to move. Mr. Athey was diagnosed with a disc herniation and sustained serious, long lasting injuries. The question was whether the motor vehicle accidents that were the subject of the lawsuit caused the plaintiff's injury. The Supreme Court of Canada was faced with a trial decision in which the trial judge approached the matter without correctly distinguishing between the test for causation and the test for apportionment of liability between tortious causes. The trial judge held that the injuries suffered in the motor vehicle accidents contributed to some degree [25%] to the disc herniation and thus awarded the plaintiff 25% of the global damages claimed.

      The Court stated:

      ... The competing causes in this case were the injuries sustained in the accidents and a pre-existing disposition to back problems.

      The applicable principles can be summarized as follows. If the injuries sustained in the motor vehicle accidents caused or contributed to the disc herniation, then the defendants are fully liable for the damages flowing from the herniation. The plaintiff must prove causation by meeting the "but for" or material contribution test. Future or hypothetical events can be factored into the calculation of damages according to degrees of probability, but causation of the injury must be determined to be proven or not proven. This has the following ramifications:

1. If the disc herniation would likely have occurred at the same time, without the injuries sustained in the accident, then causation is not proven.

2. If it was necessary to have both the accidents and the pre-existing back condition for the herniation to occur, then causation is proven, since the herniation would not have occurred but for the accidents. Even if the accidents played a minor role, the defendant would be fully liable because the accidents were still a necessary contributing cause.

3. If the accidents alone could have been a sufficient cause, and the pre-existing back condition alone could have been a sufficient cause, then it is unclear which was the cause-in-fact of the disc herniation. The trial judge must determine, on a balance of probabilities, whether the defendant's negligence materially contributed to the injury. (6)

   It is not obvious the statement in item 3 suggests anything other than that the trial judge still had to decide whether, on a balance of probabilities, 1 or 2 applied on any particular facts. It is not at all obvious that the Court intended to create or did create a new test in item 3; that is, that a "sufficient" cause is different from a "necessary" cause. On strict examination, the statement may simply be interpreted to stand for the proposition that a cause is sufficient only if it is necessary, especially given that Court's ultimate finding referencing "necessary ingredients."

   Regarding the analysis of the trial judge, the following is a summary of the Court's observations:

1. If the trial judge meant that there was a 25% chance that the injury was caused by the accidents, and a 75% chance that it was caused by the pre-existing condition, then causation would simply not be proven.

2. The findings of the trial judge indicate that it was the combination of the pre-existing condition and the injuries sustained in the accidents that caused the herniation. Although the accidents played a lesser role than the preexisting problems, the accidents were nevertheless a necessary ingredient in bringing about the herniation.

3. A 25% contribution falls outside the de minimus range and was therefore a material contribution and sufficient to render the defendant fully liable for the damages flowing from the disc herniation. (7)

   What is clear from this decision is that the "material contribution test" is not a test that assesses the chance that an act or omission contributed to the injury; that in order to be a material contribution, an act or omission has to be found, on the balance of probabilities, to be a necessary ingredient to the occurrence of the injury; and that...