Mrs Clements was injured when the motorcycle driven by her husband (the defendant) span out of control after a nail punctured its rear tire. The evidence showed that Mr Clements was driving too fast and that the motorcycle was overloaded. The plaintiff claimed that she would not have been injured but for her husband’s negligence and, in the alternative, that ‘special circumstances’ warranted the application in her favour of the material contribution (MC) test from Resurfice Corp v Hanke, 2007 SCC 7. The defendant argued that the ‘but for’ onus had not been satisfied and presumably that MC did not enter into it.

At trial Grauer J was not satisfied that, but for the excessive speed and load, the defendant would have retained control of the motorcycle; it was impossible to determine the weight and speed at which the defendant would have been able to do so. The trial judge turned to the MC test and concluded on that basis that the defendant was 100% liable.

The BC Court of Appeal allowed the defendant’s appeal, noting that the MC test is one for legal – not factual – causation. Resurfice did not intend MC to displace the ‘but for’ test, which remains the default rule. The MC test is available only in the ‘special circumstances’ where it is impossible to prove ‘but for’ causation and where there is a clear breach of a duty. This will arise only in two situations: (1) circular causation (where it is impossible to say which of two parties caused the injury) or (2) dependency causation (where causation depends on establishing what one party would have done had another party not acted negligently, which may be impossible to prove). These will be rare cases; ‘but for’ remains the default rule, except where denial of liability under it would offend basic notions of fairness and justice.

The SCC has (7-2) has allowed the appeal, ordering a new trial. McLachlin CJC, for the majority, held that once the breach of a duty of care has been established, the basic rule for determining whether that breach was the cause of injury is the ‘but for’ test, which is to be applied ‘in a robust common sense fashion’, without the need for scientific evidence of the precise contribution made by the negligent defendant. The MC test, which permits a plaintiff to recover where ‘but for’ causation cannot be established, is available only in rare circumstances where fairness would require it, and generally only in situations involving multiple tortfeasors. On that basis, the trial judge made two errors: (1) he insisted on scientific evidence reconstructing the circumstances of the accident in order to find ‘but for’ causation, which was excessive; and (2) he applied the MC test to a case where it was clearly unwarranted. LeBel and Rothstein JJ, dissenting, agreed with the Chief Justice on the law, but didn’t think ‘but for’ causation could be established on the facts, even if the trial judge had used the common-sense approach to it. The trial judge was wrong to apply the MC test, but it was also wrong, on policy and process grounds, to order a new trial when the decision of the BC Court of Appeal could simply be upheld.

[Link available here].