The majority, led by McLachlin C.J., expounded on the material contribution test, and indicated that it is better characterized as a “material contribution to risk” and not to injury. However, this approach should be rarely used to ensure that the fundamental principles of tort law for proof of causation are not undermined.
The court also clarified the principle found in Resurfice Corp. v. Hanke that the material contribution test is appropriate where causation under the but for test is impossible to prove,
 Some have suggested that “but for” proof must be logically or conceptually impossible before material contribution to risk is available… Clearly the impossibility in those examples was related to difficulties with factual proof, not to logical problems inherent in the peculiarities of the case.
 However, the option of finding that a material contribution to risk approach is available whenever proof of “but for” causation cannot be made on the facts is equally problematic. First, how does one distinguish between a case of true impossibility of factual proof and a situation where the plaintiff simply fails to meet her burden of establishing “but for” causation on the evidence? Unless one can make a clear distinction, one effectively undermines the requirement that the plaintiff bears the burden of showing that, “but for” the defendant’s negligence, she would not have been injured. In any difficult case, the plaintiff would be able to claim impossibility of proof of causation. Such a result would fundamentally change the law of negligence and sever it from its anchor in corrective justice that makes the defendant liable for the consequences, but only the consequences, of his negligent act.
The impossibility referred to in case law does not describe scientific impossibility, but rather the impossibility to determine on a balance of probabilities which specific tortfeasor was at fault. The material contribution test achieves fairness in compensation because the plaintiff has already established a but for causation on a global scale, but is unable to determine which specific defendant was responsible for the injury.
The majority discussed the case of Sienkiewicz v. Greif (UK) Ltd.,  UKSC 10,  2 All E.R. 857, where the material contribution test was applied against a single tortfeasor, but noted that Canadian courts had difficulty applying this principle and have not adopted this approach,
 It is important to reaffirm that in the usual case of multiple agents or actors, the traditional “but for” test still applies. The question, as discussed earlier, is whether the plaintiff has shown that one or more of the defendants’ negligence was a necessary cause of the injury. Degrees of fault are reflected in calculations made under contributory negligence legislation. By contrast, the material contribution to risk approach applies where “but for” causation cannot be proven against any of multiple defendants, all negligent in a manner that might have in fact caused the plaintiff’s injury, because each can use a “point the finger” strategy to preclude a finding of causation on a balance of probabilities.
 This is not to say that new situations will not raise new considerations. I leave for another day, for example, the scenario that might arise in mass toxic tort litigation with multiple plaintiffs, where it is established statistically that the defendant’s acts induced an injury on some members of the group, but it is impossible to know which ones.
McLachlin C.J. provided a helpful summary of the present state of law at para. 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.
The dissent, written by LeBel J., agreed in substance with the majority with the law, but departed in the application in this case,
 The trial judge’s comments must be read in the context of his decision as a whole. He had determined that, in view of the impossibility of proving how, or whether, each factor had contributed to the accident, “but for” causation should be dispensed with and a “material contribution” test applied. The quoted comments were made in the context of his application of the latter test. They constituted his conclusion that the material contribution test had been satisfied.
 For the reasons given by the Chief Justice, the application of the material contribution test by the trial judge was inappropriate. Further, as the Chief Justice states, at para. 14, the “but for” and material contribution tests are “two different beasts”. The material contribution test does not require a factual inquiry into what likely happened, but imposes liability as a matter of policy. The trial judge’s finding that the material contribution test was satisfied cannot be reinterpreted as a finding that “but for” causation was established without seriously undermining the important distinction between the two tests and the clarity of the analysis pertaining to causation.