MAY now do; for general causation in class actions, too.
see Bartram v. GlaxoSmithKline Inc., 2012 BCSC 1804 at para. 32:
 In an individual action, a plaintiff probably could not succeed by merely showing that the use of Paxil increased the risk of injury. In Clements v. Clements, , 2012 SCC 32, the Supreme Court of Canada re-affirmed the primacy of the “but for” test in proving causation and confined the alternate “material contribution” test to cases involving multiple negligent defendants where it is not possible to prove which one caused the injury. However, dicta in Clements may leave open an argument that different considerations apply in cases involving multiple plaintiffs, such as class actions.
‘ 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.’”
“Too” because the premise of the Clements material contribution to risk test is that while the the negligence of least one one of the group of two or more negligent persons who whose conduct is found to be a legal cause was, in fact, a factual cause, it is also the case that the negligence of at least one of that group was not, in fact, a factual cause. Again, this is because the premise of Clements material contribution to risk test is that the causal candidates are alternative, not cumulative.
Some scholars in the large scale “toxic torts” field call this “aggregate causatation”. See, for example, Craig Jones, “Reasoning Through Probabilistic Causation in Individual and Aggregate Claims: The Struggle Continues” (2011) 39 Adv. Q. 18; Lynda M. Collins “Causation, contribution and Clements: Revisiting the material contribution test in Canadian tort law” (2011), 19 Tort L. Rev. 86; and Lynda M. Collins and Heather McLeod-Kilmurray, “Material Contribution to Justice? Toxic Causation after Resurfice Corp v. Hanke” (2010) 48 Osgoode Hall L.J. 411
Those who practice in the class action field might ask themselves this question. If possibility is enough for both general causation and specific causation, how likely is it that the class will ever fail to satisfy the causation requirement at the certification motion?