With the end approaching of what would have been, once upon a time, the “long vacation” and litigators gearing up for the fall court season, it’s time for a fashion tip reminder.
The reminder is that is is no longer the law in common law Canada that, somehow, the but-for test is to be applied differently in civil cases where expert evidence is adduced on the issue of factual causation, even in those places where it was once fashionable to assert it was; even in those places in common law Canada where some seem to think it is still in fashion to assert it is.
From Russell Brown,* “Cause-in-Fact at the Supreme Court of Canada: Developments in Tort Law in 2012-13″ (2014), 64 S.C.L.R. (2d) 327 at 352
(* now a Justice of the Alberta Court of Appeal and Honorary Professor of Law at the University of Alberta; Justice of the Court of Queen’s Bench of Alberta at the time of publication)
To appreciate this statement’s significance, it must be understood that the defendant had relied, at the Court of Appeal (and in his factum, but not in his oral submissions, at the Supreme Court), on appellate authority in British Columbia precluding the drawing of a causal inference where the defendant introduces expert evidence that cause-in-fact does not exist.  The Court of Appeal had applied this rule in Ediger (Guardian ad litem of) v. Johnston,  where the defence had led such evidence disputing cause-in-fact, and offering alternative explanations for the umbilical cord compression, such as a kink or a nuchal cord. Given that context, the Supreme Court’s statement appears to reassert the point from Snell that finding cause-in-fact is a matter of drawing inferences from the evidence, rather than waiting to be led to the “correct” answer by an expert. An inference of cause-in-fact may be drawn (or not drawn) in all situations — that is, irrespective of whether there is expert evidence in only one direction, both directions, or no direction.85 The plaintiff’s burden is to prove cause-in-fact to a balance of probabilities. The mere fact that the defendant adduces expert evidence opining that cause-in-fact does not exist does not oust the fact-finder’s role, but simply requires the fact-finder to weigh that evidence against the plaintiff’s and determine whether the plaintiff has met her burden.
83. Sam v. Wilson, [2007 BCCA 622] supra, note 26, at para. 144, citing Moore v. Castlegar & District Hospital,  B.C.J. No. 332, 49 B.C.L.R. (3d) 100, at para. 11 (B.C.C.A.): “With respect, I think in a case like this where there is affirmative medical evidence leading to a medical conclusion it is not open to the court to apply the common sense reasoning urged in Snell v. Farrell.”
84.  B.C.J. No. 974, 333 D.L.R. (4th) 633, at para. 83 (B.C.C.A.).
“The “robust and pragmatic” approach to the analysis of evidence adopted in Snell, which permits an inference of causation to be drawn in certain circumstances, is not applicable where evidence to the contrary on a plaintiff‟s theory of causation is tendered.”
[Emphasis in bold added.]
“This statement”, in the Brown article, refers to the following passage in Ediger v. Johnston, 2013 SCC 18,  2 S.C.R. 98, at para. 36, per Rothstein and Moldaver JJ.:
The Court of Appeal‟s reasons also suggest that it understood the trial judge to have improperly relied on Snell v. Farrell,  2 S.C.R. 311, in order to draw an “inference of causation” (paras. 83-85). Snell stands for the proposition that the plaintiff in medical malpractice cases — as in any other case — assumes the burden of proving causation on a balance of the probabilities (ibid., at pp. 329-30). Sopinka J. observed that this standard of proof does not require scientific certainty (ibid., at p. 328); Clements, at para. 9. The trier of fact may, upon weighing the evidence, draw an inference against a defendant who does not introduce sufficient evidence contrary to that which supports the plaintiff‟s theory of causation. In determining whether the defendant has introduced sufficient evidence, the trier of fact should take into account the relative position of each party to adduce evidence (Snell, at p. 330). 
82. Ediger, supra, note 2, at para. 36.
The most recent reported reiteration of the error, as of writing, occurred in Briante v. Vancouver Island Health Authority, 2014 BCSC 1511:
 It is clear that causation cannot be inferred particularly where the defendants have called evidence on causation. Moore v. Castlegar & District Hospital, [1998 CanLII 4906], (1998), 49 B.C.L.R. (3d) 100; Borglund v. Fraser Valley Health Region, 2006 BCSC 1338.
With one one-time, seemingly aberrant, exception, the Moore v. Castlegar error seems to have been unique to British Columbia.
In for a penny, etc: since I’ve decided to bite hands, so to speak, out here too, let’s ask ourselves this question. What does it mean to claim that “causation cannot be inferred” or, translating what this statement seems to assert “that causation cannot be decided by inference”? If “inference can’t be used, how does the causation decision get made at all? By some sort of axiomatic (i.e., deductive, in its literal sense) process? By judicial notice, only?
Bear in mind that the “causation” decision presupposes a multitude of factors none of which the judge actually decided. These include: the existence of the universe; the local cluster; the galaxy; the solar system; the principles of classical physics; the road existed; the vehicles existed; the plaintiff had been born; the plaintiff was a human being; that the plaintiff was living at all relevant times etc. All of these issues, if the judge were to instruct herself or himself that the issues had to be decided, would be determined by inference(s), in part at least.