The counterfactual analysis aspect
A case worth reading, because it accurately explains how the but-for counterfactual hypothetical (i.e., possible, what-if, etc., world) analysis is to be done. (For those who have been paying attention, that’s the analysis for a test that we’ve been told isn’t metaphysical at all, which is one reason why we’re to use it rather than go adventuring with philosophers into abstract metaphysics, or something like that.)
Lee v Minister for Correctional Services,  ZACC 30, 2013 (1) SACR 213 (CC) (11 December 2012) starting at para. 37.
As a colleague put it, the court’s explanation is “far better than anything our Supreme Court has ever come up with”.
One case that isn’t helpful on the “how” of the counterfactual analysis – even if, for other reasons, the result of the case is correct: I make no comment on that point – is Eli Lilly and Company v. Apotex Inc., 2014 FC 1254 at paras. 20-35. I believe that, after you read Lee, if you read Lee, you’ll understand why the discussion in Eli Lilly isn’t helpful. And why the explanation is wrong, even if the conclusion is correct.
The how much evidence is enough aspect – i.e., the Snell robust and pragmatic inference
Judges, we know, have long memories. They talk amongst themselves. It doesn’t do a lawyer’s clients any good, let alone the lawyer’s reputation, if judges begin with the assumption counsel doesn’t know the applicable law.
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 331
(* 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)
It is worth making two observations about the drawing of a causal inference. First, there is nothing unorthodox about the proposition that a fact-finder may draw causal inferences, even in the absence of verifying scientific evidence. Inference-drawing is inherent not only in all causal fact-finding, but in all fact finding. Just as one might infer from evidence that an automobile made a screeching noise immediately prior to a collision that the driver saw the obstruction just before striking it, one may also infer (or not infer) that evidence of risk, of harm and of the surrounding circumstances is so arrayed so as to support the drawing of an inference of a causal relationship between the risk and the harm – and all without the reassurance of expert evidence. And, just as the absence of direct evidence that the driver saw the obstruction before hitting it does not preclude an inference that he or she did, the absence of direct evidence verifying a causal link between risk and harm is similarly not determinative. Fact-finders infer, or they do not infer, and they may do so on evidence that bears only indirectly to the proposition being advanced.
The second observation is that causal inference-drawing is not presented in Snell as some form of alternative or watered-down version of the but for test. If all fact-finding is necessarily inferential, then fact-finding to the but for standard is also inferential. So long as the inference is drawn on a balance of probabilities, causal inference is no alternative to the but for test, but is an instantiation of it. It is how the but for test is to be applied – and not merely in some cases, but in all cases.
 Russell Brown, “The Possibility of ‘Inference Causation’: Inferring Cause-in-Fact and the Nature of Legal Fact-Finding” (2010) 55 McGill L.J. 1, at 30-35 [Brown, “Inference Causation”].
 This was the criticism of Lewis Klar, in Tort Law, 3d ed. (Toronto: Thomson Carswell, 2003) at 403: “[w]hile [inference-drawing] may produce a pragmatic solution to a plaintiff’s dilemma in difficult causation cases, it does depart from the traditional “but for” test, and the balance of probability standard.” This statement does not appear in subsequent editions of Professor Klar’s book.
In Simmons v. Yeager Properties Inc., 2014 BCCA 201 (released on May 20, 2014 so on the BCCA website soon after that) Lowry JA ( A. MacKenzie JA and Goepel JA concurring) wrote:
 … The default framework for causation was described in Clements v. Clements, 2012 SCC 32, as follows:
 The test for showing causation is the “but for” test. The plaintiff must show on a balance of probabilities that “but for” the defendant’s negligent act, the injury would not have occurred. Inherent in the phrase “but for” is the requirement that the defendant’s negligence was necessary to bring about the injury ― in other words that the injury would not have occurred without the defendant’s negligence. This is a factual inquiry. If the plaintiff does not establish this on a balance of probabilities, having regard to all the evidence, her action against the defendant fails.
In Ediger v Johnston, 2013 SCC 18,  2 SCR 98, the unanimous (albeit “only” 7 member panel) agreed, in reasons written jointly by Rothstein and Moldaver JJ:
 This Court recently summarized the legal test for causation in Clements v. Clements, 2012 SCC 32,  2 S.C.R. 181. Causation is assessed using the “but for” test (Clements, at paras. 8 and 13; Resurfice Corp. v. Hanke, 2007 SCC 7,  1 S.C.R. 333, at paras. 21-22). That is, the plaintiff must show on a balance of probabilities that “but for” the defendant’s negligent act, the injury would not have occurred (Clements, at para. 8). “Inherent in the phrase ‘but for’ is the requirement that the defendant’s negligence was necessary to bring about the injury — in other words that the injury would not have occurred without the defendant’s negligence” (para. 8 (emphasis deleted)).
Even if the point in Ediger has been slow to make it this far west, for whatever reason, there’s now Simmons v. Yeager.
[Link updated to CanLII link – 15 Dec 2014]