Something is fishy, here (BC sockeye; Ontario carp)
The text speaks for itself, right?
Or is it that some judges are listening, but not hearing, because (metaphorically) the speakers are wearing brown shoes?
So, once upon a time, but not that long ago:
Clements v. Clements,  2 SCR 181, 2012 SCC 32, para 8:
 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.
 To recap, the basic rule of recovery for negligence is that the plaintiff must establish on a balance of probabilities that the defendant caused the plaintiff’s injury on the “but for” test. This is a factual determination. Exceptionally, however, courts have accepted that a plaintiff may be able to recover on the basis of “material contribution to risk of injury”, without showing factual “but for” causation. As will be discussed in more detail below, this can occur in cases where it is impossible to determine which of a number of negligent acts by multiple actors in fact caused the injury, but it is established that one or more of them did in fact cause it. In these cases, the goals of tort law and the underlying theory of corrective justice require that the defendant not be permitted to escape liability by pointing the finger at another wrongdoer. Courts have therefore held the defendant liable on the basis that he materially contributed to the risk of the injury.
Athey v. Leonati,  3 SCR 458 at paras. 17, 41.2, 1996 CanLII 183
 It is not now necessary, nor has it ever been, for the plaintiff to establish that the defendant’s negligence was the sole cause of the injury. There will frequently be a myriad of other background events which were necessary preconditions to the injury occurring. To borrow an example from Professor Fleming (The Law of Torts (8th ed. 1992) at p. 193), a “fire ignited in a wastepaper basket is . . . caused not only by the dropping of a lighted match, but also by the presence of combustible material and oxygen, a failure of the cleaner to empty the basket and so forth”. As long as a defendant is part of the cause of an injury, the defendant is liable, even though his act alone was not enough to create the injury…
. . .
[41.2 ] If it was necessary to have both the accidents and the pre-existing back condition for the herniation to occur, then causation is proven, since the herniation would not have occurred but for the accidents. Even if the accidents played a minor role, the defendant would be fully liable because the accidents were still a necessary contributing cause.
[underlining emphasis in original; bold emphasis added]
In passing, para. 17 of Athey isn’t quite right. It’s more than “frequently”. It’s always. The irony (?) oddity (?) of the paragraph is that the “always” point is made explicitly in the complete passage in Fleming, The Law of Torts, from which Athey took the example in para. 17.
On the other hand, recently:
Andrusko v. Alexander, 2013 BCSC 985 (Judgment: June 2013; trial: December 2012)
 The plaintiff must establish on a balance of probabilities that the defendant’s negligence caused or materially contributed to an injury. The defendant’s negligence need not be the sole cause of the injury so long as it is part of the cause beyond the de minimis range. Causation need not be determined by scientific precision: Athey v. Leonati,  3 S.C.R. 458 at paras. 13-17.
 The primary test for causation asks: but for the defendant’s negligence, would the plaintiff have suffered the injury? The “but for” test recognizes that an award of compensation for negligent conduct should be made only where a substantial connection between the injury and the defendant’s conduct is present: Resurfice Corp. v. Hanke, 2007 SCC 7 at paras. 21-23. …
Guess what case wasn’t cited. It’s the same name, repeated. CanLII helps because it lists the cases cited (where the cite is recognized by CanLII’s cite recognition program.)
Of course, in the trial judge’s defence, if she wasn’t going to cite Clements (2012), but rather Resufice (2007) then she could have (should have?) cited Farrant v. Laktin, 2011 BCCA 336 at paras. 12, 13:
 In Resurfice Corp. v. Hanke, 2007 SCC 7, 1 S.C.R. 333, the Supreme Court affirmed the “but for” test remains the basic test for determining causation, but developed the concept of “material contribution” in a different manner than that used in Athey, formulating a “material contribution” test as an exception to the “but for” test, a matter that is not relevant to this appeal. The Court replaced the Athey definition of “material contribution” to the plaintiff’s injury with the concept of “a substantial connection” between the injury and the defendant’s conduct. … These developments were usefully summarized by Mr. Justice Smith, writing for the majority, in Sam v. Wilson, 2007 BCCA 622 at para. 109:
. . .
 Thus, in applying the “but for” test, the trial judge was required to consider not just whether the defendant’s conduct was the sole cause of the plaintiff’s disabling pain, but also whether the plaintiff had established a substantial connection between the accident and that pain, beyond the de minimus level.
This passage in Farrant has been cited by other judges of the BCSC (but not the BCCA) since Clements, without mentioning Clements. See, for example: Paller v. Regan, 2013 BCSC 1672
 The plaintiff must establish on a balance of probabilities that the defendants’ negligence caused or materially contributed to an injury. The defendants’ negligence need not be the sole cause of the injury, so long as it is part of the cause beyond the range of de minimis. Causation need not be determined by scientific precision: Athey v. Leonati,  3 S.C.R. 458 at paras. 13-17, and Farrant v. Laktin, 2011 BCCA 336, para. 9.
For what it’s worth, cases like Alexander and Paller are a pain for those of us trying to keep tabs on the current (mis)state – to coin a neologism – because one can’t run a CanLII search using Clements. What you have to do is run a searches for combinations of caus*, Athey, & Resurfice but without Clements while crossing one’s fingers and dancing widdershins around a broken Sherwood goalie stick. Appropriate hockey gear is optional.
Next, crossing the mountains into the not-so-remote East:
Strangis v. Patafio, 2013 ONSC 6240
 “Caused” here does not mean “sole cause”. If the car collision materially contributed to the current situation, then that is enough. On the other hand, if the car collision did not materially contribute to the permanent damage, then Mr Strangis is in largely the same situation today that he would have been in without the car collision and he has not established causation. [fn 6]
[fn 6] See Clements v. Clements, 2012 SCC 32; Farrell v. Snell,  2 S.C.R. 311; Athey v. Leonati,  S.C.R. 458; Resurfice Corp. v. Hanke,  1 S.C.R. 333; Dinham v. Brejkain (2005), 33 C.C.L.I. (4th) 263 (S.C.J.).
If you care:
If you decide to read the complete text of both the BCSC and ONSC reasons, ask yourself whether the misstatement of the law is relevant to the judge’s conclusion. Those of you who aren’t familiar with Ontario’s … idiosyncrasies … should keep in mind that Strangis is the text of the trial judge’s reasons on a separate issue of whether the alleged injury was sufficiently serious to meet Ontario’s threshold for actionability of injury allegedly sustained in a motor vehicle accident. It’s not the reasons for judgment in the tort action. That action was tried with a jury. What I’m asking you to do, in Strangis, is ask yourself whether, assuming the trial judge explained causation to the jury in the same way as appears in these reasons, that explanation might have affected the jury’s conclusion on damages.
The sentences in paras.  and  of Andrusko contain literally accurate statements of existing propositions of law, before Clements, but that doesn’t mean that each of the statements makes sense.
We have no idea what meaning the judge is ascribing to “materially contributed” with or without the gloss given to “materially contributed” by the BCCA.
That sentence conflates factual causation with the scope of legal responsibility. Also, if it’s understood to be connected to terms in the first sentence, it implies the judge did mean “materially contributed” in a factual causation sense. That implies a belief in degrees of necessity for factual causation.
Yeah, that’s what Snell and Athey said.
If by “causation” the judge meant all aspects of legal causation the statement is correct but incomplete. If the judge meant factual causation, the statement is literally accurate but meaningless unless one knows what the judge meant by “but for” and “suffered”. That takes us to the next sentence.
That’s not even a literally accurate recitation of what the SCC wrote in Resurfice; although it’s an accurate statement of what the BCCA wrote, and seemingly meant, in Farrant. The Resurfice passage is para. 23:
Even if one doesn’t bother to go back and read Snell to get the context of the quoted passage, because one takes the position that the SCC is never wrong in its statements about the meaning of any statement in one of its prior cases – well … at least until another panel restates that meaning in a later decision – the use of “compensation” should be a red flag that that passage isn’t focused just on factual causation, rather, is about the on the scope of legal responsibility. “Factual causation” (whatever meaning one gives that phrase”) is merely an aspect of the legal concept of causation.
Did the notion that, somehow, “change of position” is the defining, always necessary, component of factual causation, and, hence, legal causation where factual causation is required underlie what the judge wrote in Andrusko? If it does, that’s a mistake, too. But that’s a mistake repeated in para. 8 of Clements and existed before Clements. As ever, it’s the analytical (not real) problem of relevant multiple sufficient factual causes in a regime which claims that the but-for test is the definition of factual causation. In Andrusko, the trial judge found that the other factor(s) – here the pre-existing conditions: the other suggested independently (of the neligent act, so not part of the causal set of factors that includes the negligent act) sufficient cause – probably wouldn’t have caused the post accident complaints even if the negligent act hadn’t occurred. That means there was a relevant change of position.
Why did I write “relevant change of position”? Because the other causal candidate, if independently sufficient, of itself, was never actionable. There’d still have been no change in position if the other causal candidate was an actionable event. But then there could be legal responsibility notwithstanding the absence of change of position, because, in common law Canada (as a general rule) we don’t allow the defence of “somebody else’s actionable conduct is also a cause”, regardless of whether “also” means, “together” or “independently”.
The continued failure of too many judges, starting at the SCC, to clearly separate, and keep separate, the concepts of factual causation and scope of legal responsibility is a significant part of the explanation for the confusion in causation jurisprudence. But, then, I’ve said that, before, haven’t I? And, I’m not saying anything that’s new.
Addendum: The Snell statement “injuries … [which] may very well be due to factors unconnected to the defendant and not the fault of anyone” tells us why but-for factual causation isn’t enough for legal causation in a regime that requires some level of relevant causal connection between compensable injury and actionable fault of a wrongdoer. So, the mere fact I’m speeding through the intersection when blue ice falling from flying pigs strikes the passenger in a seat in my convertible doesn’t make my speed a but-for cause for legal purposes, even though the incident would not have occurred had a driven at the speed limit: even though, but-for the fact I was speeding, the vehicle wouldn’t have reached the intersection at the required time.
In addition, given the Snell panel’s position that there was no reason to depart from existing causation principle which were then seen to be adequate when properly applied, so that the SCC, on that basis, rejected what’s now understood to have been, in McGhee, a nascent statement of the material contribution to risk principle, we can see, in the statement “injuries … [which] may very well be due to factors unconnected to the defendant and not the fault of anyone”, room for the rationale for material contribution to risk (MC-R) as explained in Clements. In the MC-R scenario seemingly envisaged by Clements, the same evidence produces the conclusions that the injuries may be due to the actionable fault of a person, are necessarily due to the (at least once actionable) fault of another person: put more simply, “may very well be due to factors connected to the defendant, even if that can’t be established on the balance of probability, and are the fault of someone”.
“But for” Clements, these reasons might make sense. As I appear before Ontario judges, I should be cautious, but I think I can safely call myself mystified by the spin put on Clements. It has materially contributed to my confusion. The judge seems to take a routine situation of weighing evidence and over complicates it. All he or she had to say was “I am not satisfied that the injuries made the Plaintiff any worse” and pfootnote Clements so the Court of appeal knows it was considered…