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.