if the B.C. Court of Appeal is prepared to listen to the views of the Ontario Court of Appeal on the meaning of Clements v. Clements, 2012 SCC 32, on this issue, assuming the Supreme Court of Canada doesn’t comment on this issue in its Ediger reasons (appeal argued December 4, 2012, judgment reserved), whenever they’re released. See Goodman v. Viljoen, 2012 ONCA 896 at paras. 70-76. The text of the paragraphs is quoted later in this posting.
(updated Jan 9/13: added CanLII citation and the last 2 sentences above)
The formally unique to BC rule in Moore v. Castlegar is that the Snell robust, pragmatic, commonsense, approach to the application of the but-for test isn’t available where expert evidence is adduced on causation. The latest iteration of that rule by the British Columbia Court of Appeal requires that both plaintiff and defendant adduce expert evidence. There are pronouncements in earlier BCCA cases which don’t require that both sides lead that evidence.
The BCCA wrote in Ediger v. Johnston, 2011 BCCA 253 at para. 84
 This court confirmed in Moore v. Castlegar& District Hospital (1998), 49 B.C.L.R. (3d) 100, [1998 CanLII 4906] (C.A.) that “where both parties have led expert evidence on the issues of causation, it is not open to this court to apply the ‘common sense’ reasoning urged in Snell”(para. 11).
I’m not aware of any case in which a judge commented on whether both sides lead expert evidence where only one side calls an expert witness but the other side cross-examines and then seeks to rely on that evidence.
In passing, that’s exactly what happened in Clements v. Clements, 2012 SCC 32.
The expert witness was called by the defence. The plaintiff sought to rely on what the plaintiff said the expert evidence meant. The trial judge held the plaintiff hadn`t satisfied the but-for test, on the evidence, but never suggested the Snell approach wouldn`t have been applicable in any event. When the SCC majority in Clements sent the case back for a new trial on the basis that the applicable test was the but-for test and the trial judge hadn’t applied it properly, the Court didn’t mention Moore v. Castlegar or Ediger.
While the Ediger panel was unanimous on that point, an earlier panel of the BCCA wasn’t, though Ediger didn’t mention that. Only a majority (2-1) approved the Moore rule in Sam v. Wilson (2007) BCCA 622. See para. 144 where the majority wrote: “Thus this Court held in Moore v. Castlegar … that it is not open to a trial judge to draw a common-sense inference of the cause of a medical condition where both parties have led expert medical evidence of causation.” However, Chiasson J.A., dissenting, thought differently about the meaning of Moore. He wrote, at paras. 40-42.
 Relying on Moore v. Castlegar & District Hospital (1998), 49 B.C.L.R. (3d) 100 (C.A.), Dr. Wilson asserts: “. . . where both parties have led expert evidence on the issues of causation, it is not open to this Court to apply the ‘common sense’ reasoning urged in Snell v. Farrell…”. I do not think the reasoning in Moore extends so far.
 In Moore the Court said in para. 11: “. . . in a case such as 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’”. Moore was an unusual case. The trial judge rejected the only evidence that supported the assertion the plaintiff had voluntary movement of his legs at the scene of the accident. The medical evidence was unequivocal that if the plaintiff did not have voluntary movement of his legs at the scene of the accident, his injury was sustained in the accident and was not caused by the conduct of hospital personnel. After commenting on Snell v. Farrell, Hollinrake J.A. stated in para. 11:
I take it this is what the trial judge was referring to when she said:
All parties have led evidence on this issue [causation] and it would be inappropriate to resort to an inferential analysis as was argued on the plaintiff’s behalf.
The Court also noted in para. 5 that after rejecting the evidence concerning voluntary movement, the trial judge said: “[w]ithout evidence of movement, the expert evidence is clearly to the effect that the plaintiff’s injury was sustained in the motor vehicle accident”.
 As McLachlin C.J.C. stated in para. 9 of Resurfice Corp.: “. . . a trial judge is not obliged to consider the opinions of expert witnesses if he can arrive at the necessary conclusions on issues of fact and responsibility without doing so”.
Chiasson J.A. seems to have said that Moore v. Castlegar should be understood to have said no more than that in a particular case, the judge or jury may conclude that the state of the expert evidence precludes resort to the Snell robust and pragmatic approach.
The status of the rule in Moore v. Castlegar is one of the issues that is formally before the SCC in the Ediger appeal but you’d not know that from the way the appeal was argued; nor did any of the questions from the bench imply that any member of the SCC thought that there’s merit to the rule. I’ve pointed out before (on this site and elsewhere) that there is post-Mooore SCC authority – serendipitously a decision on appeal from the BCCA where experts testified for both plaintiff and defendant – that makes the rule (as stated in Ediger) wrong. See K.L.B. v. British Columbia,  2 SCR 403 at para. 13, 2003 SCC 51 per McLachlin CJ (writing for a unanimous 9 member panel):
Before turning to this, however, it is worth noting that the private nature of the abuse may heighten the difficulty of proving the abuse and its connection to the government’s conduct in placement and supervision. As in other areas of negligence law, judges should assess causation using what Sopinka J., citing Lord Bridge in Wilsher v. Essex Area Health Authority,  2 W.L.R. 557 (H.L.), at p. 569, referred to as a “robust and pragmatic approach” (Snell v. Farrell,  2 S.C.R. 311, at p. 330). As Sopinka J. emphasized, “[c]ausation need not be determined [with] scientific precision” (Snell, at p. 328). A common sense approach sensitive to the realities of the situation suffices.
This point in K.R.B. seems to have been ignored or missed (even in B.C.)
In Goodman v. Viljoen, 2012 ONCA 896, Doherty J.A. (dissenting on other grounds – the majority probably agreed on this point but didn’t find it necessary to say so) wrote:
 Counsel for the appellant [defendant] submits that because the defence led evidence to contradict the plaintiffs’ causation evidence, the trial judge erred in taking a robust and pragmatic approach to the evidence of causation. That proposition finds some support in Ediger v. Johnston, 2011 BCCA 253, 333 D.L.R. (4th) 633, at paras. 83-85, leave to appeal to S.C.C. granted,  S.C.C.A. No. 371.
 The appellant’s contention does not, however, find support in the case law from the Supreme Court of Canada or this court: see Snell v. Farrell,  2 S.C.R. 311, at p. 330; Clements v. Clements, 2012 SCC 32, 346 D.L.R. (4th) 577, at para. 46;Fisher v. Atack, 2008 ONCA 759, 242 O.A.C. 164, at paras. 54-59, leave to appeal to S.C.C. refused,  S.C.C.A. No. 14; Aristorenas v. Comcare Health Services (2006), 83 O.R. (3d) 282 (C.A.), at paras. 54-61, leave to appeal to S.C.C. refused,  S.C.C.A. No. 487.
 In Snell, at p. 330, in the exact passage relied on by the appellant, Sopinka J. makes it clear that the robust and pragmatic approach to evidence of causation applies when the defence leads evidence to contradict the plaintiffs’ causation theory:
The legal or ultimate burden remains with the plaintiff, but in the absence of evidence to the contrary adduced by the defendant, an inference of causation may be drawn although positive or scientific proof of causation has not been adduced. If some evidence to the contrary is adduced by the defendant, the trial judge is entitled to take account of Lord Mansfield’s famous precept. This is, I believe, what Lord Bridge had in mind in Wilsher when he referred to a “robust and pragmatic approach to the … facts” (p. 569). [Emphasis added.]
 The first sentence of the above-quoted passage speaks to the drawing of an inference of causation in the absence of positive evidence of causation from the plaintiff, and the absence of any evidence from the defendant. The second sentence speaks to the approach to be taken to the evidence when there is conflicting evidence from the defence. Sopinka J. applies the “robust and pragmatic approach” to cases in which the defence has led evidence.
 Whatever controversy there may have been in the case law was put to rest in Clements. The Chief Justice, in the course of summarizing the present law of causation in Canada, stated, at para. 46:
As a general rule, a plaintiff cannot succeed unless she shows as a matter of fact that she would not have suffered the loss “but for” the negligent act or acts of the defendant. A trial judge is to take a robust and pragmatic approach to determining if a plaintiff has established that the defendant’s negligence caused her loss. Scientific proof of causation is not required.
 Nothing in the Chief Justice’s summary suggests that a different approach is to be taken to the evidence when the defence calls evidence relevant to causation.
 The robust and pragmatic approach describes the manner in which evidence is to be evaluated, not some special burden of proof: see Aristorenas, at para. 56. The robust and pragmatic approach takes into account the nature of the factual issues underlying the causation question and the kind of evidence that the parties are reasonably capable of producing on those issues. The approach acknowledges that the causation inquiry is essentially a practical one based on the entirety of the evidence and made with a view to determining whether the plaintiff has established causation on the balance of probabilities and not to a scientific certainty. Clearly, as counsel for the appellant urges, the robust and pragmatic approach does not countenance speculation or resort to common sense to determine issues that require expert knowledge. To resort to speculation or the misuse of common sense is to misapply the robust and pragmatic approach.
I suppose the reason the ONCA finally got around to commenting on the BCCA’s limitation on the use of the Snell commonsense approach – apart from the fact that it had to because the argument was made by the appellant – is that it had to be addressed now that the but-for test is (seemingly) the only test for the determination of the factual causation issue in negligence actions (at least). It could have been ducked in the 1996- 2007 era of the Athey material contribution to injury alternative – at least as that alternative was understood before Resurfice.
Or maybe not. Perhaps the reason is that a well-regard Ontario trial judge had recently suggested there might be some validity to the Moore v. Castlegar rule.