Those of you in British Columbia who (need or ought to) care about such things may have noticed an almost boilerplate quality in the paragraphs in recent British Columbia Supreme Court decisions setting out the principles of factual causation in negligence. This, on the whole, is a good thing and the judges should be commended.
On the other hand, what’s not good is that the boilerplate is literally wrong. (It’s still safe for me to say these things since I don’t have to appear in front of British Columbia judges.) So far, though, that hasn’t seemed to affect the validity of the judges’ decisions.
A very recent example is Erickson v. Sibble, 2012 BCSC 1880. This is the boilerplate.
● General Principles
For Ms. Erickson to recover damages, there must be a causal link between the Accident and the injuries she has suffered. The law does not draw a distinction between injuries that are psychological or physical in nature. The primary test used in determining causation is known as the “but for” test. The plaintiff bears the burden of showing that “but for” the defendant’s negligent act or omission, her injury would not have occurred. Applying it here requires that Ms. Erickson prove that it is more likely than not likely that without the Accident her injuries would not have occurred: Athey v. Leonati,  3 S.C.R.; 458; Blackwater v. Plint,  2 S.C.R. 3.
 The causation test does not demand scientific precision and is not to be applied too rigidly: Snell v. Farrell,  2 S.C.R. 311. Causation is a practical question of fact which can best be answered by ordinary common sense.
 The plaintiff need not establish that a defendant’s wrongful conduct is the sole cause of her injury. So long as the plaintiff establishes a substantial connection between the injuries and the defendant’s negligence beyond the “de minimis” range, the defendant will be fully liable for the harm suffered by a plaintiff, even if other causal factors, which he is not responsible for, were at play in producing the harm: Farrant v. Laktin, 2011 BCCA 336; Athey; Resurfice Corp. v. Hanke, 2007 SCC 7; Clements v. Clements, 2012 SCC 32.
The problem in para. 220 is that it is incomplete and not accurate because it is set out as a statement of a general principle of causation as it relates to “damages”. However, there are additional “damages” principles that aren’t set out in para. 220. In order for the plaintiff to recover “damages” which result from “damage” – injury – which is caused by actionable negligence, the plaintiff must satisfy the separate damages principles, too. Perhaps that what why the trial judge referred to Blackwater, too. What is missing from para. 220 is the change from the “original position” requirement. This is in Athey in paras. 32 and 41.1
 … The essential purpose and most basic principle of tort law is that the plaintiff must be placed in the position he or she would have been in absent the defendant’s negligence (the “original position”). However, the plaintiff is not to be placed in a position better than his or her original one. It is therefore necessary not only to determine the plaintiff’s position after the tort but also to assess what the “original position” would have been. It is the difference between these positions, the “original position” and the“injured position”, which is the plaintiff’s loss. In the cases referred to above, the intervening event was unrelated to the tort and therefore affected the plaintiff’s “original position”. The net loss was therefore not as great as it might have otherwise seemed, so damages were reduced to reflect this.
[41.1] If the disc herniation would likely have occurred at the same time, without the injuries sustained in the accident, then causation is not proven.
Erickson is a thin skull (pre-existing injury) case.
The current problem with para. 221 is that while it is an accurate enough (for present purposes) statement of what the Supreme Court said in Snell, it is also incomplete as a statement of what the law is in British Columbia as to when the common sense approach can be used. As it stands, the law is as set out most recently in Ediger v. Johnston, 2011 BCCA 253 at para. 84:
 This court confirmed in Moore v. Castlegar& District Hospital 1998 CanLII 4906 (BC CA), (1998), 49 B.C.L.R. (3d) 100 (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).
Both sides called expert evidence in Erickson. However para. 221 is the only time the trial judge mentioned Snell or common sense, so perhaps the trial judge didn’t apply “common sense” reasoning, whatever that means, assuming that means something different from otherwise valid reasoning, in deciding whether to accept the plaintiff’s evidence (including expert evidence) rather than the defendants.
On the other hand, perhaps the trial judge concluded (but chose, out of discretion not to mention) that the SCC’s decision Clements necessarily, albeit implicitly, overrules the Ediger/Moore doctrine (since Clements is a decision on appeal from the BCCA) as Clements repeats the Snell proposition about common sense without making the Ediger/Moore qualification for cases having expert evidence. Clements states
 The “but for” causation test must be applied in a robust common sense fashion. … A common sense inference of “but for” causation from proof of negligence usually flows without difficulty. Evidence connecting the breach of duty to the injury suffered may permit the judge, depending on the circumstances, to infer that the defendant’s negligence probably caused the loss. See Snell and Athey v. Leonati, 1996 CanLII 183 (SCC),  3 S.C.R. 458. … Where “but for” causation is established by inference only, it is open to the defendant to argue or call evidence that the accident would have happened without the defendant’s negligence, i.e. that the negligence was not a necessary cause of the injury, which was, in any event, inevitable. …… 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. …… The foregoing discussion leads me to the following conclusions as to the present state of the law in Canada:
(1) 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…
There are a number of problems with para. 222 as written. I’ll mention two.
The first is the “de minimis” bit. It’s an accurate statement of what the BCCA has said British Columbia law is. It is, generally, an accurate statement of causation jurisprudence once one brings in remoteness law and damages law. However, it is not an accurate statement of factual causation jurisprudence. Once again, there’s Athey, at para. 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.
[Emphasis in Athey.]
So, if there is a de minimis limitation on necessary causes which makes them not actionable factual causes, even if they are necessary causes, it comes from somewhere not mentioned in Erickson because remoteness wasn’t an issue in Erickson. (It might be implicit in Athey, 41.3, but that’s another problem we won’t get into here. See Nattrass v Webber 2010 ABCA 64 at para. 47 – “In Athey, deminimis or “non‑material contribution” is an exception to liability where several causes contribute to the damage. It could be described as a type of de minimis defence or limit on liability.” – if you’re interested. )
In any event, para. 222 doesn’t seem to be about remoteness or damages assessment.
The second problem I’ll mention is that para. 222 was probably meant to refer to instances where the various causal factors, even those for which the defendant “is not responsible” are cumulatively necessary to make up the cause of the injury. Limited in that fashion, the paragraph is a correct statement of the law. However, what does “other causal factors, which [the defendant] is not responsible for, were at play in producing the harm” literally mean. As written, it covers even those instances where the “other causal factors” are capable of being but-for causes even if the defendant’s negligence had not occurred, whether the other causal factors are all tortious or all “innocent”.
If there was a never actionable (i.e., innocent) causal event – other than the injured person’s own contributory fault – which would have been a but-for cause of the injury even if the negligence had not occurred, then the damages are not actionable. This problem is connected to the problem in para. 220. I’ve set out the paras. from Athey, above.
If, however, the other events capable of also being but-for causes were actionable, then they do not provide the sued defendant with a defence: see Blackwater v. Plint and a host of other cases. That’s also explicit in Clements, at para. 12 – which I omitted, above, intentionally, even if (I think) not phrased as clearly as it ought to have been (for those not paying close enough attention). It is:
 In some cases, an injury — the loss for which the plaintiff claims compensation — may flow from a number of different negligent acts committed by different actors, each of which is a necessary or“but for” cause of the injury. In such cases, the defendants are said to be jointly and severally liable. The judge or jury then apportions liability according to the degree of fault of each defendant pursuant to contributory negligence legislation
That paragraph has to be understood as meaning the situation where the evidence is enough to show that each of the different acts referred to would be a but-for cause even if all of the other negligent acts had not occurred. Otherwise, it becomes a statement of the scenario to which the material contribution to risk test summarized in para. 46(2) Clements applies, but the premise of that situation is that the evidence is NOT enough to allow the court to validly identify any one of the multiple negligent causes is a but-for cause, or to say that any two or more or all of them cumulatively combine, where the premise also is that those causal candidates are the only relevant candidates.