A finding that a defendant’s conduct has fallen below the requisite standard of care does not necessarily make that defendant liable for the plaintiff’s injury. The plaintiff must also prove that the defendant’s substandard conduct caused the injury in respect of which the plaintiff is seeking damages.
 The primary test used in determining causation in negligence is the “but for” test. The plaintiff bears the onus of proving, on a balance of probabilities, that “but for” the defendant’s negligent act or omission, the injury would not have occurred: Athey v. Leonati,  3 S.C.R.; 458 [Athey]; Blackwater v. Plint, 2005 SCC 58 (CanLII), 2005 SCC 58; Clements v. Clements, 2012 SCC 32 [Clements]; Ediger (Guardian ad litem of) v. Johnston, 2013 SCC 18 (CanLII), 2013 SCC 18 [Ediger]. Inherent in the test is the requirement that the injury would not have happened without the defendant’s negligence: Clements at para. 8; Ediger at para. 28.
 The plaintiff need not establish that a defendant’s wrongful conduct is the sole cause of his injury. So long as a substantial connection between the harm and the defendant’s negligence beyond the “de minimus” range is established, the defendant will be fully liable for the harm suffered by a plaintiff, even if other causal factors, which the defendants are not responsible for, were at play in producing that harm: Farrant v. Laktin, 2011 BCCA 336; Athey; Resurfice Corp. v. Hanke, 2007 SCC 7 (CanLII), 2007 SCC 7 [Resurfice].
Chen v. Ross, 2014 BCSC 374
The answers are on the next screen. Don’t peek.
The propositions in paragraph 291 are about liability for compensable damages found to have been caused by actionable negligence. They are about limitations on the extent of liability. They are not about the prior question of whether the negligence was a factual cause of the damages.
In addition, para. 291 is correct for Canadian common law (as it now is) only if it is limited to two scenarios, except in British Columbia and arguably Nova Scotia where there’s a third. The first two scenarios:
1. the “defendant’s wrongful conduct” is a necessary part of a set of events which is, for the applicable law’s purposes, the ONLY sufficient cause of the damages;
2. if there is more than 1 such set of events, all of the sets are actionable. That’s because, as a matter of policy, Canadian common law doesn’t permit a tortfeasor, who could be held liable, to escape liability on the basis that somebody else’s actionable conduct is (or was) also a sufficient cause.**
3. the third scenario has the injured person also at fault for.
a. In all of Canada, where the injured person is also at fault, it is now generally the case that, where the plaintiff is also at fault for the plaintiff’s damages, the amount the plaintiff is entitled to recover will be reduced in some manner based on that fault. So, for that reason alone – there are others – it is not correct to assert ” So long as a substantial connection between the harm and the defendant’s negligence beyond the “de minimus” range is established, the defendant will be fully liable for the harm suffered by a plaintiff, even if other causal factors, which the defendants are not responsible for, were at play in producing that harm” without clarifying what one means by “fully liable”.
b. In British Columbia, at least, where the BC Negligence Act applies and the compensable injuries are found to have been caused by two or more wrongdoers, the plaintiff’s recovery from each of the wrongdoers held liable is limited to the portion of the compensable damages that corresponds to that wrongdoer’s degree of fault: “the liability to make good the damage or loss is in proportion to the degree to which each person was at fault”. The current label for that sort of limitation on the extent of liability is “several liability”.
**If you read the relevant paragraphs of the SCC’s reasons in Blackwater v Plint, carefully, particularly para. 82 – it’s the last sentence – you’ll realize that what the Court literally, explicitly, wrote and states is that a tortfeasor CAN escape liability if the other sufficient tortious conduct was once actionable but no longer is because of an expired limitation period. I doubt that’s what the Court intended. It’s inconsistent with the long-standing principle: you know, the one that says (generally) that in joint and several liability regimes it’s no defence if somebody else is also at fault.It’s inconsistent with Athey, It really wouldn’t matter whether the other torts were “statute-barred wrongs” if the conduct amount to those torts wasn’t also a cause of the conduct amounting to the actionable torts. But, then, I’ve doubted many things about aspects of the SCC’s statements about causation issues. Some of us know what and where that’s got me.