Indivisibility is …
a meaningless label or an admission that the judge or jury was unable to decide what the evidence means so opted to blame all of the defendants so that the plaintiff could recoup from the defendant(s) with assets.
Divisible injuries are those capable of being separated out and having their damages assessed independently. Indivisible injuries are those that cannot be separated or have liability attributed to the constituent causes.
Bradley v. Groves, 2010 BCCA 361 at para. 20.
What follows is why the label is meaningless or an instance of sticking one’s hand into a wrongdoer’s pocket.
Recall the explanation of the meaning of and justification for Canadian negligence law’s version of the concept of causation in Snell v. Farrell,  2 SCR 311, 1990 CanLII 70: ” Causation is an expression of the relationship that must be found to exist between the tortious act of the wrongdoer and the injury to the victim in order to justify compensation of the latter out of the pocket of the former.”
Assume a case where the evidence shows that there are a number of events (conditions) other than the defendant’s negligence which occurred, prior to the trial. Assume, too, that on the evidence all of these other events could be causes of the injury the plaintiff alleges was caused by the negligence of a defendant. Where there are multiple conditions amounting to negligent, we have multiple wrongdoers, not just one wrongdoer who has committed multiple negligent acts.
All of the other conditions are events which were wrongful and could have been actionable.
The only reason that it matters whether the court (judge or jury) is able to divide the injury (and the damages) between the multiple wrongdoers is that the plaintiff may not have sued the wrongdoer(s) with assets, or has sued the “wrong” wrongdoer in the sense that the significant portion of the injuries would be found to have been caused by a wrongdoer who is not sued, or does not have assets. If the injury and damages are divisible, there isn’t joint liability.
At least one of the other condition was an event which was never actionable, even if it is wrongful.
In this variation, the problem for the plaintiff is that if the evidence shows that each of the negligence AND any of the non-actionable conditions were independently sufficient causes of the plaintiff’s injury, then the plaintiff’s action fails. This is not a factual causation but a legal causation, or a damages assessment, issue. See Athey v. Leonati,  3 SCR 458, 1996 CanLII 183, at paras. 31-2, 41.1.
So, by finding that the evidence is such that the injuries (and damages) are indivisible consequences of all of the causal conditions, including the never actionable conditions, the court treats the injuries (and damages) as if there was finding that the negligence and the non-actionable conditions were cumulatively necessary causes of the injuries (and damages). Any defendant found to have caused the injury (and damages) on this basis is jointly liable for all of the compensable damages (assuming there is no applicable law that limits that defendant’s extent of liability). It doesn’t matter, then, that the plaintiff did not sue all of the persons whose conduct was an actionable cause, so long as the defendant(s) sued have sufficient assets.
The injured person’ seatbelt contributory fault in motor vehicle accidents is a policy aberration. That contributory fault is, obviously, an event which is not actionable by the injured person. However, a policy decision has been made, by judges, that the plaintiff will still recover something even in cases where, had the plaintiff used the restraint properly, the injury probably would not have occurred. That result, on its face, is inconsistent with Athey v. Leonati. The factual distinction between contributory fault of the injured person that was a cause of how the event which resulted in the injury occurred and improper (or no) seatbelt use is said to be that contributory fault of the plaintiff in the manner of using seatbelts relates only to the manner in which the injury occurred. This is a meaningless distinction for the question: what were the causes of the injury.
All of the causal candidates are negligent causes. All are or were actionable. The court is unable to decide, on the evidence and on the balance of probability, whether any one of the causal candidates, or any combination of them fewer than all of them, is a sufficient to have caused the injury. However, the court is satisfied, on the evidence, that there is no probable cause other than one or more of the negligent causes.
This is scenario described in para. 46 (2) of Clements as the requirement for the material contribution to risk doctrine to be capable of applying at all.
(2) Exceptionally, a plaintiff may succeed by showing that the defendant’s conduct materially contributed to risk of the plaintiff’s injury, where (a) the plaintiff has established that her loss would not have occurred “but for” the negligence of two or more tortfeasors, each possibly in fact responsible for the loss; and (b) the plaintiff, through no fault of her own, is unable to show that any one of the possible tortfeasors in fact was the necessary or “but for” cause of her injury, because each can point to one another as the possible “but for” cause of the injury, defeating a finding of causation on a balance of probabilities against anyone.
Clements v. Clements, 2012 SCC 32.
Since, at the moment, liability resulting from the application of the Clements material contribution to risk doctrine is joint (except perhaps in British Columbia – and maybe Nova Scotia – since under these provinces contributory fault statutes the effect of a plaintiff’s contributory fault is to make a defendant liable proportionally, only) what is the difference in result between the application of the indivisible injuries doctrine and the Clements material to risk doctrine?
Or, at least where the case is tried by a judge alone – so the judge understands what the law means – why should the judge make the findings of fact required to trigger Clements material contribution where it would be so much easier (and arguably far less validly reviewable on appeal – think of the palpable and overriding error requirement) for the judge to decide that the state of the evidence is such the injuries are indivisible.
At least one of the causal candidates was never actionable, even if wrongful. The court is unable to decide, on the evidence and on the balance of probability, whether any one of the causal candidates, or any combination of them fewer than all of them, is a sufficient to have caused the injury. However, the court is satisfied, on the evidence, that there is no probable cause other than one or more of the negligent causes.
The judge or jury has to decide that the injury (and damages) are indivisible for the plaintiff to succeed. If the judge or jury decides that any of the never-actionable conditions are an independently sufficient cause, the plaintiff must fail so long as the test for causation is the but-for test. See Athey, para. 41.1 and Clements, para. 46(1). If the not-actionable condition is separately sufficient, then it cannot be said that the negligence was necessary.
There is nothing in Clements that suggests Clements material contribution could apply to this situation (except perhaps in class actions – see para. 44 of Clements referred to in the “Negligence in the Air” will do posting that precedes this post). Clements as written implies that the material contribution to risk doctrine is not applicable where there is a never-actionable causal candidate. The plaintiff is unable to say that, for law, there can be no causes other than the negligence of one, or more, of the wrongdoers.