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Causation and Intervening Injuries

In the recent British Columbia Court of Appeal case Dunbar v Mendez (2016 BCCA 211), the defendant appealed the trial decision on a number of bases.  One of those was the alleged error of the trial judge in finding that an intervening back injury suffered by the plaintiff was caused by the crash.

In July of 2011, the plaintiff was injured in a serious motor vehicle crash, and suffered ongoing back problems as a result.  At some point after the crash, the plaintiff suffered a disc herniation when he pulled some wood.  This back herniation caused a loss of income for some period, and it eventually totally resolved.  The trial judge found the herniation (and therefore loss of income) to be caused by the crash, noting medical evidence that the plaintiff’s crash injuries had contributed to the herniation.  That contribution was legally sufficient to establish causation.  The Court of Appeal dismissed the defendant’s argument that the trial judge failed to apply the ‘but for’ test of causation correctly:

[56]         A judge is presumed to know the law and after having stated the law correctly, I see no reason to assume that she forgot it when making her finding of fact. I see nothing in the reasons to suggest that the trial judge failed to apply a “but for” test of causation premised on the principle that causation is established where one event is necessary (but not necessarily sufficient) to bring about another.

[57]         The appellants, in their reply factum, suggest that causation is not established “if a plaintiff does not prove that a defendant’s negligence was more than one of two or more independently sufficient causes”. The appellants do not provide any authority for that assertion, and I do not understand it to accurately state the law.  Rather, a defendant’s negligence on the “but for” test must be a necessary cause, but it need not, and generally will not be, a sufficient one. As the Supreme Court of Canada stated in Clements v. Clements, 2012 SCC 32:

[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.

[9]        The “but for” causation test must be applied in a robust common sense fashion. …

[11]      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. …

[12]      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. …

[58]         Here I am satisfied that the judge’s finding was that the motor vehicle accident was a necessary cause (and contributing in that sense) to the disc herniation. I would not accede to this ground of appeal.