What is the test for establishing causation between a motor vehicle accident and a subsequent accident?

The plaintiff must prove on a balance of probabilities that his injuries would not have occurred “but for” the 2012 accident: Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458 at para. 14. The second accident does not need to be the only cause of the plaintiff’s injuries but it must be a causal factor beyond the “de minimis” range: Athey at para. 15. I find that causation is established. The question is to what extent his present problems are attributable to the 2012 accident.

The defendant is only liable for the injuries caused by the accident: Athey at para. 24. The defendant need not put the plaintiff in a better position than he was in prior to the accident: Athey at para. 35. Consistent with this principle, if “there is a measurable risk that the pre-existing condition would have detrimentally affected the plaintiff in the future, regardless of the defendant’s negligence, then this can be taken into account in reducing the overall award”: Athey at para. 35; see also Moore v. Kyba, 2012 BCCA 361 at para. 43.