What is the test for quantifying damages in a personal injury action?

The overarching legal principle in quantifying damages is that, insofar as is possible, the plaintiff should be put in the position he would have been in but for the injuries caused by the defendant's negligence: Lines v. W & D Logging Co. Ltd., 2009 BCCA 106 at para. 185, leave to appeal ref'd [2009] SCCA No. 197. Compensation must be made for the loss of earning capacity as a capital asset and not merely the loss of earnings: Andrews v. Grand & Toy Alberta Ltd., 1978 CanLII 1 (SCC), [1978] 2 S.C.R. 229 at 251-254. Nevertheless, a pecuniary loss must be established, the existence of which is typically assessed by comparing what would have been the plaintiff's future earnings if the accident had not occurred with the plaintiff's likely future earnings given the accident did occur.

The determination of what would have happened in both the past and the future had it not been for the accident, and the determination of what will happen given the accident did occur, are hypothetical exercises. While actual past events must be proven on a balance of probabilities, the standard of proof in relation to hypothetical events is simple probability: Athey at para. 27. If a plaintiff establishes a real and substantial possibility, as opposed to a speculative possibility, of a hypothetical event, the event must be given weight according to its relative likelihood and compensation must be awarded based on an estimation of the chance that the event will occur: Steward v. Berezan, 2007 BCCA 150 at para. 17. The court must make allowances for the possibility that the assumptions upon which the determination is based may prove to be wrong, and all contingencies that are established as realistic as opposed to speculative possibilities must be given effect.