What is the test for determining whether a defendant is liable for loss of income as a result of their actions?

The judge was live to the distinction between causation and damages, quoting from Blackwater v. Plint, 2005 SCC 58: 78. It is important to distinguish between causation as the source of the loss and the rules of damage assessment in tort. The rules of causation consider generally whether “but for” the defendant’s acts, the plaintiff’s damages would have been incurred on a balance of probabilities. Even though there may be several tortious and non-tortious causes of injury, so long as the defendant’s act is a cause of the plaintiff’s damage, the defendant is fully liable for that damage. The rules of damages then consider what the original position of the plaintiff would have been. The governing principle is that the defendant need not put the plaintiff in a better position than his original position and should not compensate the plaintiff for any damages he would have suffered anyway: Athey.

The first question is whether the tortfeasor caused or contributed to an injury, thus making him liable. Whether injuries are divisible or indivisible is relevant to whether liability is owed jointly. Where an injury is divisible, the torfeasor is only liable for that part of the injury which he caused: Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 SCR 458, at para. 24.

Divisible injuries are those that can be separated so that their damages can be assessed independently: Bradley v. Groves, 2010 BCCA 361, at para. 20.