The Law of Causation in Personal Injury Cases

In personal injury law, the plaintiff (the person claiming to be injured) must prove on a balance of probabilities that:

• The Defendant (the person or entity alleged to have caused the injury) owned the plaintiff a duty of care in law;
• The defendant breached the prescribed standard of care; and,
• Such breach caused the plaintiff’s damages.

Typically causation is determined on the basis of is what is referred to as the “ but for” test: if the plaintiff proves on a balance of probabilities that but for the defendant’s breach the loss would not have occurred, then the causation element has been met.

However in some situations this test has raised concerns that it sets the bar for liability too low or too high. For example in some cases it may be impossible for a plaintiff to satisfy the test in circumstances where it is clear that some defendant’s wrong has caused the loss, but not which defendant. There are other cases where the probability that a defendant’s wrong has caused the loss is less than would be required to satisfy the test. There are also cases where a wrongdoer’s acts are sufficient to have caused the loss but not necessary and therefore the “but for” test cannot be satisfied.

Important cases for Causation in Personal Injury Cases

• Resurfice v. Hanke [2007] 1 S.C.R. 333
• Snell v. Farrell, [1990] 2 S.C.R. 311
• Athey v. Leonetti [1996] 3 S.C.R. 458
• Cook v. Lewis, [1951[ S.C.R. 830
• Frazer v. Haukioja [2008] W.D.F.L. 2259
• Clements (Litigation Guardian of) v. Clements [2009] B.C.W.L.D. 5641