What is the legal test for determining legal causation in a motor vehicle accident?

In the landmark case of Snell v. Farrell, 1990 CanLII 70 (SCC), [1990] 2 S.C.R. 311, Mr. Justice Sopinka addressed the perceived rigidity in the traditional judicial approach to causation. He memorably observed that in law it is not necessary to establish the causal connection with “scientific precision”. A determination of legal causation based on a weighing of the totality of available evidence will not be hampered by the absence of additional diagnostic testing. The accepted evidence will either be sufficient to prove causation on the balance of probabilities, or it will not.