What is the test for establishing a probable cause in a personal injury case?

Whether one of a number of possible causes is a probable cause in any case cannot be considered in isolation and without regard to the relative strengths and weaknesses of the other possible causes. It is, I believe, open to a court at a trial in any such case to find that evidence is insufficient to establish that any one cause is more probable than the others - that the probable cause is undetermined or "accidental" - and, on that ground, that a plaintiff had not discharged the burden of proving causation. Such a decision was reached at trial in Cromie v. Fry, [1999] O. J. No. 4046 (S.C.J.) where Reilly J. stated: The task of establishing the origin and cause of fires may fairly be said to hold a special place in the law relating to negligence. That is because the best evidence as to origin and cause is so often destroyed or rendered less reliable by the fire itself. "Possible" causes may not be established as "probable" causes simply because the evidence has been destroyed. The court must carefully examine the available evidence and do its best to determine whether such evidence permits an inference, on a balance of probabilities, as to the cause of the fire. As in every case, mere speculation and conjecture are impermissible, absent an evidentiary base. However the court must be mindful of the unenviable position of the defendant, who may be left in the position, as a result of the fire, of being unable to demonstrate other probable causes of the fire. The court should not "seize upon" a remaining "possible" cause as the "probable" cause simply because the evidence of other "possible" causes has been destroyed.