How have courts considered causation in negligence actions?

In Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458 the court considered the issue of causation in negligence actions. In that case, the plaintiff suffered from a pre-existing disposition to back problems before he was involved in two motor vehicle accidents. He subsequently suffered a herniated disc during a warming up exercise. The herniation was caused by a combination of the plaintiff’s pre-existing condition and of the motor vehicle accidents. At paragraph 12, the court found that “it has long been established that a defendant is liable for any injuries caused or contributed to by his or her negligence. If the defendant’s conduct is found to be a cause of the injury, the presence of other non-tortious contributing causes does not reduce the extent of the defendant’s liability.”