Can a defendant be held to be 100% liable for a non-tortious cause of injury?

The concurrent existence of non-tortious causes of the injury will not relieve a defendant from liability. Full liability may attach if it can be shown that the defendant’s negligence was one of the sources that contributed to the harm. To allow otherwise would restrict full recovery to those cases where the defendant’s actions are the sole cause of the loss. This is against the established principles and purposes of tort law. Instead, a defendant may be held to be one hundred percent liable if it can be shown, as discussed above, that his/her actions were a material cause of the harm: Athey v. Leonati, 1996 CanLII 183 (SCC), [1996] 3 S.C.R. 458 at paras. 19-20.