What is the "necessary cause" element in a motor vehicle accident inquiry?

At para. 41 of Athey, the requisite determination is summarized as whether it was necessary to have the accident for the post-accident health issues to occur. If so, then causation is proven, since the post accident health issues would not have occurred but for the accident. Even if the accident played a minor role, the defendant is fully liable because the accident was still a necessary contributing cause. The necessary cause element of the inquiry is key: Ediger v. Johnston, 2013 SCC 18.

There must be a substantial connection between the injury and the defendant’s conduct, however the defendant’s negligence need not be the sole cause of the injury, provided the plaintiff proves the accident was a cause of the injuries beyond the de minimus range: Athey, at paras. 17-20; Farrant v. Laktin, 2011 BCCA 336 at para. 9.