Unascertainable cause is when there are multiple potential actions that resulted in an injury, but it is unclear which act actually caused the injury.
Unascertainable cause in tort law means that multiple defendants are simultaneously negligent, but only one injury results. Therefore, it is uncertain which defendant’s actions caused the plaintiff's injury and thus, which defendant should be held liable. In this case, the burden of proof shifts from the plaintiff or prosecutor, to each defendant who must provide evidence to prove that their breach of duty did not cause the plaintiff's injury. If neither defendant can satisfy this burden of proof, then both defendants can be held joint and severally liable, that is, each defendant is individually liable for the injury.
An example of a case with unascertainable cause is if two defendants each shoot their victim at the same time, with the same type of gun, standing in the same location, and their victim dies; then the death was unascertainably caused because it’s unclear which defendant’s bullet resulted in the victim’s death.
[Last updated in June of 2024 by the Wex Definitions Team]
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