Torts
But-For Test
Definition
The but-for test is the foundational test for actual causation in tort law. It asks: but for the defendant's negligent act or omission, would the plaintiff's injury have occurred? If the injury would have happened regardless of the defendant's conduct, the defendant's negligence is not an actual cause. The but-for test can be difficult to apply in cases of concurrent causation or when multiple defendants are involved, prompting courts to use alternative tests such as the substantial factor test.
Example
A factory pollutes a river, and fish die downstream. If the fish would have died anyway from a separate natural cause, the factory's pollution fails the but-for test.