Causation and Epidemiology
Causation Framework
The but-for test establishes cause in fact by asking whether the injury would have happened without the defendant's act or omission. If the harm would have occurred regardless, the conduct is not a cause in fact.
It fails where multiple sufficient causes exist.
Alternative Names:
But For Test, Sine Qua Non
Why it Matters?
The test's failure with multiple sufficient causes is why substantial factor analysis developed, since two independently sufficient causes each fail but-for while together they clearly caused the harm. In toxic tort and multi-defendant contexts that failure mode is common. The test remains the default elsewhere, and framing causation as a but-for question is generally favorable to defendants because it requires a counterfactual the plaintiff must prove.
Frequently Confused with
Related terms
Frequently asked questions
When does the but-for test fail?
Why do defendants prefer it?
