Also known as: but-for causal chain · but for causation chain · but-for test · but for test · causal chain
Written by attorneys · grounded in primary & secondary sources — see below
A sequence of events in which each antecedent is a necessary condition for the occurrence of the subsequent event and ultimately the harm. The but-for test asks whether the result would have occurred when and as it did in the absence of the defendant's conduct or omission.
Boreal Energy supplied a prescription drug to physicians after warning them of a known cardiac risk. Dr. Bernard Bass reviewed the warning, exercised independent judgment, and prescribed the drug to patient Bianca Blanco. Bianca suffered the cardiac event. The manufacturer is not liable because the physician's judgment broke the causal chain between the warning and the patient's injury.
Officers arrested suspect Sam Stone without probable cause or a warrant. After several hours, repeated Miranda warnings, and a visit from friends, Sam confessed. The confession must be excluded because the causal chain from the unlawful arrest was not broken by the passage of time or the warnings.
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Conduct is a factual cause when it is an antecedent but for which the result would not have occurred when and as it did. This test applies to both acts and legally relevant omissions where the actor has a duty to act.
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Yes. The rule recognizes that more than one antecedent can satisfy the but-for test, and either one may support liability when the other elements of the offense or claim are met.
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An independent, counseled decision made after sufficient time can sever the causal chain from an earlier illegality, rendering later evidence admissible under the attenuation doctrine.
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A physician's independent medical judgment in prescribing a drug breaks the causal chain between the manufacturer and the patient when the manufacturer has adequately warned the physician of the drug's risks.
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