Legal Definitions - but for rule

The but for rule is a fundamental test used in law to determine if a particular action or inaction was a necessary cause of an injury or harm. It asks whether the harm would have occurred "but for" the defendant's conduct. If the answer is no—meaning the harm would not have happened without that conduct—then the conduct is considered a "but for" cause of the harm.

This rule helps establish a basic factual link between someone's actions and an undesirable outcome, serving as a preliminary step in determining legal responsibility.

Examples:

• Workplace Safety Violation: An employer fails to properly maintain a piece of machinery, despite knowing it was faulty. An employee subsequently uses the machine, and due to the defect, suffers a severe injury.

  Explanation: Applying the "but for" rule, we ask: "But for the employer's failure to maintain the faulty machinery, would the employee have been injured in the same way?" If the evidence shows that the injury was directly caused by the defect that should have been fixed, then the employer's negligence is considered a "but for" cause of the employee's injury.

• Medical Malpractice: A doctor fails to order a standard diagnostic test for a patient presenting with symptoms indicative of a serious but treatable condition. As a result, the condition goes undiagnosed for several months, leading to a significant worsening of the patient's health that could have been avoided with earlier treatment.

  Explanation: Here, the "but for" rule would consider: "But for the doctor's failure to order the diagnostic test, would the patient's condition have deteriorated to the same extent?" If the test would have led to an earlier diagnosis and effective treatment, then the doctor's omission is a "but for" cause of the patient's worsened health.

• Property Damage from Negligence: A homeowner leaves a garden hose running overnight, causing a large volume of water to overflow their property and flood their neighbor's basement, damaging furniture and electronics.

  Explanation: Using the "but for" rule, we ask: "But for the homeowner leaving the garden hose running overnight, would the neighbor's basement have flooded and their property been damaged?" If the flooding was a direct consequence of the overflowing water, then the homeowner's action is a "but for" cause of the neighbor's property damage.