Legal Definitions - but-for cause

But-for cause, also known as actual cause, is a fundamental legal concept used to determine if a particular action or omission directly led to a specific outcome or harm. It establishes a factual link by asking: "Would the harm or event have occurred but for the defendant's action or inaction?" If the answer is no—meaning the harm would not have happened without that specific action—then that action is considered a but-for cause of the harm.

This concept serves as a crucial first step in proving causation in both civil lawsuits (where someone seeks compensation for harm) and criminal prosecutions (where the state seeks to punish an offense). While it establishes the initial factual link, in many legal contexts, especially civil cases, it must be combined with other causation principles, such as proximate cause, to fully establish legal responsibility.

Here are some examples illustrating but-for cause:

• Civil Case (Negligence/Tort): A driver is speeding well above the limit and collides with another vehicle, causing significant damage and injuries to the other driver.

  • How it illustrates but-for cause: To determine if the speeding was a but-for cause of the accident, one would ask: "Would the collision and injuries have occurred but for the driver speeding?" If evidence shows that the accident would likely have been avoided or significantly less severe had the driver been traveling at a safe speed, then the speeding is considered a but-for cause of the harm.

• Civil Case (Breach of Contract): A construction company is hired to build a new office building by a specific deadline. Due to the company's failure to order essential materials on time, the project is delayed by several months, causing the client to lose rental income.

  • How it illustrates but-for cause: The question here is: "Would the client have lost rental income but for the construction company's failure to order materials on time?" If the delay in ordering materials directly led to the project's postponement and, consequently, the loss of rental income, then the company's inaction is a but-for cause of the financial loss.

• Criminal Case (Assault): During an argument, an individual shoves another person, causing them to fall backward and hit their head, resulting in a concussion.

  • How it illustrates but-for cause: To establish but-for cause, one would ask: "Would the victim have suffered a concussion but for the individual's shove?" If the act of shoving directly led to the fall and subsequent head injury, then the shove is a but-for cause of the concussion.