A test commonly used to determine Proximate cause also known as legal cause. Proximate cause is the primary cause of an injury. One of several tests to determine a defendant's responsibility for the subject of a lawsuit or criminal proceeding. For example, the prosecutor may need to argue that: "But for the defendant's speeding, the car would not have gone out of control, and therefore the defendant is responsible." This is shorthand for whether the action was the "proximate cause" of the damage.