Once the plaintiff has shown that the defendant behaved negligently, he must then show that this behavior “caused” the injury complained of. Actually, P must make two quite distinct showings of causation:
Cause in fact: P must first show that D’s conduct was the “cause in fact” of the injury. This usually means that P must show that “but for” D’s negligent act, the injury would not have occurred.
Proximate cause: P must also show that the injury is sufficiently closely related to D’s conduct that liability should attach. This requirement is commonly called the requirement of “proximate cause” or “legal cause.”
Foreseeability: The requirement of “proximate cause” usually means that the injury must have been at least a reasonably foreseeable (and not bizarre or extraordinary) result of the defendant’s negligence.