The Latin phrase res ipsa loquitur means “the thing speaks for itself.” In tort law, res ipsa loquitur applies in cases where the court can assume someone acted negligently based on how the plaintiff’s injury occurred.
In most tort cases, the injured plaintiff must prove four things:
(1) that the defendant had a duty of care toward the plaintiff;
(2) that the defendant breached that duty, usually by acting negligently or carelessly;
(3) that the injury would not have happened but for the breach; and
(4) that the plaintiff suffered damages of some kind, such as physical injury or loss of property.
In a res ipsa loquitur situation, however, the court assumes that a duty of care exists and that the defendant breached it. Therefore, the plaintiff can skip over proving parts 1 and 2, and focus on proving that the defendant’s negligence caused his injury and that he suffered damages as a result.
Res ipsa loquitur does not apply to all tort cases or even to all personal injury cases. Rather, res ipsa loquitur appears only with the type of injuries that do not occur unless someone is negligent. For instance, in Byrne v. Boadle, the first tort case to use res ipsa loquitur, the plaintiff was injured when a barrel of flour fell out of a second-story warehouse window and hit him on the head. The court held that res ipsa loquitur applied because barrels do not fall out of windows unless somebody is being negligent with them.
Today, courts ask two questions when deciding if res ipsa loquitur applies to a case:
(1) Is this the kind of accident that would be caused by negligence?
(2) Did the defendant have exclusive control over whatever caused the accident?
If the answer to both questions is “yes,” the court may hold that res ipsa loquitur applies. If so, the parties do not have to argue over whether the defendant was negligent. Instead, they may focus on whether defendant’s negligence caused the plaintiff’s injury and how to measure the plaintiff’s damages.
Res ipsa loquitur may be applied in a wide range of tort cases. It commonly appears in medical malpractice cases, especially ones where a piece of medical equipment is accidentally left inside the patient during surgery. Equipment does not get left behind unless the operating team is not counting carefully, and the operating team has exclusive control over the surgical equipment, including whichever piece was left inside the patient.
Courts ask whether the defendant had exclusive control because res ipsa loquitur may not apply if the plaintiff’s own negligence caused his injury or made it worse. For instance, suppose a worker at a construction site negligently parks a wheelbarrow so that it blocks the whole sidewalk. A bicyclist runs into the wheelbarrow, which he didn’t see because he was sending a text message on his phone and not watching where he was going.
In this case, a court may apply either rule of contributory negligence or the rule of comparative negligence. In contributory negligence, if the plaintiff was negligent at all, he cannot win his case, even if the defendant was more negligent than the plaintiff. In comparative negligence, the plaintiff can win if his negligence is less than 50% responsible for his injuries, but his damages will be reduced by the percentage that he was negligent. Res ipsa loquitur does not apply in either contributory negligence or comparative negligence cases because the cause of the plaintiff’s injury was not in the defendant’s exclusive control. That is, the plaintiff controlled part of what caused his injury.
A defendant may argue that res ipsa loquitur does not apply because the event that caused the plaintiff’s injury was an inevitable occurrence that the defendant could not have prevented. An inevitable occurrence also defeats res ipsa loquitur because the defendant lacked control over what caused the injury.