Res ipsa loquitur: how an accident can prove negligence

Most negligence claims rest on proof of what the defendant did. Sometimes nobody knows. A barrel falls out of a warehouse window, a bottle explodes, a patient wakes from surgery with an injury far from the surgical site. Res ipsa loquitur is the doctrine that lets a plaintiff in that position ask the jury to infer negligence from the accident itself. Cornell's Wex encyclopedia describes it as a way to carry the burden of proof using what amounts to circumstantial evidence (Wex: res ipsa loquitur).

Where the doctrine comes from

The usual starting point is Byrne v. Boadle, an 1863 English case that Wex cites as an example of a court applying the doctrine. A barrel of flour fell from a warehouse window onto a man passing below. He could not say how the barrel came loose, but barrels do not ordinarily fall out of warehouses unless someone was careless, and the warehouse controlled the barrels. The same reasoning still frames the doctrine.

The three elements

Wex lists three things the plaintiff has to show:

1. The incident is of a type that does not generally happen without negligence.
2. It was caused by an instrumentality solely within the defendant's control.
3. The plaintiff did not contribute to the cause.

California's jury instruction states the same three elements in plain words (CACI No. 417). The cases collected with it explain what each element is for. The first establishes that someone was probably negligent. The second and third link that probability to this defendant and rule out the plaintiff as the cause.

What the first element needs

The plaintiff has to show the accident is the kind that usually means negligence. The California Supreme Court said in Zentz v. Coca Cola Bottling Co. of Fresno (1952), quoted with CACI No. 417, that this showing can rest on everyday experience or on the evidence at trial. A falling barrel speaks for itself to any juror. A complication after surgery may not. California's medical malpractice version, CACI No. 518, includes an optional sentence telling jurors to consider expert testimony on that question, and to rely only on it when the judge finds the issue is beyond common knowledge.

Control by the defendant

The control element is about responsibility, not physical possession at the moment of injury. The California Supreme Court explained in Newing v. Cheatham (1975), also quoted with CACI No. 417, that the point of the control requirement is to connect the defendant to the probability that the accident was negligently caused. A bottler can be in control of a bottle that explodes in a store if nothing happened to it after it left the bottler's hands.

Courts have stretched control in some settings. In Ybarra v. Spangard (1944), the California Supreme Court allowed an unconscious surgical patient who woke with a shoulder injury to rely on the doctrine against the doctors and nurses who had charge of him, even though he could not say which of them caused it.

The plaintiff's own role

The third element keeps the doctrine away from accidents the plaintiff may have caused. Wex notes that an injury that could not occur without some fault of the plaintiff, such as some slip-and-fall accidents, fails this element. California's cases add a qualification. The plaintiff does not have to have been entirely passive, as long as the evidence eliminates the plaintiff's conduct as a cause. And the element is not the same as comparative fault, which the defendant still has to prove.

Inference or presumption?

States differ on how much the doctrine does once the elements are shown. In some, such as Wisconsin, pattern instructions treat it as a permissive inference the jury may accept or reject (Wis. JI-Civil 356). California treats it as a presumption affecting the burden of producing evidence (Evid. Code § 646).

The California version works in steps. If the plaintiff proves the three elements and the defendant offers nothing in response, the jury must find negligence. If the defendant offers evidence that would support a finding of no negligence, or that its negligence did not cause the accident, the presumption drops out. The jury may still draw an inference of negligence from the facts, but it finds negligence only if, after weighing all the evidence, it is more probable than not. CACI No. 417 tells jurors that negligence is a finding they are permitted, though not required, to make. If the plaintiff fails to prove all three elements, the jury still decides negligence under the ordinary instructions.

Questions to test whether the doctrine fits

• Does this kind of accident usually mean someone was careless? Think about whether an expert would need to say so.
• Who controlled what caused it? Trace the object or procedure back to the defendant.
• Could anything you did have caused it? If so, the doctrine is harder to use.
• Is there direct evidence instead? Witnesses or records may prove negligence without the doctrine.
• Which state's law applies? The weight of the inference depends on the state.

This guide explains general legal concepts and is legal information, not legal advice. Consult a lawyer licensed in the relevant jurisdiction about a specific situation.