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Res Ipsa Loquitur

The doctrine that lets an injured person prove negligence from the accident itself when the cause is unknown but the event is one that does not ordinarily happen without carelessness - its elements, the exclusive-control requirement and how it has loosened, what the doctrine does procedurally (an inference, or a presumption shifting the burden), and where it is and is not used.

Informational only - this is not legal advice. These definitions explain general legal vocabulary in plain English. They are not advice about your situation, reading them creates no attorney-client relationship, and the law differs from state to state and changes over time. For advice you can rely on, speak to a lawyer licensed in your state.

What it means

A negligence plaintiff must prove what the defendant did wrong. Sometimes that is impossible even though the accident plainly resulted from carelessness - a surgical instrument left inside a patient, a barrel falling from a warehouse window, an elevator dropping, a bottle exploding on a shelf, a bus leaving the road on a clear day. Res ipsa loquitur ("the thing speaks for itself") is the rule of circumstantial evidence that allows a fact-finder to infer negligence from the character of the accident when the plaintiff can show three things: that the event is of a kind that ordinarily does not occur without someone's negligence; that it was caused by an agency or instrumentality within the defendant's exclusive control (or, in the modern formulation, that other responsible causes, including the plaintiff's own conduct, are sufficiently eliminated); and that the plaintiff did not contribute to the harm. The plaintiff need not identify the specific act; the doctrine supplies the missing proof.

The exclusive-control element is applied with common sense rather than literally: a hotel is responsible for a chair thrown from an upper window only if the evidence points to the hotel rather than to a guest, while a manufacturer can be reached for a sealed product that failed even though it passed through a distributor and a retailer, because the evidence shows nothing happened to it along the way. Courts have relaxed the element further in medical cases where an unconscious patient is injured in a way unrelated to the procedure and several providers had control at different moments; in that situation some states let the inference run against all of them and require each to explain, since the patient cannot. Expert testimony is usually needed to establish the first element where the subject is technical - that a particular surgical outcome does not happen without negligence - but not where common experience supplies the answer.

What the doctrine does procedurally varies by state and is the point most often litigated. In most states it creates a permissible inference: the case goes to the jury, which may find negligence from the circumstances but need not, and the defendant may rebut with evidence of due care or of another cause. In some states it creates a presumption that shifts to the defendant the burden of producing evidence, or even of persuading the jury, that it was not negligent. The doctrine does not apply where the plaintiff has direct evidence of the specific negligent act (though the two can be pleaded in the alternative), where the accident is one that commonly occurs without fault, or where the cause is as consistent with an innocent explanation as with a negligent one. In strict-liability product cases the parallel "malfunction theory" lets a plaintiff prove a defect from the failure of a product in normal use without identifying the defect, and several states recognise a comparable inference for aviation and common-carrier accidents.

Where this comes from

Res ipsa loquitur is state common law, restated in Restatement (Second) of Torts § 328D and Restatement (Third) of Torts: Liability for Physical and Emotional Harm § 17 (2010). The doctrine originates in Byrne v. Boadle, 159 Eng. Rep. 299 (Exch. 1863) (the falling barrel), and the multiple-defendant medical application in Ybarra v. Spangard, 25 Cal. 2d 486 (1944); the classic American statements include Escola v. Coca Cola Bottling Co., 24 Cal. 2d 453 (1944) (the exploding bottle), and Larson v. St. Francis Hotel, 83 Cal. App. 2d 210 (1948) (the thrown chair, where the doctrine did not apply). Its procedural effect is codified in some states - California Evidence Code § 646 makes it a presumption affecting the burden of producing evidence - and is a matter of decision in the rest. The product-liability malfunction theory is Restatement (Third) of Torts: Products Liability § 3 (1998).

When people hire a lawyer for this

The doctrine is a tool for the case where the injury is obvious and the mechanism is not - a retained surgical object, a collapsing structure, an object falling from a building, a product that failed in normal use - and a lawyer should be asked whether it applies before the client assumes that not knowing what went wrong means having no case. It rarely wins on its own; the defendant will offer an innocent explanation, and the plaintiff's lawyer has to eliminate the other causes with evidence. Preserving the instrumentality - the product, the equipment, the records - immediately after the accident is what makes the doctrine usable later.

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Part of the LawyerLand plain-English legal glossary. Definitions are written from primary sources - statutes and court rules - and each entry states the authority it rests on, or says plainly when the doctrine is state law with no national rule.

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