Res ipsa loquitur

In the common law of torts, res ipsa loquitur (Latin for "the thing speaks for itself") is a doctrine that infers negligence from the very nature of an accident or injury in the absence of direct evidence on how any defendant behaved. Although modern formulations differ by jurisdiction, common law originally stated that the accident must satisfy the necessary elements of negligence: duty, breach of duty, causation, and injury. In res ipsa loquitur, the elements of duty of care, breach and causation are inferred from an injury that does not ordinarily occur without negligence.

The term comes from Latin and is literally translated "the thing itself speaks", but the sense is well conveyed in the more common translation, "the thing speaks for itself." The earliest known use of the phrase was by Cicero in his defence speech Pro Milone. The circumstances of the genesis of the phrase and application by Cicero in Roman legal trials has led to questions whether it reflects on the quality of res ipsa loquitur as a legal doctrine subsequent 52 BC, some 1915 years before the English case Byrne v Boadle and the question whether Charles Edward Pollock might have taken direct inspiration from Cicero's application of the maxim in writing his judgment in that case.

The first element may be satisfied in one of three ways:

(a) The injury itself is sufficient to prove blatant or palpable negligence as a matter of law, such as amputation of the wrong limb or leaving instruments inside body after surgery.

(b) The general experience and observation of mankind is sufficient to support the conclusion that the injury would not have resulted without negligence, such as a hysterectomy (removal of the uterus) was performed when the patient consented only to a tubal ligation (clipping of the fallopian tubes for purposes of sterilization).

(c) Expert testimony creates an inference that negligence caused the injury, such as an expert general surgeon testifying that he has performed over 1000 appendectomies (removal of the appendix) and has never caused injury to a patient's liver. He also does not know of any of his surgeon colleagues having inflicted injury to a patient's liver during an appendectomy. The testimony would create an inference that injuring the liver in the course of an appendectomy is negligence.

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