res ipsa loquitor

noun | \-ˈlō-kwə-tər\ | res ipsa lo·qui·tur

1. : a doctrine or rule of evidence in tort law that permits an inference or presumption that a defendant was negligent in an accident injuring the plaintiff on the basis of circumstantial evidence if the accident was of a kind that does not ordinarily occur in the absence of negligence a plaintiff who establishes the elements of res ipsa loquitur can withstand a motion for summary judgment and reach the jury without direct proof of negligence —Cox v. May Dept. Store Co., 903 P.2d 1119 (1995)

   Note: For res ipsa loquitur to apply, the accident in question must not be due to any voluntary action or contribution by the plaintiff. The doctrine has traditionally required that a defendant have exclusive control over the instrumentality of an injury, but now it is commonly applied when multiple defendants have joint or sometimes successive control (as by the manufacturer and retailer of a defective product). In addition to the control requirement, and sometimes superseding it, is the requirement that a defendant have responsibility for the instrumentality as well as responsibility to the plaintiff. In order for res ipsa loquitur to succeed in a medical malpractice suit, the fact that the accident is one that ordinarily does not occur without a failure to exercise due care must be readily apparent to the layperson as common knowledge. The accident alone should afford reasonable evidence of negligence, as when a foreign object is left inside a surgical patient.