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A Phrase in Latin: Res Ipsa Loquitur


A Phrase in Latin: Res Ipsa Loquitur


The last chapter considered the use of statutory standards of care to prove that the defendant breached the duty of due care or “was negligent.” This chapter considers another means of proving negligence, through the mystic doctrine of res ipsa loquitur.

Sometimes proving negligence is straightforward. Suppose that Cis-neros goes to the neighborhood garage to have the wheels of his Maserati balanced. After driving away, the right front wheel falls off. Cisneros gets out and looks around, but is only able to find three of the lug nuts that hold the wheel on. He returns to the station, where another customer tells him that he saw the mechanic leave the other lug nuts off. Negligence? No problem: What happened is clear from direct evidence, the testimony of the other customer, and a jury would almost certainly conclude that the mechanic was negligent in failing to replace all the lug nuts.

Would that all negligence cases were so easy. If they were, few negligence cases would be tried, because cases in which liability is clear almost always settle before trial. The cases that reach the trial stage are likely to present substantial disputes of fact, in which proof of essential elements-particularly negligence-is more problematic.


In the Maserati example, Cisneros produces compelling evidence of the mechanic’s negligence, direct testimony from a witness who observed the negligent act. However, negligence need not always be proved by direct evidence. In many cases, plaintiffs will have to rely on “circumstantial” evidence, that is, evidence of facts from which a jury could infer that the defendant was negligent. Cisneros might, for example, return to the garage and find two Maserati lug nuts sitting next to the wheel balancing apparatus. This might suffice to allow a jury to infer negligence on the part of the mechanic. The argument runs like this: If the wheel fell off shortly after Cisneros drove away, and if two Maserati lug nuts were sitting at the garage, and if Cisneros could only find three at the scene, it is likely that the mechanic only refastened three. Common experience tells us that leaving some of the lug nuts off creates an unreasonable risk that the wheel will come loose. Therefore, it appears probable that the mechanic was negligent in failing to secure the wheel.

Cisneros might have to rely on even less compelling circumstantial evidence to establish negligence. He might only be able to prove that the wheel fell off shortly after he left the garage, and that he was unable to locate all the lug nuts at the scene of the accident. This does not directly show that the mechanic failed to refasten them, but it again suggests (though less forcefully than the last scenario) that the likely explanation of the accident is the failure to refasten all the lug nuts. A jury could still reasonably infer from the facts Cisneros has proved that the accident more probably than not happened because the lug nuts were not refastened or were improperly fastened. Thus, proof of the circumstances allows an inference of further facts which would establish the mechanic’s negligence.

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