Res Ipsa Loquitur

Res ipsa loquitur is usually used when there is no direct evidence of the defendant's negligence. The facts presented to the court must meet the three basic requirements. Once the court decides that the facts of a particular case warrant the application of res ipsa, it instructs the jury on the basic principles, but it is the function of the jury to decide the credibility and weight of the inference to be drawn from the known facts. The jury can conclude that the defendant was negligent, but the jury is not compelled to do so. Everything depends upon the particular facts of each case. An inference of negligence might be so clear that no reasonable person could fail to accept it. If the defendant offers no explanation, the court can direct a verdict for the plaintiff if the inference is so strong that reasonable jurors could not reach any other conclusion. Where the jury considers the question of negligence, it can decide that the facts do not logically lead to an inference of the defendant's negligence, even if the defendant did not offer any evidence in her defense. If the defendant presents evidence that makes it unlikely that she has acted negligently, the plaintiff will lose his case unless he can rebut the evidence, since such evidence destroys the inference of negligence created by res ipsa.

A minority of courts hold that res ipsa creates a rebuttable presumption of negligence. Unless the defendant offers sufficient evidence to contradict it, the court must direct a verdict for the plaintiff. Some states have gone as far as to shift the burden of proof to the defendant, requiring her to introduce evidence of greater weight than that of the plaintiff.