As Justice Shaw made clear in Brown v. Kendall (Chapter 4), it is the plaintiff's burden to prove negligence. In some cases, however, only circumstantial evidence of negligence is available to the plaintiff. If courts demanded that plaintiffs prove negligence in every case, plaintiffs would lose most negligence suits based on circumstantial evidence. The defendant could prevail simply by asserting that the plaintiff had not proved his case.

To avoid this outcome, courts have developed a special doctrine of inference for negligence cases. The label for this doctrine, res ipsa loquitur, means “the thing speaks for itself.” The doctrine of res ipsa loquitur consists of rules that guide courts in their disposition of negligence cases involving circumstantial evidence.

In general, courts dispose of negligence cases involving circumstantial evidence by dismissing the plaintiff's case, allowing the case to reach a jury, or issuing a directed verdict in favor of the plaintiff. The core issue in res ipsa loquitur cases is whether the evidence is sufficient to warrant submission of the plaintiff's case to a jury.

Given the importance of the jury to this topic I will start with a brief review of the respective roles of judge and jury in negligence cases before introducing res ipsa loquitur doctrine.

JUDGE AND JURY: A BRIEF OVERVIEW

Legal disputes present questions of law, questions of fact, and mixed questions of law and fact. In theory, these questions could be answered by a judge or by a jury.

A question of fact is one that can be answered without any reference to the law. Suppose the defendant says that he was on the corner of Main Street and Elm Street at 8:00 a.m. on Tuesday morning, and the plaintiff says that the defendant was not on that corner at that time. Since this is a disputed question of fact, some decision maker in the court, either judge or jury, has to determine which factual claim the court will accept as valid.

A pure question of law is one that can be answered without any reference to the facts in a dispute. Suppose the defendant argues that to be held liable for battery there must be evidence that he intended to harm the plaintiff (see Vosburg v. Putney, Chapter 4).