Well, they don’t know that negligence was involved, of course. On the other hand, they don’t know what caused the accident in the Maserati example, either; they simply make a reasonable estimate of the probabilities based on what they do know. Similarly, in res ipsa loquitur cases, the jury may not be able to reconstruct the sequence of events, but they may be able to make an educated inference that, whatever it was, it probably involved the defendant’s failure to exercise due care in some respect. The inference may not be infallible, it may not be satisfying to the ruthlessly syllogistic mind, but it is accepted by the legal system as sufficient to satisfy the “more probable than not” standard of proof in negligence cases. Courts, as practical institutions, must face the fact that irrefutable proof is seldom available in practical affairs, that the system is imperfect by its nature and must settle for a reasonable balance of the probabilities. “Res ipsa by its nature deals with mysteries and the efforts of imperfect legal processes to unravel them.” M. Shapo, Principles of Tort Law 255.
Consider the alternative. The judicial system could send Byrne away empty handed, explaining the result to him thus:
Sorry, Byrne, about your busted boodle. But we aren’t willing to make Boadle pay you unless you show that he did something wrong. You haven’t met your burden of proof, because you haven’t shown us what specific act Boadle did that was negligent. Unless you produce such evidence, you are not entitied to recover.
This reasoning sounds pretty good, but it doesn’t comport with most people’s sense of elementary fairness. Most people would make the inference that Boadle or his employees must have done something negligent for that barrel to get loose, even if we don’t know exactly what it was. Similarly, most people would infer that the platform collapse was caused by faulty construction, or that the brick fell because of negligence. The res ipsa loquitur doctrine allows juries to make the same inference of negligence that most of us would make from our common experience.
Not every plaintiff can get to the jury by intoning the magic Latin, however. For the res ipsa doctrine to apply, the circumstances must support an inference of negligence:
There must be reasonable evidence of negligence. But where the thing is shown to be under the management of the defendant or his servants, and the accident is such as in the ordinary course of things does not happen if those who have the management use proper care, it affords reasonable evidence, in the absence of explanation by the defendants, that the accident arose from want of care.
Scott v. London & St. Katherine Docks Co., 159 Eng. Rep. 665, 667 (1865). This early statement of the doctrine remains essentially intact. Most courts hold that the plaintiff can make a case for the jury under res ipsa loquitur by showing first that he was injured by an accident that would not ordinarily happen without negligence and second that the negligence is more likely than not attributable to the defendant, rather than to the plaintiff or a third party.