There is nothing particularly mystical or sophisticated about this idea. As Lord Shaw quipped: “If that phrase had not been in Latin, no one would have called it a principle.” Ballard v. North British Ry. Co., 1923 Sess. Cas. 43 (1923). Res ipsa is not really a separate principle, but rather a special form of circumstantial evidence. The underlying rationale of res ipsa loquitur, as of circumstantial evidence in general, is that facts can sometimes be inferred from other facts. In a case like Cisneros’s tire problem, the circumstantial evidence allows the jury to infer a particular negligent act, failure to replace the lug nuts. In res ipsa loquitur cases, the circumstantial evidence allows the jury, based on evidence about the accident itself, to infer that it must have resulted from some negligent act by the defendant. In Byrne v. Boadle, for example, the circumstantial evidence that the barrel had fallen from the defendant’s second-story window sufficed to allow a jury to conclude that some negligent act by the defendant had caused it to fall.
Here are some other examples of cases in which the plaintiff might use res ipsa loquitur to establish negligence.
In each of these cases, there is no showing of exactly how the accident happened, but the fact that it happened at all suggests that someone was probably negligent.
We saw in Chapter 7 that the plaintiff must prove all the elements of a negligence claim in order to hold the defendant liable. Arguably, courts that apply res ipsa loquitur play fast and loose with the negligence element of the claim, since they allow the jury to find for the plaintiff without proving any specific negligent act. In the platform case, for example, if the plaintiff merely offers evidence that the platform fell shortly after it was constructed, he has not “proved” any particular negligent act by the contractor. Similarly, in the brick case, evidence that the brick fell while the defendant’s employees were working on the roof does not prove what negligent act (if any) caused it to fall. The jury cannot determine exactly what caused the brick to fall on the basis of such general evidence. How then, are they to know that there was negligence involved at all?