Topic: Res Ipsa Loquitur
In testing you on the doctrine of res ipsa loquitur, the examiners will, of course, be testing whether you know the requirements necessary for the doctrine to apply. Those requirements are as follows: (1): there is no direct evidence of the defendant's conduct; (2): the event that occurred ordinarily does not occur without negligence; (3): the instrument that caused the injury was in the direct control of the defendant; and (4): the injury was not due to the plaintiff's own actions.
Oftentimes, a question will be presented in which one of those elements above will be missing from the equation. Take, for example, the classic case of a supermarket customer slipping on a banana peel. Frequently, there is no direct evidence as to how the peel ended up where it ended up, and so in your mind you should be thinking that res ipsa loquitur might provide a basis for an inference of the supermarket's negligence even though there is no direct evidence of negligence on the part of the defendant (here, the supermarket).
But what if the facts provide that the banana peel looked as though it hadn't been on the floor for very long. In fact, nobody else had stepped on it, prior to the plaintiff's accident. In such a case, element (2) will be missing from the equation. If the banana peel had just dropped to the floor, then there is not a reasonable basis for inferring that the supermarket employees were negligent in not removing it from the floor (and inferences are the entire basis behind res ipsa loquitur). Even though it's quite possible that the three other elements have been satisfied, the fact that element (2) is not satisfied prevents the doctrine of res ipsa loquitur from applying.
Other questions will present situations in which one of the other elements is not satisfied (for example if the defendant was not in exclusive control of the instrumentality that caused the injury). As a general rule, apply all four elements carefully. If all apply, then negligence can be inferred, even if there is no direct evidence of the negligent act. If one or more elements is missing, no inference is allowable, and applying res ipsa loquitur is the incorrect response.