Res ipsa Loquitur. Module 4

In the common law of negligence, the doctrine of res ipsa loquitur (Latin for "the thing speaks for itself") states that the elements of duty of care and breach can be sometimes inferred from the very nature of an accident or other outcome, even without direct evidence of how any defendant behaved. Although modern formulations differ by jurisdiction, the common law originally stated that the accident must satisfy the following conditions:
1. A "duty" exists for a person to act "reasonably"; and
2. A "breach" of this duty occurs because a person [or agency, etc.] acted outside this duty, or "unreasonably"; and
3. There was "causation in fact"...the result would not have occurred "but for" the "breach" of this duty;
4. There was actual legally recognizable harm suffered by the plaintiff who did nothing wrong (i.e., no contributory negligence).
Upon a proof of res ipsa loquitur, the plaintiff need only establish the remaining two elements of negligence—namely, that the plaintiff suffered harm, of which the incident result was the legal cause.

The term comes from Latin and is literally translated "the thing itself speaks", but the sense is well conveyed in the more common translation, "the thing speaks for itself." The earliest known use of the phrase was by Cicero in his speech Pro Milone.

The legal doctrine was first formulated by Baron Pollock in the 1863 English case Byrne v Boadle.

Exclusive control
In some cases a closed group of people may be held in breach of a duty of care under the rule of res ipsa loquitur. In Ybarra v. Spangard, a patient undergoing surgery experienced back complications as a result of the surgery, but it could not be determined exactly which member of the surgical team had breached his or her duty, and so it was held that they had all breached, because it was certain that at least one of them was the only person who was in exclusive control of the instrumentality of harm.
Because it can be difficult to prove "exclusive control", this element has largely given way in modern cases to a less rigid formulation: that the evidence eliminates, to a sufficient degree, other responsible causes (including the conduct of the plaintiff and third parties). For example, in New York State, the defendant's exclusivity of control must be such that the likelihood of injury was, more likely than not, the result of the defendant's negligence. The likelihood of other possibilities do not need to be eliminated altogether but they must be so reduced that the greater probability lies with the defendant.

Plaintiff did not contribute
In jurisdictions that employ this less rigid formulation of exclusive control, this element subsumes the element that the plaintiff did not contribute to his injury.
In modern case law, contributory negligence is compared to the injury caused by the other. For example, if the negligence of the other is 95% of the cause of the plaintiff's injury, and the plaintiff is 5% responsible, then the plaintiff's slight fault cannot negate the negligence of the other. This new type of split liability is commonly called comparative negligence. As a fictitious example:
John Doe is injured when an elevator he has entered plunges several floors and stops abruptly.
Jane's Corporation built, and is responsible for maintaining, the elevator.
Doe sues Jane, and during the proceedings, Jane claims that Doe's complaint should be dismissed because he has never proved, or for that matter even offered, a theory as to why the elevator functioned incorrectly. Therefore, argues Jane, there is no evidence that they were at fault.
The court holds that Doe does not have to prove anything beyond the fall itself.
The elevator evidently malfunctioned (it was not intended to fall nor is that a proper function of a correctly functioning elevator).
Jane was responsible for the elevator in every respect
So Jane's Corporation is responsible for the fall.
The thing speaks for itself: no further explanation is needed to establish the prima facie case.