The doctrine of res ipsa loquitur, means the thing speaks for itself. Under the doctrine of res ipsa loquitur a plaintiff establishes a prima facie case of negligence where,
(I) it is not possible for him to prove precisely what was the relevant act or omission which set in train the events leading to the accident, and
(2) on the evidence as it stands at the relevant time it is more likely than not that the effective cause of the accident was some act or omission of the defendant or of someone for whom the defendant is responsible, which act or omission constitutes a failure to take proper care for the plaintiff’s safety. There must be reasonable evidence of negligence.
Conditions to attract applicability
Three conditions must be satisfied to attract applicability of res ipsa loquitur:
(i) the accident must be of a kind which does not ordinarily occur in the absence of someone’s negligence;
(ii) it must be caused by an agency or instrumentality within the exclusive control of the defendant;
(iii) it must not have been due to any voluntary action or contribution on the part of the plaintiff.
Supreme Court’s on Principle
In Krishna Bus Service Ltd vs Smt Mangli and others , their Lordships have stated the principle as under :-
“Wherein an action for negligence the thing causing fatal injury to the deceased and consequent pecuniary loss to the plaintiff is shown to be under the management of the defendant or his servants and the accident is such as in the ordinary course of events does not happen if those who have the management use proper care, that affords reasonable evidence, in the absence of the explanation by the defendants, that the accident arose from want of care.”
In Sham Sunder vs. State of Rajasthan, their Lordships held that the maxim did not embody any rule of substantial law nor a law of evidence; it was simply `the caption to an argument on the evidence’. Their Lordships further held: –
“The maxim res ipsa loquitur is resorted to when an accident is shown to have occurred and the cause of the accident is primarily within the knowledge of the defendant. The mere fact that the cause of the accident is unknown does not prevent the plaintiff from recovering the damages, if the proper inference to be drawn from the circumstances which are known is that it was caused by the negligence of the defendant. The fact of the accident may, sometimes, constitute evidence of negligence and then the maxim res ipsa loquitur applies.
The principal function of the maxim is to prevent injustice, which would result if a plaintiff were invariably compelled to prove the precise cause of the accident and the defendant responsible for it even when the facts bearing on these matters are at the outset unknown to him and often within the knowledge of the defendant.”
“The plaintiff merely proves a result, not any particular act or omission producing the result. If the result, in the circumstances in which he proves it, makes it more probable than not that it was caused by the negligence of the defendant, the doctrine of res ipsa loquitur is said to apply, and the plaintiff will be entitled to succeed unless the defendant by evidence rebuts that probability.”
Klaus Mittelbachert vs East India Hotels Ltd.: 1999 ACJ 287
 Ratanlal & Dhirajlal on Law of Torts edited by Justice G.P. Singh, 22nd edition 1992, pp 499-501 and the Law of Negligence by Dr Chakraborti, 1996 edition , pp 191-192