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What is res ipsa loquitur in California?

California · updated 2026-09-01 · 710 words · 3 authorities cited

Res ipsa loquitur is a doctrine that allows a plaintiff to prove negligence through circumstantial evidence when the exact cause of an injury is unknown. It creates a permissive inference of negligence if certain conditions are met, shifting the burden to the defendant to provide an explanation. The doctrine is applicable in general negligence cases and has a specific formulation for medical malpractice.

The rule

A plaintiff may prove that a defendant's negligence caused harm if the plaintiff proves all of the following: (1) the harm ordinarily would not have happened unless someone was negligent; (2) the harm was caused by something that only the defendant controlled; and (3) the plaintiff's voluntary actions did not cause or contribute to the event that harmed the plaintiff 1. If these three elements are proven, the jury may, but is not required to, find that the defendant was negligent or that the defendant's negligence was a substantial factor in causing the plaintiff's harm, or both 1. If the plaintiff does not prove one or more of these three things, the jury must decide whether the defendant was negligent in light of other instructions 1.

In medical malpractice cases, the rule is similar but with specific adaptations: a plaintiff may prove that a defendant's negligence caused harm if the plaintiff proves all of the following: (1) the harm ordinarily would not have occurred unless someone was negligent; (2) the harm occurred while the plaintiff was under the care and control of the defendant; and (3) the plaintiff's voluntary actions did not cause or contribute to the event that harmed the plaintiff 2. For the first element in medical malpractice cases, the jury must consider only the testimony of expert witnesses 2. If these three elements are proven, the jury may, but is not required to, find that the defendant was negligent or that the defendant's negligence was a substantial factor in causing the plaintiff's harm, or both 2.

How it applies

The doctrine of res ipsa loquitur provides a way for a plaintiff to establish negligence when direct evidence of the defendant's negligent act is unavailable [1, 2]. It allows for an inference of negligence based on the circumstances surrounding the injury [1, 2]. The first element requires that the type of harm suffered does not typically occur without someone being negligent [1, 2]. For medical malpractice claims, expert testimony is specifically mandated to establish this point 2. The second element focuses on control, requiring that the instrumentality causing the harm was under the exclusive control of the defendant 1. In medical malpractice, this is framed as the harm occurring while the plaintiff was under the care and control of the defendant 2. The third element ensures that the plaintiff's own actions did not contribute to the event causing the harm [1, 2].

If a plaintiff successfully proves all three conditions, the jury is permitted, but not compelled, to find negligence [1, 2]. This means that even if the conditions are met, the jury still has the discretion to decide whether negligence occurred [1, 2]. The defendant may present evidence to rebut the inference of negligence [1, 2]. If the jury believes it is more probable than not that the defendant was negligent and that this negligence was a substantial factor in causing harm, they must decide in favor of the plaintiff [1, 2]. Otherwise, they must decide in favor of the defendant [1, 2].

The doctrine of res ipsa loquitur can also impact procedural requirements in certain professional negligence cases. For instance, in actions against architects, professional engineers, or land surveyors, if an attorney intends to rely solely on the doctrine of "res ipsa loquitur," a certificate of merit is not required 3. The attorney must certify upon filing the complaint that they are solely relying on this doctrine 3.

What this does not cover

The provided sources do not cover the historical development of the res ipsa loquitur doctrine, specific examples of its application in various factual scenarios beyond the general and medical malpractice contexts, or detailed appellate court interpretations of the elements. The sources also do not address how the doctrine interacts with other specific defenses or evidentiary rules, beyond the mention of expert testimony in medical malpractice.

Authorities cited

1. CACI 417

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2. CACI 518

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3. CCP 411.35

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