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When Does “Res Ipsa Loquitur” Apply in California?

Posted by Dmitry Gorin | Nov 18, 2023

Res ipsa loquitur is Latin for “the thing speaks for itself.” This legal doctrine applies when an accident suggests negligence and a plaintiff must rely on circumstantial evidence to prove a defendant's negligence.

Common in medical malpractice cases, res ipsa loquitur shifts the burden of proof to the defendant. While the plaintiff generally has the burden of proving a defendant's negligence, the defendant must show why they were not negligent in these cases.

When Does “res ipsa loquitur” apply in California?

Simply put, In California, res ipsa loquitur is a legal doctrine allowing accident victims to prove someone was negligent by the mere fact there is no other reasonable explanation. In other words, the only logical conclusion based on the available evidence is that the defendant is liable.

However, to win a personal injury claim in California based on res ipsa loquitur, you must prove the accident or injury would not ordinarily have occurred without negligence, the incident causing your injury was under the defendant's control, and you did nothing to cause the harm.

Once this claim is made, the burden shifts to the defendant to prove they were not responsible. If they cannot do this, you could be successful in winning the case.

Notably, however, proving res ipsa loquitur can be challenging to prove. For example, suppose it's clear that somebody was negligent. Still, it's not always easy to establish precisely who it was.

In California, medical malpractice and car accidents are typical cases in which you might consider using res ipsa loquitur. Still, it could also be used in other injury cases, such as product liability.

What is Res Ipsa Loquitur in California?

California Evidence Code 646 refers to res ipsa loquitur as “a presumption affecting the burden of producing evidence.”

“(a) As used in this section, “defendant” includes any party against whom the res ipsa loquitur presumption operates.

(b) The judicial doctrine of res ipsa loquitur is a presumption affecting the burden of producing evidence.

(c) If the evidence, or facts otherwise established, would support a res ipsa loquitur presumption and the defendant has introduced evidence that would support a finding that he was not negligent or that any negligence on his part was not a proximate cause of the occurrence, the court may, and upon request shall, instruct the jury to the effect that:

(1) If the facts that would give rise to res ipsa loquitur presumption are found or otherwise established, the jury may draw the inference from such facts that a proximate cause of the occurrence was some negligent conduct on the part of the defendant and

(2) The jury shall not find that a proximate cause of the occurrence was some negligent conduct on the part of the defendant unless the jury believes after weighing all the evidence in the case and drawing such inferences from that place as the jury believes are warranted, that it is more probable than not that some negligent conduct on the part of the defendant caused the occurrence.”

What Is No Other Reasonable Explanation?

Moreover, no other reasonable explanation exists for the cause of the plaintiff's injury. To use res ipsa loquitur, a plaintiff must supply evidence that establishes:

  • The events or injuries are unlikely to occur without negligence;
  • The events or situation that led to the injury were under the defendant's exclusive control;
  • The plaintiff's actions or lack of actions did not cause the injury.

If successful, the burden moves to the defendant, who must show that they were not negligent, or even if they were negligent, it did not cause the plaintiff's injury.

As in all personal injury cases and as mentioned above, a link must be shown between the defendant's negligence and the plaintiff's injury. Without proving this element, a plaintiff is unlikely to win a case.

The difficulty of res ipsa loquitur is that the case is one of assumption. In most personal injury cases, a plaintiff provides evidence that explicitly links a defendant's negligence to the plaintiff's injury.

The Difficulty of Res Ipsa Loquitur: An Example with Variations

Gary attends a food festival. He tries food from ten booths. At home that evening, he feels bad and goes to the ER. Tests determined he ingested a cleaning fluid that can be toxic to people.

That Gary's poisoning would not have occurred, but for someone's negligence, it should be easy to establish. Likewise, Gary did not do anything to cause his poisoning. Establishing the other elements depends on what further details and evidence Gay can find.

Res Ipsa Loquitur

One possibility is that other people report poisoning; the only commonality is one food vendor using that cleaning product. Here, Gary could likely use res ipsa loquitur to establish negligence.

In another possibility, multiple people report poisoning, but several frequented the same food vendors. Three of those vendors use the cleaning product. Gary may have difficulty connecting any one vendor as the proximate cause.

In a third variation, no other cases of illness or poisoning are reported. However, one doctor states that Gary's symptoms would have started within three hours of ingesting the cleaning agent, leaving only one possible vendor as the cause. In this case, Gary should be able to use res ipsa loquitur.

Similarly, no other cases of illness or poisoning are reported, and Gary only ate at one vendor within the onset window. In this version, however, the vendor shows that the festival provided cooking utensils for the vendors, meaning they were not under the vendor's exclusive control. Neither the vendor nor the festival used the cleaning product, but several other vendors did.

In this version, Gary would likely be unable to establish who was negligent or exclusive control. As these variations demonstrate, real-world events are complex. Using circumstantial evidence to connect negligence with a plaintiff's injury or prove negligence on the defendant's part can be challenging.

Medical Malpractice

One of the more common uses for res ipsa loquitur is medical malpractice when a patient is sedated. The patient/plaintiff is unlikely to have a way to link their post-sedation injury to the medical procedure. When multiple medical personnel were involved in a procedure, all share the responsibility for the negligence that caused the plaintiff's injury.

Some medical malpractice cases, such as operating on the wrong limb, are serious enough that juries will likely side with the plaintiff. Less severe injuries or those that don't have a clear link to a medical procedure, such as digestive issues or pain, may be more difficult for a plaintiff to establish.


Res ipsa loquitur allows the plaintiff to prove negligence based on circumstantial evidence. Depending on the specific details of any accident or injury, plaintiffs may have difficulty proving a defendant's exclusive control or establishing that the defendant was the primary cause of the plaintiff's injury.

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About the Author

Dmitry Gorin

Dmitry Gorin is a licensed attorney, who has been involved in criminal trial work and pretrial litigation since 1994. Before becoming partner in Eisner Gorin LLP, Mr. Gorin was a Senior Deputy District Attorney in Los Angeles Courts for more than ten years. As a criminal tri...


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