Res Ipsa Loquitur (What It Means And Why It’s So Important)

What does res ipsa loquitur mean?

How do you define it?

What are the elements you need to prove to create a presumption of negligence?

We will look at what res ipsa loquitur means, look at its origins, legal definition, look at how to prove a defendant’s negligence without having direct facts, how to defend against a res ipsa loquitur lawsuit, look at examples and more.

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The thing speaks for itself

Res ipsa loquitur (or res ipsa loquitor) is Latin for the thing speaks for itself or it speaks for itself.

Many lawyers and attorneys find it easier to refer to res ipsa loquitur as res ips or res ipsa as shorthand.

The res ipsa loquitur is an English tort law doctrine allowing a plaintiff in a tort lawsuit to prove tort or negligence using circumstantial evidence.

In other words, res ipsa loquitur does not require that the plaintiff prove the exact cause of negligence.

In the absence of direct evidence proving the defendant was negligent, the court can infer negligence by analyzing the evidence surrounding the accident or incident.

For example:

John gets into a car accident in the middle of the night injuring his friend Mary who was a passenger. 

Nobody witnessed the accident and Mary was sleeping when the accident happened.

Mary cannot directly prove John’s negligence but based on the circumstantial evidence, she can prove that John was negligent and liable for the damages caused.

At the moment of the accident, the car was under John’s control and, aside from John’s negligence, there are no other plausible explanations for the cause of the accident.

By proving the res ipsa loquitur elements, a plaintiff will establish a rebuttable presumption of negligence against the defendant.

Res ipsa loquitur definition

According to’s Legal Dictionary, res ipsa loquitur is defined as:

Latin for “the thing speaks for itself,” a doctrine of law that one is presumed to be negligent if he/she/it had exclusive control of whatever caused the injury even though there is no specific evidence of an act of negligence, and without negligence the accident would not have happened. 

What is notable with the res ipsa loquitur legal definition is that there is presumed negligence even though no specific evidence of an act of negligence is demonstrated.

The Merriam-Webster dictionary provides a legal definition of res ipsa loquitur as follows:

a doctrine or rule of evidence in tort law that permits an inference or presumption that a defendant was negligent in an accident injuring the plaintiff on the basis of circumstantial evidence if the accident was of a kind that does not ordinarily occur in the absence of negligence

With this evidentiary rule, the court can make an assumption of facts without having direct evidence.

Origins of the res ipsa doctrine

The res ipsa legal theory originates from the case Byrne v Boadle in 1863 when a barrel of flour fell from a building on the plaintiff’s head as he was passing by.

The court applied the res ipsa doctrine to hold the defendant, who was responsible for the barrel, liable for the plaintiff’s injuries.

When the accident occurred, there were no witnesses who witnessed the barrel fall or saw the plaintiff get injured by the falling barrel.

However, the court considered that the circumstantial evidence was sufficient to establish that the defendant breached its duty of care.

Res ipsa loquitur elements

To establish a presumption of negligence in tort law without having to prove an actual act of negligence, a plaintiff may invoke the doctrine of res ipsa loquitur to prove the following elements:

  • The accident or damages are generally caused by negligent acts or conduct (or this type of accident does not happen without someone’s negligence)
  • The incident occurred by an instrumentality solely under the control of the defendant
  • The plaintiff did not contribute to the incident or cause of the accident (or the plaintiff has ruled out the possibility that he or she, or a third party, was to blame for the accident)
  • The defendant owed the plaintiff a duty of care 

With regards to the instrumentality “solely” or “exclusively” under the control of the defendant, the courts have relaxed this requirement as it was a burden of proof too difficult to achieve for plaintiffs.

The plaintiff must prove that the defendant’s exclusivity of control explains the accident in the balance of probabilities 

The plaintiff does not need to completely prove that there were no other possible causes of the accident but rather demonstrate that the defendant’s exclusivity of control can explain the accident in all likelihood

In many common law jurisdictions, a plaintiff must prove the elements of negligence to obtain remedy or compensation for damages caused by the defendant, namely:

  • Defendant’s duty of care
  • Defendant’s breach of duty of care
  • Injury to the plaintiff
  • Causation between the defendant’s breach of duty of care and the plaintiff’s injuries 

What’s interesting with the res ipsa loquitur evidence law is that the court will infer the duty of care, breach of duty of care and the causation between the injuries suffered and the breach of duty of care.

Res ipsa loquitur shifts the burden of proof from the plaintiff to the defendant.

Once the plaintiff has demonstrated the elements of res ipsa loquitur, the defendant will then have the burden of proof to demonstrate that he or she was not negligent.

Defense against res ipsa loquitur

A defendant may defeat the res ipsa loquitur argument invoked by:

  • Demonstrating that the plaintiff’s actions or conduct contributed to the alleged injuries
  • By producing evidence of a non-negligence scenario that can explain the accident and injuries suffered by the plaintiff 
  • Demonstrating that he or she did not owe the plaintiff any duty of care

If the defendant is able to demonstrate other possible causes for the incident, then the court may no longer infer that the “only possible explanation” or “the most likely explanation” is the defendant’s presumed negligence.

In a personal injury lawsuit or cases of negligence, the plaintiff’s strategy will be to demonstrate that the circumstantial evidence points to the negligent actions or conduct of the defendant as the most logical conclusion or explanation for the accident.

The defendant must attack the plaintiff’s legal inference by using the totality of circumstances and the shared knowledge out of the human experience to provide for another plausible explanation or logical conclusion as to why the accident happened (without his or her negligence). 

Res ipsa loquitur vs prima facie

Let’s clear some confusion about “res ipsa loquitur” and “prima facie” evidence.

Prima facie in Latin means “at first sight”.

For a person to file a lawsuit against another or invoke a specific legal theory, there must be, at first sight, a minimum level of evidence for the case to be legally worth pursuing in court.

The court will dismiss, typically following the filing of a motion to dismiss, a lawsuit if it does not have prima facie merit or any meaningful chance of success on its merits.

On the other hand, res ipsa loquitur is a common law legal theory invoked in tort cases where a plaintiff provides compelling circumstantial evidence allowing the court to infer the defendant’s negligence.

The evidence is so obvious that it speaks for itself relieving the plaintiff from having to prove anything further.

Res ipsa loquitur examples

Let’s look at a few examples to see how we can use the res ipsa loquitur law to create a rebuttable presumption of negligence.

Medical malpractice

A common res ipsa loquitur example is in the area of medical malpractice.

The classical example is when a doctor performs the wrong operation on the patient.

The patient goes to be operated on for one thing and the doctor performs another operation causing bodily injuries.

In this type of case, there is a prima facie demonstration of the doctor’s liability as there are no other legitimate reasons for the doctor to perform an operation other than what was initially planned.


Another common example relates to damages or bodily injuries caused on construction sites.

Suzanne is injured on a construction site due to the malfunctioning of a crane.

Top Cranes Inc is the company that built the crane and is responsible for maintaining it.

Suzanne files a lawsuit against Top Cranes Inc for compensatory damages.

By invoking ipsa loquitur, Suzanne can hold Top Cranes Inc responsible by proving that the type of accident only happens through negligence in the way the crane was maintained, Top Cranes Inc was responsible for the cranes and there are no other plausible explanations for the accident.

Suzanne will present circumstantial evidence and state that the thing speaks for itself. 

Res ipsa loquitur FAQ

Res Ipsa Loquitur FAQ

What is the Latin phrase to say the thing speaks for itself

To say the thing speaks for itself in Latin, you must say ‘res ipsa loquitur’ or ‘res ipsa loquitur’.

The literal translation of res ipsa loquitur is “the thing itself speaks”.

However, its true meaning is “the thing speaks for itself”.

What does res ipsa loquitur mean

It is an evidentiary rule allowing the victim of an accident to establish a presumption of negligence on the part of the defendant considered to be at fault on the basis of circumstantial evidence.

Not all accidents result from someone’s negligence.

However, if the circumstantial evidence logically points to the defendant and provides a plausible explanation of the accident, in law, the burden of proof shifts from the plaintiff to the defendant who will need to demonstrate that he or she is not to blame for the accident.

When can you invoke res ipsa loquitur

“Res ipsa loquitur” is a common law doctrine typically invoked in:

  • Personal injury cases
  • Negligence cases or actions involving tort and tortious conduct
  • Medical malpractice
  • Product liability
  • Professional liability
  • Large-scale catastrophic accidents
  • Unsafe property cases

For example, if an airplane crashes due to its engines shutting off, the court can assume that this type of accident can only happen due to someone’s negligence. 

How do you pronounce res ipsa loquitur?

To pronounce res ipsa loquitur you must say “ress ipsah lokiter

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