What is Res Ipsa Loquitur and When Can It Be Invoked?

The legal concept res ipsa loquitur can be difficult to understand if you are not familiar with legalese. In general, the meaning of res ipsa loquitur allows a plaintiff to ask the court to make assumptions of fact without direct evidence.

In doing so, the court finds the defendant in the case liable for your injuries. Courts in Pennsylvania tend to be wary of using it too much. However, it can be a useful tool if you are a plaintiff in a personal injury case.

Legal Terms

Res ipsa Loquitur, often shortened to “res ipsa” is a legal term that is used in personal injury cases to show evidence. Before understanding the res ipsa loquitur meaning, it is helpful to first define a few key legal terms that are often associated with it:

Negligence: In a personal injury case, a plaintiff usually claims that the defendant is guilty of some form of negligence that caused their injury. To establish negligence, the plaintiff must prove that someone or a company had a duty of care to act in a certain way. They must also show that they violated that duty and failed to act like a reasonable person would have in the same situation. Finally, because of this failure, the plaintiff suffered injury and harm that they would not have otherwise experienced.

Duty of care: This is a legal obligation that is imposed on a person or organization that requires them to follow a standard of reasonable care while doing an action that could foreseeably injure others.

Rebuttal presumption: This is an assumption of a fact that is accepted by the court until the opposing side offers evidence to the contrary. This means that the fact presented by the plaintiff is believed to be true by the court unless someone expressly comes forward to contest or prove the fact incorrect.

Circumstantial evidence: A type of evidence that implies a fact. It is not direct evidence like a fingerprint or a confession. Rather, it is several facts compiled together that indicate something is true. An example would be several witnesses observing a man running away from a murder scene while covered in blood. They did not directly see the man kill anyone but it could be inferred that he may be the killer from numerous witnesses giving testimony.

Res Ipsa Loquitur Meaning

Res Ipsa is used to determine negligence. It is important to note that not all accidents are caused by negligence. Even if an incident occurred and there were severe injuries, the court will not always assume that negligence was involved.

Generally, the plaintiff will need to establish that the defendant meets the elements of negligence. They will need to show that the defendant had a duty, that they breached the duty, and that there were injuries because of their breach.

In Latin, res ipsa loquitur translates to “the thing speaks for itself.” The concept allows a plaintiff in a case to establish a rebuttal presumption of negligence by using circumstantial evidence. In doing so, negligence is presumed because there is no other reasonable explanation for what happened.

When Can Res Ipsa Loquitur Be Invoked?

The elements needed to show res ipsa loquitur vary by state. In Pennsylvania, it is only applied sparingly.  It will only be applied if the plaintiff can show through circumstantial evidence that their injury was more likely than not caused by the defendant. In reality, it is a high standard to meet.  In general, the plaintiff must prove three things:

  •  The event that occurred would not normally happen unless there was some form of negligence;
  •  The plaintiff had a partial or total lack of fault in the negligence; and
  • The defendant had a duty of care.

The concept is most often invoked in cases of medical malpractice, product liability, and unsafe property. It is also used commonly in large-scale catastrophic accidents.

For example, if a train came off of its tracks and killed a dozen people, it would more than likely be assumed as fact that this type of incident would not have occurred but-for someone’s negligence. In general, trains do not come off of their tracks without some superseding negligent cause.

Pennsylvania courts have been wary of invoking res ipsa loquitur. In a case decided in 2017, a judge rejected the use of res ipsa loquitur because the circumstantial evidence offered by the plaintiff was expert testimony.

The court found that the testimony had several shortcomings and negligence could not be assumed based on the statement given by one expert. The testimony was declared inadmissible and the case was dismissed.


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Philadelphia, PA 19109
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