Is res ipsa a separate cause of action that can be pled?
No, res ipsa loquitur is not a separate cause of action that can be pled in a complaint. It is an evidentiary doctrine within negligence law, not an independent tort or claim.
Issue
Whether the doctrine of res ipsa loquitur can be alleged as a stand-alone cause of action in a civil complaint.
Rule
The U.S. Supreme Court in Sweeney v. Erving, 228 U.S. 233 (1913) established that res ipsa loquitur “means that the facts of the occurrence warrant the inference of negligence, not that they compel such an inference.” The doctrine does not shift the burden of proof and does not create a new cause of action—it is a rule of circumstantial evidence used to infer negligence where direct proof is lacking.[4] Likewise, Pennsylvania courts treat res ipsa loquitur as “nothing more than a rule of circumstantial evidence” rather than a substantive claim.
Application
Under Pennsylvania law and in the Third Circuit, res ipsa loquitur provides a permissible inference of negligence when (1) the event is of a type that does not ordinarily occur without negligence, (2) the instrumentality causing the harm was within the defendant’s exclusive control, and (3) the injury was not due to the plaintiff’s voluntary action or contribution.[5] These elements allow a jury to infer negligence from the mere occurrence of an accident, but the inference arises within the framework of an existing negligence claim.
Thus, res ipsa loquitur operates at the evidentiary stage—it affects the proof, not the pleadings. A plaintiff must still allege and prove negligence as the underlying cause of action. Courts consistently hold that a complaint cannot assert “res ipsa loquitur” as a separate count, though plaintiffs may allege facts suggesting the doctrine’s applicability or reference it to support an inference of negligence.[2][3]
Federal pleading principles under Fed. R. Civ. P. 8(a) and Pennsylvania’s Rule of Civil Procedure 1019 likewise require only a short statement of the claim showing entitlement to relief. Since res ipsa loquitur does not itself create liability, but only defines how evidence may establish it, it cannot serve as the basis of a claim.
Conclusion
Res ipsa loquitur is not a separate cause of action that can be pled in a complaint. It is a rule of evidence within negligence law that allows an inference of negligence under certain proven circumstances. Plaintiffs must plead negligence as the cause of action and may rely on res ipsa loquitur at trial to establish it.
[1] Sweeney v. Erving, 228 U.S. 233 (1913).
[2] Pleading in Res Ipsa Loquitur Cases, Knowledge Bank (Ohio State University).
[3] Third Circuit Invokes Res Ipsa Loquitur in FELA Case, 3 U. Pa. L. Rev.
[4] Jones v. Harrisburg Polyclinic Hosp., 437 A.2d 1134 (Pa. 1981).
[5] Toogood v. Owen J. Rogal, D.D.S., P.C., 824 A.2d 1140 (Pa. 2003).
Lageman v. Zepp, No. J-60-2021 (Pa. 2021) (reaffirming that res ipsa loquitur is a rule of circumstantial evidence).