A 1938 railroad case still decides whose law your federal court applies.

Tompkins won $30,000 before Erie took the judgment away

On a dark night in 1934, Harry Tompkins was walking along a railroad right of way at Hughestown, Pennsylvania, when a passing Erie Railroad freight train struck him. He said he was rightfully on the premises as a licensee because he was using "a commonly used beaten footpath" that ran for a short distance beside the tracks. He said something that looked like "a door projecting from one of the moving cars" hit him.

Tompkins was a Pennsylvania citizen. He sued the Erie Railroad Company in the federal court for the Southern District of New York, which had jurisdiction because Erie was a corporation of that State. That was diversity jurisdiction.

The dispute concerned more than the railroad's conduct. Erie argued that Pennsylvania law treated people who used a path running along a railroad right of way, a longitudinal pathway as distinguished from a crossing, as trespassers. Under that rule the railroad would not be liable for injuries to undiscovered trespassers caused by its negligence unless its conduct was wanton or wilful.

Tompkins denied that Pennsylvania's courts had established any such rule. He argued that Pennsylvania had no statute on the subject, so the federal court could determine the railroad's duty as a matter of general law.

The trial judge declined to rule that Pennsylvania law barred recovery. A jury returned a verdict of $30,000. The Circuit Court of Appeals for the Second Circuit affirmed, 90 F.2d 603, holding that it was unnecessary to decide whether the law of Pennsylvania was as Erie contended, because the question was one not of local but of general law.

The Supreme Court reversed. Tompkins had won at trial and on the first appeal. The decision that carries his name took that judgment away from him.

Erie rejected ninety-six years of federal general law

Erie Railroad Co. v. Tompkins, 304 U.S. 64 (1938), was argued January 31 and decided April 25, 1938. Justice Brandeis delivered the opinion of the Court. Justice Butler dissented, joined by Justice McReynolds. Justice Cardozo took no part in the consideration or decision of the case.

The case turned on section 34 of the Federal Judiciary Act of September 24, 1789, then codified at 28 U.S.C. § 725 and known as the Rules of Decision Act. The statute directed federal courts to regard the laws of the several States as rules of decision in trials at common law, in cases where they apply, unless the Constitution, a treaty or a federal statute required otherwise. The provision survives today as 28 U.S.C. § 1652.

The Court held that the federal courts had misread it. Since 1842, Swift v. Tyson, 16 Pet. 1, an opinion by Justice Story, had treated federal courts sitting in diversity as free, in matters of general jurisprudence, to exercise an independent judgment about what the common law is or should be, rather than applying the unwritten law of the State as declared by its highest court.

Erie overruled Swift. In the passage the case is remembered for, the Court wrote that "There is no federal general common law." Except where the Federal Constitution or an Act of Congress controls, the law applied in a case is the law of the State, and whether that law is declared by a legislature in a statute or by the State's highest court in a decision is not a matter of federal concern.

The Court added that Congress has no power to declare substantive rules of common law applicable within a State, whether local or general, commercial law or a part of the law of torts, and that no clause of the Constitution purports to confer such a power on the federal courts. It did not hold section 34, or any other Act of Congress, unconstitutional. It held only that in applying the Swift doctrine the courts had invaded rights reserved by the Constitution to the several States.

As an illustration of what the old rule produced, the Court pointed to Black & White Taxicab & Transfer Co. v. Brown & Yellow Taxicab & Transfer Co., 276 U.S. 518, where a party reincorporated in another State in order to reach a federal court that would apply a more favorable view of the general law.

The working rules that grew on top of it

Erie supplied the basic division between state law and federal law. Three later decisions built the machinery practitioners actually use.

In Klaxon Co. v. Stentor Electric Manufacturing Co., 313 U.S. 487, decided June 2, 1941, the Court held that a federal court sitting in diversity must follow the conflict-of-laws rules of the State where it sits and may not devise its own. The forum State's rules therefore select which State's substantive law applies.

Guaranty Trust Co. v. York, 326 U.S. 99, decided June 18, 1945, produced what became known as the outcome-determinative test. In a suit on a state-created right where jurisdiction rested solely on diversity, there could be no recovery if a state statute of limitations would have barred the suit in the State's own courts.

Hanna v. Plumer, 380 U.S. 460, decided April 26, 1965, addressed a different question. Service had been made under Federal Rule of Civil Procedure 4(d)(1) by leaving the papers with the defendant's wife at his residence, while Massachusetts law required in-hand service on the defendant. The Court held that in a diversity case the adequacy of service is measured by the Federal Rules, and that where a valid Federal Rule covers the disputed point, the Erie analysis is not the test. At 380 U.S. 468 the Court named what it called the twin aims of the Erie rule: "discouragement of forum-shopping and avoidance of inequitable administration of the laws."

In Shady Grove Orthopedic Associates, P.A. v. Allstate Insurance Co., 559 U.S. 393, decided March 31, 2010, the Court held that Federal Rule of Civil Procedure 23 governs whether a class action may be maintained in federal court, displacing a New York statute that barred class actions to recover a statutory penalty.

What it decided in January 2026

The Supreme Court returned to the same problem in Berk v. Choy, No. 24-440, 607 U.S. 187 (2026), argued October 6, 2025 and decided January 20, 2026. Justice Barrett delivered the opinion of the Court, joined by Chief Justice Roberts and Justices Thomas, Alito, Sotomayor, Kagan, Gorsuch and Kavanaugh. Justice Jackson filed an opinion concurring in the judgment.

While on a trip to Delaware, Harold Berk fell out of bed. According to his complaint he was taken by ambulance to a hospital owned by Beebe Medical Center, Inc., where an X ray revealed a fractured ankle, and Dr. Wilson Choy recommended a protective boot. The fitting did not go well. Hospital employees forced Berk's leg into the boot, twisting the fractured ankle, and Dr. Choy did not immediately order another X ray.

Delaware law provides that a plaintiff may not sue for medical malpractice unless a medical professional attests to the suit's merit in an affidavit that accompanies the complaint. Del. Code, Tit. 18, § 6853(a)(1). Berk did not provide one. The District Court dismissed his suit for failure to comply, and the Third Circuit affirmed.

The Supreme Court reversed and remanded. Delaware's affidavit law does not apply in federal court.

The syllabus frames the reasoning as a choice-of-law problem. The Rules of Decision Act, 28 U.S.C. § 1652, directs federal courts to apply state substantive law unless the Constitution, a treaty or a statute otherwise requires or provides. The Rules Enabling Act, 28 U.S.C. § 2072(a), authorizes the Supreme Court to adopt uniform rules of procedure for the district courts, and § 2072(b) requires that those rules be procedural rather than substantive. So when a valid Federal Rule of Civil Procedure is on point, it displaces contrary state law even if the state law would qualify as substantive under Erie.

The Court calls the analysis straightforward. It asks first whether a Federal Rule answers the disputed question. If one does, the Rule governs unless it "exceeds statutory authorization or Congress's rulemaking power."

Rule 8 answered it. Rule 8(a)(2) requires a short and plain statement of the claim showing that the pleader is entitled to relief, and by requiring no more than that, it establishes that evidence of the claim is not required at the outset. Rule 12 reinforces the point by supplying only one ground for dismissal based on the merits, failure to state a claim under Rule 12(b)(6), and by prohibiting courts from considering matters outside the pleadings when they evaluate that question, under Rule 12(d). Delaware's law and Rule 8 therefore gave different answers to the same question. Rule 8 is valid under the Rules Enabling Act, the Court held, because it "really regulates procedure," and the argument that validity turns on whether the displaced state law is substantive was rejected.

The syllabus cites Erie Railroad Co. v. Tompkins, 304 U.S. 64, on its first page. The 1938 decision is not background in Berk. It is the operative citation.

The federal forum still changes the first question

Practitioner analyses of the decision count 28 states with affidavit-of-merit or certificate-of-merit statutes for malpractice claims. That count comes from firm commentary rather than from the Court. Those requirements continue to apply in the state courts of those States. Berk addressed federal court. Firm analyses have also flagged other state preconditions to suit as places the same question is likely to be asked, and the decision does not resolve any of them.

A note on how this piece was checked before it ran. The 1938 opinion was read page by page from the Library of Congress scan of the official United States Reports rather than from a case-brief summary, which is where the place name is printed as "Hughestown." One detail was cut for the same reason it was checked: the opinion never says which of Tompkins's arms was injured, and two otherwise reputable secondary accounts disagree, so this article does not say either. The January 2026 slip opinion was read from the Court's own PDF on supremecourt.gov, where Erie appears by name on the first page of the syllabus. The same method produced an earlier piece here ona three-sentence report from 1796that still anchors the American Rule on attorney's fees.

The first question in a state-law claim filed in federal court is whose law answers it.

The answer still starts with a 1938 opinion about a man on a footpath.