Subject-Matter Jurisdiction: Federal Question vs. Diversity (1L Civ Pro)

Subject-matter jurisdiction is a court's power to hear a particular type of case — power over the case, not over the parties (that's personal jurisdiction). For federal courts, this is a threshold question, because federal courts are courts of limited jurisdiction: they can only hear cases the Constitution and Congress have authorized.

That limitation is the whole game. A plaintiff who wants to be in federal court must point to a specific basis for subject-matter jurisdiction. The two you'll use constantly in 1L are federal question jurisdiction and diversity jurisdiction.

Two features make subject-matter jurisdiction unusual and very testable: it cannot be waived or consented to, and it can be raised by any party — or the court itself — at any time, even for the first time on appeal. A judgment entered without it can be vacated.

Under 28 U.S.C. § 1331, federal courts have jurisdiction over civil actions "arising under" the Constitution, laws, or treaties of the United States. The simplest case is a claim created by federal law — a federal statute that gives the plaintiff the right to sue.

The key wrinkle is the well-pleaded complaint rule from Louisville & Nashville Railroad v. Mottley. The federal question must appear on the face of the plaintiff's properly pleaded complaint — the part stating the plaintiff's own claim. It is not enough that a federal issue will come up as a defense, or that the plaintiff anticipates one.

So in Mottley, where the plaintiffs expected the railroad to raise a federal statute as a defense, there was no federal question jurisdiction: the federal issue wasn't part of their actual claim. On exams, watch for plaintiffs who try to smuggle a federal issue in by predicting the defendant's defense.

Under 28 U.S.C. § 1332, federal courts can hear cases between citizens of different states (or between a citizen and a foreign party) when the amount in controversy exceeds $75,000. Diversity jurisdiction exists to protect out-of-state parties from potential local bias.

Two requirements must both be met. First, complete diversity: under Strawbridge v. Curtiss, no plaintiff may share state citizenship with any defendant. If even one plaintiff and one defendant are co-citizens, complete diversity is destroyed.

Second, the amount in controversy must exceed $75,000 — meaning more than that figure, not exactly that figure. Courts generally accept the plaintiff's good-faith allegation of the amount unless it appears to a legal certainty that the claim is for less.

Diversity turns on citizenship, which is defined differently for people and entities — a frequent source of errors.

An individual is a citizen of the one state where they are domiciled: their true, fixed home where they intend to remain, which changes only by moving there with intent to stay. Mere residence isn't enough.

A corporation is a citizen of two places: its state of incorporation and the state of its principal place of business. Under Hertz Corp. v. Friend, the principal place of business is the corporation's "nerve center" — typically its headquarters, where the officers direct and control activities. (Unincorporated entities like partnerships and LLCs take the citizenship of all their members, which can quietly destroy diversity.)

Two related doctrines round out the picture. Supplemental jurisdiction (28 U.S.C. § 1367) lets a federal court hear additional state-law claims that are so related to the anchor claim that they form part of the same case or controversy — useful when a plaintiff has a federal claim plus related state claims.

Removal (28 U.S.C. § 1441) lets a defendant move a case from state court to federal court, but only if the federal court would have had original jurisdiction in the first place. There are limits — notably, a defendant generally can't remove a diversity case if sued in its own home state.

For a 1L exam, you usually only need to flag these and tie them back to the core question: is there an independent basis for federal subject-matter jurisdiction?

The most common error is blurring subject-matter jurisdiction with personal jurisdiction. Subject-matter jurisdiction asks whether the court can hear this kind of case; personal jurisdiction asks whether the court has power over this defendant. A case can satisfy one and fail the other.

A second frequent mistake is treating diversity citizenship like the personal-jurisdiction "at home" test. They overlap for corporations but answer different questions, and individuals are handled differently (domicile for diversity).

Finally, remember the procedural asymmetry: subject-matter jurisdiction can never be waived and can be raised at any time, while personal jurisdiction can be waived. If a defendant litigates for months and then challenges subject-matter jurisdiction, that challenge is still valid — and that's exactly the kind of fact pattern professors love.