⚡ 10-Second Rule
A claim with no federal ticket of its own can ride into federal court with a related claim that has one.
🧒 ELI-10 Scene
Zoe buys a ticket to the dinosaur museum. Her ticket covers the main hall. It also lets her into the small fossil room attached to the same hall — same building, same story, one visit. The guard, Mr. Okafor, allows it because the rooms belong together. But Zoe can't use the fossil room's side door to sneak in her cousin Theo. Theo was turned away at the front desk, and a side door can't undo the front-desk rules. And if the main hall closes early, Mr. Okafor can send everyone out of the fossil room too.
⚖️ Actual Rule
28 U.S.C. § 1367(a) provides that, except as limited by subsections (b) and (c), "in any civil action of which the district courts have original jurisdiction, the district courts shall have supplemental jurisdiction over all other claims that are so related to claims in the action within such original jurisdiction that they form part of the same case or controversy under Article III of the United States Constitution," including "claims that involve the joinder or intervention of additional parties." Claims satisfy this test when they share a common nucleus of operative fact with the anchor claim. United Mine Workers v. Gibbs, 383 U.S. 715 (1966). Section 1367(b) carves back: in cases founded solely on diversity, there is no supplemental jurisdiction over claims by plaintiffs against persons made parties under Rule 14, 19, 20, or 24, or over claims by persons proposed to be joined as plaintiffs under Rule 19 or seeking to intervene as plaintiffs under Rule 24, when exercising jurisdiction would be inconsistent with § 1332's requirements. A jurisdictionally sufficient plaintiff's claim can, however, anchor a co-plaintiff's related claim that fails only the amount in controversy — though never one that destroys complete diversity. Exxon Mobil Corp. v. Allapattah Services, Inc., 545 U.S. 546 (2005). Under § 1367(c), the court may decline supplemental jurisdiction if the claim "raises a novel or complex issue of State law," if it "substantially predominates" over the anchor claims, if "the district court has dismissed all claims over which it has original jurisdiction," or "in exceptional circumstances" for "other compelling reasons."
ELI-10 translation: related claims from the same real-world story ride along, but plaintiffs can't use the ride to dodge the diversity rules.
🔍 Ask These Questions
- Is there an anchor claim with its own federal question or diversity jurisdiction? (Someone must hold a real ticket first.)
- Does the add-on claim share a common nucleus of operative fact with the anchor? (Do both claims grow from the same real-world story?)
- Is the anchor diversity-only? If not, § 1367(b) never applies. (The side-door ban only guards the diversity entrance.)
- If diversity-only, is the add-on a claim by a plaintiff against a party joined under Rule 14, 19, 20, or 24? (Plaintiffs can't sneak in claims the front desk already refused.)
- Would allowing it be inconsistent with § 1332 — destroying diversity, or an amount shortfall the Exxon rule doesn't forgive? (Would the ride-along break the very rules it skipped?)
- Even if jurisdiction exists, might the court decline under § 1367(c) — novel state issue, state claim dominates, anchor dismissed, or exceptional reasons? (The guard can still say no, especially once the main hall closes.)
⚠️ Bar Trap
Exam language: Examiners build a diversity-only suit, have the defendant implead a third party under Rule 14, then have the plaintiff assert a related claim against that non-diverse third-party defendant — and offer "same case or controversy" as the ticket in. Section 1367(b) withholds supplemental jurisdiction from that plaintiff's claim. The mirror trap runs the other way: the same bar does not reach the defendant's or third-party defendant's own related claims, and students wrongly exclude those too.
ELI-10: The ban is a one-way gate aimed at plaintiffs in diversity cases. Related claims by defendants still ride along fine.
🧪 Question
A cyclist, a citizen of California, sued a charter bus company, a citizen of Nevada, in federal district court for $300,000 in negligence damages arising from a highway collision. The bus company impleaded its brake mechanic, a citizen of California, under Rule 14, alleging the mechanic must indemnify it for any liability from the collision. The cyclist then amended her complaint to assert a negligence claim directly against the mechanic based on the same collision. The mechanic moves to dismiss the cyclist's claim against him for lack of subject matter jurisdiction.
Should the court grant the motion?
(A) No, because the cyclist's claim against the mechanic arises from the same common nucleus of operative fact as the anchor claim. (B) No, because § 1367(a) expressly extends supplemental jurisdiction to claims involving joinder of additional parties. (C) Yes, because § 1367(b) withholds supplemental jurisdiction over a plaintiff's claim against a party impleaded under Rule 14 where the parties are not diverse. (D) Yes, because federal courts may never adjudicate a state-law claim between two citizens of the same state.
Answer: (C). The action rests solely on diversity, the mechanic was made a party under Rule 14, and the cyclist — a plaintiff — asserts a claim against him that would be inconsistent with § 1332, since both are Californians. Section 1367(b) strips the supplemental jurisdiction that § 1367(a) would otherwise supply.
💡 Why the Wrong Answers Are Wrong
- (A) stops at § 1367(a); the common-nucleus test is necessary but not sufficient, because § 1367(b) then subtracts this exact claim.
- (B) quotes the right statute and misses its carve-out; the joinder language in subsection (a) is expressly subject to subsection (b).
- (D) proves too much; such claims are heard routinely under supplemental jurisdiction — for example, this same claim brought by the bus company.
- ELI-10: The misconception is stopping after "same story, rides along." There's a second checkpoint that blocks plaintiffs from dodging the diversity rules.
