MBE Rules · Civil Procedure
Supplemental jurisdiction
28 U.S.C. §1367
The rule
A federal court with original jurisdiction over a claim may exercise supplemental jurisdiction over related claims forming part of the same case or controversy (common nucleus). In DIVERSITY-ONLY cases, §1367(b) bars supplemental jurisdiction over plaintiffs' claims against parties joined under Rules 14, 19, 20, 24 if it would destroy complete diversity.
In plain English
If a federal court is handling a main case, it can also deal with related smaller claims if they're closely connected. But in diversity cases, it can't if the smaller claims mess up the needed diversity of parties.
Worked example
A buyer sues a seller in federal court for breach of contract. The buyer also wants to sue a supplier involved in the deal. If adding the supplier ruins the diversity of states, the court can't hear that claim.
Memory hook
Same Case, Same Court. Supplemental jurisdiction covers related claims sharing a common nucleus in federal cases.
The trap
Students think: Any related claim is covered. Wrong, because §1367(b) restricts in diversity-only cases. The actual test is if it destroys complete diversity.
How examiners test it
The MBE loves: diversity-only case, plaintiff adds claim against joined party. Trap: assuming it's allowed. Remember, §1367(b) bars if it destroys complete diversity.
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