Note on claim aggregation

Some general rules can be stated simply:

1. Separate plaintiffs may not aggregate the value of their claims to satisfy the jurisdictional amount.
2. A single plaintiff may aggregate claims against a single defendant to satisfy the jurisdictional amount, even if the claims are entirely independent.
3. A single plaintiff may not aggregate claims aganinst multiple defendants to satisfy the jurisdictional amount.

Uncertainty exists with respect to whether supplemental jurisdiction may extend, under section 1367, to claims that are not within the subject matter jurisdiction of federal courts under these rules. For example, suppose P1 has a claim against diverse D for $80,000. P2, also diverse from D, joins a claim for $25,000 against the same defendant, under Rule 20. Number 1 above says that there is no diversity jurisdiction over P2's claim. But section 1367(a) could be read to extend supplementatal jurisdiction over P2's claim if the two claims share a common nucleus of operative fact.

Courts and commentators disagree on whether this is a permissible interpretation of 1367, with the majority appearing to prefer a negative answer. In any event, one must be attentive to the language of 1367(b), which limits supplemental jurisdiction over additional claims filed by the original plaintiff. See annotation notes 52 and 53 to 28 U.S.C.A. sec. 1367.

Given the uncertainty about interpretation, you should be able to make textual and policy arguments on both sides of the issue.