An important issue in American federalism has been the extent to which courts created by the federal government may adjudicate claims that would, standing alone, ordinarily lie outside their subject matter jurisdiction, but that have a relationship to matters already before the federal court.
The Demonstration explores this issue of "supplemental jurisdiction". You can vary: (1) the nature of the underlying jurisdiction-conferring claim; (2) the nature of the potential additional claim; and (3) the applicability of 28 U.S.C. § 1367, so as to appreciate how the enactment of that statute changed existing law.
Your selections yield a graphical illustration and a short description of the outcome. Federal jurisdiction exists over claims depicted with dark green arrows. Supplemental jurisdiction is available over claims depicted with light green arrows. No supplemental jurisdiction is available over claims depicted with red arrows. Yellow arrows denote a situation in which the existence of jurisdiction depends on additional factors.
Snapshot 1: A second plaintiff attempts, before the enactment of 28 U.S.C. § 1367, to add a non-federal claim against a defendant already defending a lawsuit with a claim that has an independent basis for federal jurisdiction.
Snapshot 2: A second plaintiff attempts, after the enactment of 28 U.S.C. § 1367, to add a non-federal claim against a defendant already defending a lawsuit with a claim that has an independent basis for federal jurisdiction.
Snapshot 3: A defendant attempts to bring a non-federal claim against a plaintiff that has sued the defendant on claim with an independent basis for federal jurisdiction.
Unless otherwise noted, the potential additional claims are assumed to be factually related to the underlying claim such that they form part of the same "case or controversy".
For all of the post-1367 results, bear in mind that the court may, in proper circumstances, choose to decline to exercise its supplemental jurisdiction. See § 1367(c). Similarly, under pre-1367 laws, courts had some discretion to decline jurisdiction over pendent claims and, to a lesser degree, ancillary claims. See United Mine Workers v. Gibbs, 383 U.S. 715 (1966) (pendent jurisdiction); Joiner v. Diamond M. Drilling Co., 677 F.2d 1035 Cir. 1982) (ancillary jurisdiction); Coleman v. Casey Bd. of Educ., 686 F.2d 428 Cir. 1982) (ancillary jurisdiction).