What must be proven for supplemental jurisdiction to apply under § 1367(b)?

For supplemental jurisdiction to apply under § 1367(b), it must be shown that the claims derive from a common nucleus of operative fact. This means that the additional claims are related to the original claims in such a way that they share essential facts and circumstances. This connection allows the court to consider the related claims together, thus promoting judicial efficiency and consistency in the outcomes of cases.

The focus on a common nucleus of operative fact serves to maintain the integrity of the original jurisdiction, ensuring that related claims are adjudicated in conjunction with one another. This principle enables courts to handle not only the primary federal question but also the related state law claims, as long as they arise from the same incident or set of facts.

By allowing for the joinder of related claims under supplemental jurisdiction, courts can avoid multiple lawsuits that could lead to inconsistent judgments, enhancing the overall efficiency of the judicial process. This principle is foundational to the concept of supplemental jurisdiction, reinforcing the connection between various claims and preventing fragmentation of litigation.