When does diversity jurisdiction become relevant in supplemental jurisdiction cases?

Diversity jurisdiction is a specific type of subject matter jurisdiction that allows federal courts to hear certain cases involving parties from different states, provided that the amount in controversy exceeds a specified threshold. In the context of supplemental jurisdiction, which allows a federal court to hear additional claims that are related to the claims over which it has original jurisdiction, diversity jurisdiction primarily comes into play when it is the sole basis for legal action.

The relevance of diversity jurisdiction in supplemental jurisdiction cases becomes particularly important when a plaintiff aims to include additional claims against parties who may not meet the diversity criteria if the original claim was based on diversity alone. For example, if a plaintiff has an original diverse claim against one defendant and wishes to add another defendant from the same state as the plaintiff, supplemental jurisdiction may allow that addition only if there is an overarching original jurisdiction that still qualifies under diversity.

The other options do not accurately capture this concept. If all parties reside within the same state, diversity jurisdiction would not apply at all. The notion that the amount in controversy is exceeded by the claims is not directly related to the mechanics of supplemental jurisdiction. Similarly, while a claim can indeed be brought against a third-party defendant, that act does not in itself invoke diversity jurisdiction unless the jurisdictional criteria of diversity are