“If I should call a sheep’s tail a leg, how many legs would it have? Four, because calling a tail a leg would not make it so.” This old quip, often attributed to Abraham Lincoln, captures an issue at the heart of the modern law of subject matter jurisdiction. Some believe that there is a Platonic ideal of jurisdiction that cannot be changed by judicial or legislative fiat. Others take a positivist approach and assert that jurisdiction is nothing more than whatever a legislature says it is. Who is right?
Neither and both. Although neither idealism nor positivism is the best approach, a combination of both is. The law of jurisdiction in the United States, like all positive law, is a human creation and thus susceptible to modification by humans. If lawmakers want their jurisdictional sheep to have five legs, they are free to declare the tail a leg, and courts must heed that declaration. But lawmakers occasionally speak ambiguously. When courts encounter ambiguity—like a tail that may or may not be a leg—they should resolve the ambiguity in a way that affirms, rather than contradicts, the ideal.