Customary international law, Congress and the courts: origins of the later-in-time rule

Abstract

This essay examines the origins of the later-in-time rule with respect to customary international law. It shows how seemingly contradictory statements in the early cases about whether statutes could supersede the law of nations as a rule of decision are largely explained by the existence in the late eighteenth century of more than one category of unwritten international law. Vattel’s Law of Nations recognized a “voluntary law of nations” based on natural law from which nations could not depart and a “customary law of nations” based on state practice from which they could. The essay goes on to sketch three shifts in the American understanding of the law of nations during the nineteenth century: (1) the shift from natural law to positivism; (2) the shift from individual consent to general consent; and (3) the shift from monism to dualism. All these changes were reflected in the Supreme Court’s Paquete Habana decision at the turn of the twentieth century. And these changes, in combination with The Paquete Habana’s “controlling...legislative act” dictum set the stage for the adoption of the later-in-time rule during the twentieth century.