A Practice Theory of International Law

Why should states follow international law? We are currently witnessing trends towards rapid expansion of international legal rules and a spreading presumption that treaties, custom, and other forms of law are binding for states. Despite this, work on the normative foundations of international law has not kept up. The predominant theories advanced in the contemporary literature focus on revising law to match some ideal set of criteria, rather than taking seriously the task of evaluating current regimes. Rather than ask what law should be, I ask: Is it possible to justify law as it is? In response, I investigate whether we can construct an independently attractive theory that can justify the authority of international law as we find it. My inquiry begins with an interpretive analysis of current practice, to identify both the form and scope of international legal authority. I then offer an analysis of current theories to see whether any can capture both aspects of current practice. While they cannot, this process gradually produces a silhouette of what a successful theory would have to look like. In light of this, I offer a positive answer to the question: the practice approach to international law. I propose that states have a duty to comply with international law because of the corrective function that system of rules fills in global politics