The conduct of international affairs is subject to three kinds of normative standards. The first of these is prudence or rational self-interest, and its most common manifestation in international affairs involves reference to a state's national interest as a basis for defending or critiquing its international conduct. Justice provides a second metric for assessing the international conduct of states, and sometimes other actors, and a set of normative concepts including freedom, equality and fairness with which to argue for or against particular acts or policies. Law, including both international law and the foreign law of particular states, provides the third normative framework commonly employed by those engaged in or otherwise concerned with international affairs. Thus an international act, such as one state's invasion of another, can be criticized as imprudent, and/or as unjust and/or as illegal. As normative claims, each of these criticisms purports to give the invading state a reason to desist, and at least in the case of the second and third criticisms, entails that the invaded state and perhaps other actors (for example, other states) have a reason to treat the invading state in ways they would not otherwise be justified in doing. The focus of this chapter is on how international law performs this function; that is, it aims to explain why and when the fact that an act would violate international law in itself provides an actor with a reason, indeed a moral obligation, not to perform it. The answer, I shall argue, is that international law does so if and only if it is legitimate.

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© 2016, Cambridge. This material has been published in Global Political Theory, David Held and Pietro Maffettone (eds.). (Cambridge, UK: Polity, 2016): 98-116. This version is free to view and download for private research and study only. Not for re-distribution or re-use.

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The definitive version is available at: https://www.wiley.com/en-us/Global+Political+Theory-p-9780745685182