In his 2015 book, Key Concepts in Politics and International Relations, Andrew Heywood wrote:
International law is an unusual phenomenon. As traditionally understood, law consists of a set of compulsory and enforceable enforceable rules, reflecting the will of a sovereign power. And yet no central authority exists in international politics that is capable of enforcing rules, legal or otherwise. International law is therefore ‘soft’ rather than ‘hard’ law. Some, as a result, dismiss the idea of international law as nothing more than a collection of moral principles and ideals.
