The question of ‘might versus right’, as to whether might makes right or is subject to it, is one of the overarching questions of Western moral and political thought from the ancient Greeks to today. This is an exploration of that question, the debate between the proponents of might (‘Realists’), the proponents of right (‘Idealists’), and the opponents of both (‘Relativists’). It is particularly concerned with the sources of this debate, in the founding figures of these schools of thought and the foundational thought of the tradition as a whole. This debate forms a dialectic that spans much of the history of Western ancient and modern moral and political philosophy, crossing over to a number of related fields. This study is therefore concerned with both the traditional spheres of moral and political philosophy (the theory of nature and the theory of law) and certain related fields (theology, mythology and metaphysics). It provides an overview of this dialectic, its sources, and the relationship between its theoretical and practical aspects.