Solidarity as a Practical Reason: Grounding the Authority of International Law

This article discusses the concept and the principle of solidarity in international law. It is often argued that solidarity is a(n) (emerging) principle of international law, yet its normative function in international law is not clear or well defined. I trace the development of the idea of solidarity and show how its image gradually shifted from reflecting the factual societal bonds to being mainly normative and thus functioning as a reason for action. In international legal scholarship, solidarity is often portrayed as a principle of international law, but there is a great deal of variety in which normative ideas we label as ‘principles’. There are several groups of ‘principles of international law’ that are very different in the type of the normative function they perform in or for international law. I investigate to which of these groups solidarity belongs and what can it tell us about its role in international law. I suggest that solidarity is a kind of normative principle, which, though essential for the legitimation of international law, is not legally normative by the function it performs. I draw a line between having a normative function within and outside the law, and use the concept of pre-emptive reasons to show why solidarity is not and should not be considered as a principle of international law in order to perform the normative function that it has. I argue that the authority of international law requires that normative ideals such as solidarity are pre-empted, and therefore replaced in practical reasoning, by legal rules.