INTRODUCTION

What if a treaty rule and a customary norm coexist or conflict? Which should have precedence? How should any conflicts be resolved?

Article 38 of the Statute of the International Court of Justice (ICJ) does not indicate how the different sources of international law are to be reconciled and does not assign any one source priority. Early drafts of the provision would have required that the sources be applied in the listed order – first treaties if applicable, then customary law, and finally general principles of law if necessary to prevent a “non-liquet” – but this requirement was eventually dropped. The approach developed here helps provide some answers. These are largely consistent with traditional doctrine, but also expand upon it in particular ways.

A CASE OF NO CONFLICT

Let us first take the case of a treaty rule and a customary norm that coexist but are not in direct conflict. In this case it would seem desirable to respect both norms to the extent possible as expressions of the will of states in the global community of states. A careful analysis is required as to whether there is in fact a necessary conflict between a treaty rule and a customary norm.

In a number of cases courts have determined that there is no such conflict. For example, in the 2002 Arrest Warrant Case, the ICJ considered whether treaties that extended the criminal jurisdiction of national courts to try persons suspected of having committed serious crimes, including Ministers of Foreign Affairs, conflicted with a customary rule granting these officials diplomatic immunity from criminal prosecution.