The literature on the identification of rules of customary international law is extensive. Commentators have focused on isolating the methodologies by which international courts and tribunals identify customary international law, with most of the debate revolving around the use of induction, or deduction and assertion as methods of custom identification. However, the existing literature has overlooked that the choice among custom identification methodologies takes place behind closed doors, during confidential deliberation processes. When all that scholars see may be deduction or assertion, international courts and tribunals may have ascertained the existence of customary rules by induction, but induction may not have made it into the final text of the decision. This article elaborates on the impact of judicial deliberations at the International Court of Justice on the choice among custom identification methodologies. It argues that individual-driven stages of deliberations favour custom identification by induction, while collegial stages promote custom identification by non-inductive methodologies.
