International organizations' practice in the interpretation of their constituent instruments.

This article examines the role and legal significance of international organizations' practice in interpreting their constituent instruments under the Vienna Convention on the Law of Treaties (VCLT). While established or unanimously consented practices by States parties are recognized as authoritative interpretations under Articles 5 and 31(3) of the VCLT, the status of other organizational practices remains unclear. The article argues that earlier practices of international organizations can be considered credible evidence of the original intention of States parties and thus be taken into account under Article 31 of the VCLT, using the likelihood ratio from probability theory to assess their probative value. Practices not consented to by all States or not established may be better treated as supplementary means of interpretation under Article 32. This approach seeks to reconcile judicial practice and legal theory by grounding the consideration of organizational practice in the inference of States parties' original intent, while acknowledging challenges in evaluating such evidence.