Due diligence as a secondary rule of general international law

Abstract The conventional understanding of due diligence in international law appears to be that it is a concept that forms part of primary rules. During the preparatory stages in creating the Articles on Responsibility of States for Internationally Wrongful Acts (ARSIWA), the International Law Commission (ILC) focused on due diligence as though it could have formed part of secondary rules. Despite this process, no due diligence provision forms part of the ARSIWA. Yet a number of the final provisions are based on primary rules. This is because the ILC relied on the method of extrapolation in attempts to create secondary rules. Extrapolation is a method of international law-making by which the output of an analytical process is reproduced in a different form following an examination of its content that exists in other forms. In using this method, the ILC attempted to create secondary rules by extrapolating from primary rules. Yet it did not do so with respect to due diligence. However, due diligence can be formulated and applied differently by using this same method. This article analyses the steps of this process to construct a vision of where international legal practice should venture in the future. In learning from and amalgamating the dominant trends in different areas of international and domestic law, this article proposes that due diligence could exist as a secondary rule of general international law. By formulating and applying due diligence as a secondary rule, there is potential to develop the general international law applicable to determining state responsibility for the conduct of non-state actors.