How do they fill gaps in international adjudication?

Article 38(1) of the ICJ Statute — the sources' canonical enumeration — directs the Court to apply: (a) international conventions, whether general or particular, establishing rules expressly recognized by the contesting states; (b) international custom, as evidence of a general practice accepted as law; (c) the general principles of law recognized by civilized nations; (d) subject to Article 59, judicial decisions and the teachings of the most highly qualified publicists of the various nations, as subsidiary means for the determination of rules of law.Two structural points: the list is not closed or hierarchical (Article 38 is a function description for the Court, not the system's exhaustive constitution — other formative sources exist below), and (d) sources are subsidiary — evidence and authentication of law, not law-makers.