In some instances, the primary sources of international law (conventions, custom, general principles) are silent on specific issues, elements or factors. In these cases, courts rely on other judicial decisions and scholarly writings to guide their decisions. International courts treat theories under this category as persuasive evidence of authority, meaning they weigh the theory with any other support found from other sources of law. Article 38 of the ICJ Statute External describes this source as "judicial decisions and teachings of the most highly qualified publicists of the various nations . . ."
Section 103 of the Restatement Third provides, in part:
(2) In determining whether a rule has become international law, substantial weight is accorded to:
(a) judgments and opinions of international judicial and arbitral tribunals;
(b) judgments and opinions of national judicial tribunals;
(c) the writings of scholars;
(d) pronouncements by states that undertake to state a rule of international law, when such pronouncements are not seriously challenged by other states.