Recent Development in ICJ's Jurisprudence on the Indentification of Customary Law

Customary law is one of the main sources of international law, but its identification remains complex. Over the years, doctrine and jurisprudence have tried to solve problems concerning the assessment of its constitutive elements, the process of its birth, the methodology for the deduction of its existence. A recent ICJ’s judgment, in a dispute between Nicaragua and Colombia, reopened a debate on these issues. As concerns opinio iuris, the Court stated that it can be inferred from a constant and uniform practice and that it is met even if States’s behaviour was justified by extra-juridical reasons. With regard to practice, the Court only considered a part of it, omitting to take into account States’ behaviour in a variety of situations and occasion and, moreover, failing to prove States’s abstention was carried out with a sense of legal obligation. For these reasons, the judgment challenged many aspects regarding the assessment of practice and opinio iuris, as well as the methodology to deduce the existence of a custom, contrasting with its previous jurisprudence and the main doctrine on the matter.