Public International Law (Vol. I & II)
Article 38
The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall 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 the provisions of 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.
This provision shall not prejudice the power of the Court to decide a case ex aequo et bono if the parties agree thereto.