Sources of International Law

Sources of international law are the materials and processes out of which the rules and principles regulating the international community are developed. They have been influenced by a range of political and legal theories. During the 19th century, it was recognised by legal positivists that a sovereign could limit its authority to act by consenting to an agreement according to the principle pacta sunt servanda. This consensual view of international law was reflected in the 1920 Statute of the Permanent Court of International Justice, and preserved in Article 38(1) of the 1946 Statute of the International Court of Justice.

Article 38(1) is generally recognised as a definitive statement of the sources of international law. It requires the Court to apply, among other things, (a) international conventions "expressly recognized by the contesting states", and (b) "international custom, as evidence of a general practice accepted as law". To avoid the possibility of non liquet, sub-paragraph (c) added the requirement that the general principles applied by the Court were those that had been "the general principles of the law recognized by civilized nations". As it is states that by consent determine the content of international law, sub-paragraph (d) acknowledges that the Court is entitled to refer to "judicial decisions" and the most highly qualified juristic writings "as subsidiary means for the determination of rules of law".

On the question of preference between sources of international law, rules established by treaty will take preference if such an instrument exists. It is also argued however that international treaties and international custom are sources of international law of equal validity; this is that new custom may supersede older treaties and new treaties may override older custom. Certainly, judicial decisions and juristic writings are regarded as auxiliary sources of international law, whereas it is unclear whether the general principles of law recognized by 'civilized nations' should be recognized as a principal or auxiliary source of international law.

It may be argued that the practice of international organizations, most notably that of the United Nations, as it appears in the resolutions of the Security Council and the General Assembly, are an additional source of international law, even though it is not mentioned as such in Article 38(1) of the 1946 Statute of the International Court of Justice. Article 38(1) is closely based on the corresponding provision of the 1920 Statute of the Permanent Court of International Justice, thus predating the role that international organizations have come to play in the international plane. That is, the provision of Article 38(1) may be regarded as dated, and this can most vividly be seen in the mention made to 'civilized nations', a mentioning that appears all the more quaint after the decolonization process that took place in the early 1960s and the participation of nearly all nations of the world in the United Nations.

It is also possible, though less common, for a treaty to be modified by practices arising between the parties to that treaty. The other situation in which a rule would take precedence over a treaty provision would be where the rule has the special status of being part of the jus cogens.