When interpreting international public law, consult Article 38(1) of the Statute of the International Court of Justice for sources of of international law:
- The Court, whose function is to decide in accordance with international law such disputes as are submitted to it, shall apply:
- international conventions, whether general or particular, establishing rules expressly recognized by the contesting states;
- international custom, as evidence of a general practice accepted as law;
- the general principles of law recognized by civilized nations;
- 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.
In international sales law, however, governed by the Convention on International Sale of Goods, it is Article 7 of the CISG that provides the standards for the interpretation:
- In the interpretation of this Convention, regard is to be had to its international character and to the need to promote uniformity in its application and the observance of good faith in international trade.
- Questions concerning matters governed by this Convention which are not expressly settled in it are to be settled in conformity with the general principles on which it is based or, in the absence of such principles, in conformity with the law applicable by virtue of the rules of private international law.
It depends on whether researching international public, international private, or foreign law to identify and locate sources of law, which may include any of the following:
- Treaties (= bilateral or multilateral international conventions) establishing rules expressly recognized by the contesting states (general or particular).
- Customary International Law (= custom) as evidence of general practice accepted as law (determined by majority of affected states). Custom will amount to a new rule when it is evidenced by practice and recognition by States amounting to a binding international obligation (= opinio juris).
- General Principles of Law recognized by 'civilized' nations
- Jus cogens (= peremptory norms) as defined by Article 53 of the Vienna Convention on the Law of Treaties 1969 are norms accepted and recognized by the international community of States as a whole as a norm from which no derogation is permitted and which can be modified only by a subsequent norm of general international law having the same character.
- Travaux Préparatoires = [French 'preparatory work'] Materials used in preparing the ultimate form of an agreement or statute, and especially of international treaty; the draft or legislative history of a treaty. If treaty interpretation is at issue, travaux provide insight into the intent of drafters.
- Teachings of the most highly qualified publicistis and scholars of various nations - writings and publications of scholars have influence on the international courts.
- Judicial Decisions (= judgments of courts and tribunals) are considered subsidiary sources of international law. N.B. Notice advisory opinions issued by international courts and tribunals when interpreting and understanding the substance and application of international law.
- Soft Law, the official existence of which is disputed by many, would include instruments of suggestion and recommendation, including guidelines, principles, declarations, codes of practice, programmes, etc.
- Comity are not legally binding rules of traditional practice of goodwill, politeness or convenience. It is based on the principle of reciprocity and it may eventually grow into a binding rule.