Material Sources of International Law

Sources of international law can be defined as the actual ingredients from which a legal expert determines the rule of law that applies to certain circumstances. These materials are included in five main categories or forms, namely:
1. Habits
2. Treaties
3. Court decisions or arbitration tribunals
4. Legal works
5. Decisions or determinations of organs of international institutions.

From a practical point of view, we can imagine a legal advisor at a Ministry of Foreign Affairs who is asked to provide opinions on international law relating to certain issues. His job was not at all like the work of a practicing lawyer who only had to do with national law. He does not have a Code, there is no statutory statute, and often he is in an uncertain environment either because of uncertainty about whether there has been a customary rule of international law or because of the absence of customs or practices and opinions that guide him to find the right way out. However, he must explore the law between these material "sources", assisted by his own logic and reasoning ability and sense of justice.
It can be seen that this practical approach has been taken by the courts which have decided on international legal issues. According to Article 38 (1) of the Court Statute, the International Court of Justice is ordered to apply the following sources:
1. International treaties
2. International customs, as evidenced by common practice, have been accepted as law
3. General principles of law recognized by civilized nations
4. Judicial decisions and the teachings of prominent scholars from various countries as an additional source for establishing rules of law.

The order of material in the articles of the Statute does not cover decisions of arbitral tribunals concerning legal matters, or decisions or stipulations of organs of international institutions, even though the article includes one material "general principles of law recognized by civilized nations ". These general principles of law were incorporated into the Court Statute to provide an additional basis for decisions in the event that other materials cannot help the Court. These "general principles" must be used in analogy and can be drawn by selecting concepts recognized by all national legal systems. That is the original purpose of the compilers of the Statute, which was emphasized in the context of Article 9, according to which the elected judges must remember that the Court must represent "the main forms of civilization and the main legal systems in the world", and the efforts made by several authors to give another interpretation of these words seems artificial and inconclusive. The legal propositions quoted and widely popularized do not in themselves constitute "general principles" in this sense. The revised edition of the American Law Institute's Restament of the Foreign Relations Law of the United States (1986) classifies "general principles" as an "additional source of international law".
On several occasions the Permanent Court of International Justice considers it necessary to apply or refer to such "general principles". Therefore in the Chrozow Factory (Indemnity) Case, the Permanent Court of International Justice applies the principle of res judicata and refers to the "general conception of law", that "every violation of an agreement issues an obligation to compensate". In the Mavrommatis Palestine Concessions Case. The Court referred to "general principles of subrogation", and in Case of the Diversion of Water from the Meuse, Judge Manly O. Hudson expressly argued that the Court could apply the Anglo-American doctrine of merit as "general principles". But at least on one occasion, the Court refused to apply what was considered "general principles" namely in the Serbian Loans Case where the Court stated that the principle known in English law as "estoppel" (detention of someone to prevent it from denying the previous statement) cannot be applied. On the other hand, the doctrine of civil law regarding trust is considered beneficial in relation to issues concerning the Mandate system and the Trusteeship system. "General principles" include procedures and principles of clarity (evidentiary), as well as the principles of substantive law, provided that these principles have some general characteristics in the context of certain legal systems that are generally owned. However, these "general principles" constitute a weak "source" of international law compared to a matter of judicial reasoning and logic which today is specifically prohibited from being used by the most influential international courts.
From a theoretical point of view, the provisions for applying "general principles" have been echoed as "sounding the death knell" for positivism, because they explicitly reject the positivist's broad view that the habits and treaties must be viewed as sources exclusive of international law. The provision was also stated to solve the problem of non-liquet, namely the inability of an international court to decide a case legally because it could not find a rule of law that could be applied. Finally, this provision is almost regarded as a provision that does not stipulate a new rule, except as something that is stated in nature regarding the practice of international courts that have lasted a long time.