Sources of International Law: Treaties, Custom, and General Principles
General Principles of Law
This expression, used in the strict sense, refers to principles common to the legal systems of various states. Some are adaptable to the needs of the international legal order. Among these general principles of law, we can mention pacta sunt servanda (agreements must be kept). Another general principle of law is that no one can transfer more rights than they possess. Additionally, unlawfully caused harm should be fully repaired, and nobody can benefit from their own misconduct.
These general principles of law are reminiscent of the Roman Ius Gentium, consistent principles applied between peoples and within a common civilization. Arbitral tribunals have recognized general principles of law. The Statute of the Permanent Court of International Justice (the predecessor to the International Court of Justice) states in Article 38 that the court applies general principles of law recognized by civilized nations. This article confirmed a previous practice of resolving disputes in this way.
We also study the principles applied in deciding transnational disputes. These disputes arise from agreements and contracts between a government and a foreign company, with no intention of subjecting them to a particular national law.
General Principles of Law Applied to International Law
Within the rubric of general principles of law, we can also include some basic principles inherent in international law or basic assumptions of its rules. These general principles of international law include:
- Treaties prevail over domestic law at the international level.
- A state or government cannot invoke its domestic law as a basis or excuse for not complying with its international obligations.
- A change of regime, sovereign government, or even the sovereign, does not affect or alter the international obligations of a state or constitute a valid basis for noncompliance.
- Rebus sic stantibus, meaning “as long as conditions remain.”
- Pacta sunt servanda (agreements must be kept).
Jurisprudence
The jurisprudence of international tribunals has significantly influenced the development of international law and is the source of many of its standards. For example, the case of straight baselines arose from the ruling in the “Anglo-Norwegian Fisheries Case.” Decisions of these courts can be used as proof of customary international law and general principles of law. The merit of a given sentence, however, depends on several factors:
- The recognized authority of the court.
- The persuasive force of its arguments.
- The deserved welcome it receives from the legal community.
- The extent to which subsequent decisions have followed it.
The judgments of the International Court of Justice (ICJ) and its predecessor, the Permanent Court of International Justice, have far-reaching effects. Their relative effects can crystallize into formal standards of international law.
The Doctrine
Authors and writers do not create international legal standards. Their task is to determine, explain, and present the rules logically and systematically. They also have a role in critically analyzing existing law and proposing reforms. Therefore, the opinions of authors are not a formal source of international law. However, such opinions are cited to demonstrate or prove the existence, scope, or interpretation of a particular legal norm in the international arena.
In the formalist era of international law, much of this was part of general books on international law based on the views of renowned authors whose fundamental pieces were considered classics. In the absence of treaties and precedents, the authority of foreign ministries, and classic authors like Grostius, Suarez, and Vattel, were invoked. However, the practice of states, jurisprudence, and the publication of directories containing them have reduced the importance of doctrine as a means of determining the rules of international law.
Other Elements (Equity)
International courts also use other elements or aids in their decisions. These include treaties declaratory of international law, treaties and work presented by the International Law Commission, and UN resolutions on legal matters. Equity and natural reason are also incorporated to interpret and complement the content of positive international law rules.