14/08/2019
The Sources of International Law
There are four sources of the rules of international law. The first is treaty, which is analogous to the domestic law notion of contract. The word "treaty" in international law includes all the many different sorts of international instruments intended to create binding obligations, whether the particular instrument is labeled an "agreement," "convention," "accord," etc. (In U.S. domestic law, the word "treaty" refers only to those international agreements that are approved by two-thirds of the Senate, as discussed below). International lawyers use the phrase pacta sunt servanda to express the fundamental principle that agreements between states must be complied with. The Statute of the International Court of Justice places "international conventions, whether general or particular, establishing rules expressly recognized by the contesting states," first in its list of the rules to be applied by the Court in deciding cases before it, and most commentators assign treaties the highest rank among the sources of international law.
A second source of international law is known as "custom." "Customary International Law" constitutes a widespread practice of states followed out of a sense of legal obligation. It is analogous to the domestic commercial law notions of "course of dealing" and "the usage of trade," where practice creates justifiable expectations of future observance. Like treaty law, customary international law reflects the consent of States. A State which persistently objects during the formation of a norm of customary international law is not bound by it.
A third source of international law is the general municipal practice of states. The idea behind these so-called "General Principles of Law" is that if most domestic legal systems recognize certain rules, then it may be presumed that these rules are so fundamental as to be a part of international law. General Principles of Law are often used as a gap-filler, where treaty and customary international law are silent. General Principles of Law recognized by the International Court of Justice, for example, include the principle of estoppel, the concept of unclean hands, the rule that every violation involves an obligation to make reparation, the principle of res judicata, the principle of equity and unjust enrichment, and the use of circumstantial evidence.2
Where the first three sources of international law may be said to emanate from the consent of states, the fourth source, known as "jus cogens," reflects the natural law concept of fundamental rights. Jus cogens limits the contractual power of parties to a treaty in much the way domestic contracts are void if they are found to contravene "public policy." The notion of jus cogens may, for example, be applied to invalidate treaties, customary international law, or domestic statutes which promote the use of aggression, slavery, genocide, or war crimes. In the 1992 Siderman case, the U.S. Ninth Circuit ruled that "the right to be free from official torture is fundamental and universal, a right deserving of the highest status under international law, a norm of jus cogens."3 The Court distinguished customary international law and jus cogens as follows: "Whereas customary international law derives solely from the consent of states, the fundamental and universal norms constituting jus cogens transcend such consent, as exemplified by the theories underlying the judgments of the Nuremberg tribunals following World War II."4
