International, Foreign, and Comparative Law: Custom & Principles

Article 38(1) of the Statute of the International Court of Justice includes:

b. international custom, as evidence of a general practice accepted as law;

c. the general principles of law recognized by civilized nations;

Restatement (Third) of Foreign Relations Law § 102 (1987) notes that "Customary international law results from a general and consistent practice of states followed by them from a sense of legal obligation."

The Restatement further explains, “'Practice of states,' . . . includes diplomatic acts and instructions as well as public measures and other governmental acts and official statements of policy, whether they are unilateral or undertaken in cooperation with other states. . . Inaction may constitute state practice, as when a state acquiesces in acts of another state that affect its legal rights. The practice necessary to create customary law may be of comparatively short duration, but under Subsection (2) it must be “general and consistent.” A practice can be general even if it is not universally followed; there is no precise formula to indicate how widespread a practice must be, but it should reflect wide acceptance among the states particularly involved in the relevant activity. Failure of a significant number of important states to adopt a practice can prevent a principle from becoming general customary law though it might become “particular customary law” for the participating states."

Regarding principles, the Restatement notes, "It has become clear that this phrase refers to general principles of law common to the major legal systems of the world." The Restatement provides some examples or rules derived "from general principles," including "rules relating to the administration of justice, such as the rule that no one may be judge in his own cause; res judicata; and rules of fair procedure generally. General principles may also provide 'rules of reason' of a general character, such as acquiescence and estoppel, the principle that rights must not be abused, and the obligation to repair a wrong."