It is universally agreed that "usages generally accepted as expressing principles of law" constitute one of the main sources of international law. It is the purpose of this paper to investigate how a rule becomes "generally accepted" as a part of customary international law. There are several different ways in which international law deals with this subject. Ordinarily, a rule is considered generally accepted when it is supported by constant practice of states acting on the conviction that the practice is obligatory. Alternatively, an international agreement sometimes incorporates certain rules as ones considered to be generally accepted; or an agreement is considered as declaratory of certain generally accepted rules binding on all states. In addition, international agreements may also provide that rules to be adopted by an international organization shall be considered as generally accepted (unless a state expressly opts out). Occasionally, an international agreement that is not yet in force may become binding on all states because of its adoption by a consensus, signifying its general acceptance. Finally, a resolution of an international organization, adopted by consensus, or a nearly unanimous decision, may declare that a rule has become generally accepted.
Louis B. Sohn,
"Generally Accepted" International Rules,
61 Wash. L. Rev.
Available at: https://digitalcommons.law.uw.edu/wlr/vol61/iss3/15