4. Customary international law.

The Statute of the International Court of Justice lists, among the sources of public international law, 'international custom, as evidence of a general practice accepted as law'1. This refers to customary international law2. Customary international law is to be distinguished from mere usage, in that it arises from state practice accompanied by acceptance as law (opinio juris), that is, a conviction on the part of the states in question that it is required by international law or is regulated by or in conformity with international law