Since Article 38 of the Statute of the International Court of Justice
in 1945 incorporated international customs into the sources of international
law, how to accurately define the two constituent elements of customary
international law: national customs (material factors) and legal beliefs
(psychological factors) has become an important issue. Another unresolved
issue of international law. Two traditional identification methods: strict
induction and flexible deduction have played an important role in the judicial
practice of the International Court of Justice. The same two identification
methods also reflect different ways of identifying customary international law.