<Li> When the treaty rule reproduces an existing rule of customary law, the rule will be clarified in terms of the treaty provision . A notable example is the Vienna Convention on the Law of Treaties 1969, which was considered by the ICJ to be law even before it had been brought into force . </Li> <Li> When a customary rule is in the process of development, its incorporation in a multilateral treaty may have the effect of consolidating or crystallizing the law in the form of that rule . It is not always easy to identify when this occurs . Where the practice is less developed, the treaty provision may not be enough to crystallize the rule as part of customary international law . </Li> <Li> Even if the rule is new, the drafting of the treaty provision may be the impetus for its adoption in the practice of states, and it is the subsequent acceptance of the rule by states that renders it effective as part of customary law . If a broad definition is adopted of state practice, the making of a treaty would fall within the definition . Alternatively, it is possible to regard the treaty as the final act of state practice required to establish the rule in question, or as the necessary articulation of the rule to give it the opinion juries of customary international law . </Li> <Li> Convention - based "instant custom" has been identified by the ICJ on several occasions as representing customary law without explanation of whether the provision in question was supported by state practice . This has happened with respect to a number of provisions of the Vienna Convention on the Law of Treaties 1969 . If "instant custom" is valid as law, it could deny to third parties the normal consequences of non-accession to the </Li>

Difference between general principles of law and customary international law