s.IV Treaty Interpretation, 19 The Vienna Convention Rules on Treaty Interpretation

Recourse may be had to supplementary means of interpretation, including the preparatory work of the treaty and the circumstances of its conclusion, in order to confirm the meaning resulting from the application of article 31, or to determine the meaning when the interpretation according to article 31:The idea that there are rules applicable to interpretation of all treaties is one that in past times would have been controversial, or at best uncertain as regards the content of any such rules. Now, however, the rules in the Vienna Convention on the Law of Treaties...