This Article will not seek to address all issues concerning the sources of customary international law; the subject is too vast for treatment at anything less than book length. Rather, this Article will focus on one category of possible sources--international treaties. Of course, if one considers treaties purely as treaties, they affect relationships between states parties to them, but treaties as treaties are not the subject here. Rather, the inquiry here is, since customary law depends on the practice of states, and because one form of practice in which states engage is entering into treaties, what weight should the legal community accord this particular form of state practice when determining the content of customary law? The importance of this question to the more general issue of the sources of customary law is, one hopes, obvious. Treaties, like statutes, are legal documents, more or less precisely phrased and accessible with relative ease. The more weight given to them in the determination of customary law rules, the easier it is to make such determinations. Conversely, if one considers treaties as merely one more form of state practice, one cannot answer questions as to the content of custom by looking solely at the text of relevant treaties; rather, it becomes necessary to undertake the difficult and confusing effort of figuring out what states are actually doing in the world.
Arthur M. Weisburd,
Customary International Law: The Problem of Treaties,
21 Vanderbilt Law Review
Available at: https://scholarship.law.vanderbilt.edu/vjtl/vol21/iss1/1