ABSTRACT
The attitude of international lawyers towards customary international law is somewhat similar; they invoke rules of customary international law every day, but they have great difficulty in agreeing on a definition of customary international law. This chapter deals with the relationship between treaties and custom. In the North Sea Continental Shelf cases the International Court treated the Truman Proclamation and similar claims by other States as State practice which had given rise to a rule of customary law. Anthony D'Amato argues that claims and other statements by States are likely to conflict with one another, and that physical acts do not suffer from this defect. Assertions made in abstracto concerning the content of existing law are sometimes found in resolutions passed by the representatives of States at the meetings of international organizations. In the Nottebokm case the International Court relied partly on the fact that national laws provide for naturalization only when there is a genuine link.
