It is now some forty years since H. L. A. Hart famously made his careful delineation between law and morality. When he did so, it was not to denigrate the status of either, nor to elevate one over the other, but to draw attention to the different sense in which legal and moral rules can be said to be binding. So far as international law was concerned, Hart's reasoning marked an analytical break with a natural law tradition that had waxed and waned over the previous three centuries: at times in a jurisprudential effort to locate the binding origins of international law, and at other times in a more normative effort to isolate the content of the fundamental rules of international behaviour.

It is not the purpose of this essay to revisit that old issue, or to trace its recent recurrence in surprising new clothing. The paper adopts instead a different angle of approach, one which corresponds to the greater preoccupation latterly with the linked questions of compliance and enforcement, rather than with the ultimate origins of international law as such. In any society, the correlation between compliance and enforcement is fundamental to the functioning quality of its system of legal rules. Faced with the truism, however, that the international legal system lacks any general machinery to sanction breaches of its rules, the vital significance of patterns of voluntary compliance becomes immediately apparent.