The question that has been put to us is: "What use is modern positivism?" In the following remarks, I would like to use the approach which I regard as the most fitting among the "modern" positivists--Hans Kelsen's Pure Theory of Law--and discuss its methodological commitments as relating to the use of positivism. Then I would like to "test" Kelsen on a point where his positivism might be weakest. Surely Kelsen cannot explain the "nonpositive" general principles of law? It might seem paradoxical, but it is precisely here where the particular strengths of his modern positivism shine, particularly as against "old school" voluntarism.
INTRODUCTION: WHAT USE IS MODERN POSITIVISM?
My answer to the question of the use of a legal-theoretical approach will not elicit an answer in the two most common forms found in international legal scholarship. First, as a legal scholar I am not enamored of the quest for global justice. I do not think that it is particularly helpful to rate legal theories according to how far they go in helping to bring about certain outcomes a particular ideology may require. Second, I also do not think that it is easy to rank legal theories with respect to their explanatory powers. It is not unproblematic to rank approaches in empirical sciences according to how much of our world they explain, and it is illusory to think that non-empirical theories can be ranked thus. In one of Alfred Verdross's papers, he proposed a multiplicity of custom-creative processes to be applicable to international law. He simply accepted all procedures that usually succeed in creating customary international law. (1) The gist of this example is: theories that can explain the coming about of more customary norms than another are better. It also shows the limits of that approach, because this means begging the question. How can we find out what "process" usually creates customary international law, if we do not know when law has validly been created in the first place? This requires knowing the meta-norm of customary international law creation, which he sets out to find.
Kelsen's "use" for international legal scholarship is different. It lies in the specifically legal approach which alone succeeds in not admixing the legal with the political, moral, or empirical viewpoint. His is a radical program of re-imagining the theoretical and epistemological basis of legal scholarship. The two most important and fundamental elements of this approach are the purity of legal science and the fundamental Is-Ought duality.
(1) Hans Kelsen wanted to found a science of law and to purify that scholarly enterprise. Legal science should be kept free from all those elements foreign to the specific methods of a science whose only purpose is the cognition of law. It may sound frivolous to insist on sticking to the legal method in an age such as ours, where holism and the admixture, willy-nilly, of methods is praised and sometimes even required by one's peers. But Kelsen's own age was not that different from ours, and the problems that ensue from methodical syncretism are timeless. Sure, Kelsen says, we can conduct sociological studies into whether the law is generally obeyed or not; this is a very valuable field of study. But sociologists or other empirical studies can only capture the periphery, not the norms themselves. Moreover, if legal scholars admix sociological findings with the normativist approach, they risk falsifying the results of their work. The UN Charter does not change because and when the political constellations change--a scholar claiming that does not accurately portray the law. Imagine, by way of contrast, a zoologist who admixes normative aesthetics and zoology to claim that a neon-pink butterfly exists because it would be beauty in perfection.
(2) Kelsen was one of the staunchest advocates of a categorical distinction between what is and what ought to be--whether that Ought is formulated in a law, morals, or unconnected to a major normative order. …