This chapter argues that the most relevant of Hart’s insights for contemporary international legal scholarship are to be found in his reductionism. It contends that the Hartian concept of law is germane to the extent that it helps international legal scholars to restrict international legal positivism to a mechanism for determining the mode of existence of norms; that is, their validity. Hart’s positivism is reductionist in that it confines legal positivism to a theory about the determination of the existence of law by virtue of a theory of sources, i.e. a theory of the ascertainment of rules. In that sense, Hart’s theory renders legal positivism a tool of limited scope which does not lay down a grand theory of law, and which is certainly not a content-determining mechanism.
According to this view, Hart’s Concept of Law is alien to the search for legal certainty and immanent truth as regards the content of law. This is why it is argued here that, from a Hartian perspective, international legal positivism is not about determining the right content of norms and the right adjudicative truth. Instead, international legal positivism should be confined to a thesis about the validity-condition of legal norms.
The Hart-inspired international legal positivism which is put forward here is premised on the idea that international legal positivism is deficient when it comes to deciphering and unraveling the other dimensions of international law such as the creation of subjects, the description of the multi-dimensional phenomenon of law-making or the compliance pull of international legal rules to name only a few. This understanding of international legal positivism simultaneously brings with it a division of tasks among various approaches to international law within international legal scholarship, each of them recognised as having distinct merits that can be mutually reinforcing.