“Green defends a ‘Kelsenian’ non-naturalist and non-reductive version of legal positivism that, he argues, is similar to the pure theory of law expressed in Hans Kelsen’s works. Kelsen is a peculiar legal positivist by Anglophone standards because he rejects the social thesis. As Kelsen sees it, law does not ultimately depend upon social facts about a community’s legal practices. The legal order is normative and so stands outside the spatiotemporal and causal world of nature. Nevertheless, Kelsen can be described as a positivist for two reasons. First, he accepts the separation thesis: law does not ultimately depend upon moral facts. Second, he accepts what Green calls the ‘positivity thesis’. Green argues that the heart of the Kelsenian argument against the social thesis is a form of legal anti-psychologism that is similar to the logical anti-psychologism offered by Frege. A challenge to this Kelsenian position is the view that the non-natural facts upon which legal inferences are based concern the concept of law, not a legal order. Green argues that this approach can be successfully resisted by invoking Kelsen’s doctrine of the unity of law.”