Sieckmann argues that the central claim of Robert Alexy’s criticism of legal positivism is that there is a necessary connection between morality and the content of law, and that the separation thesis is thus false. In his earlier writings Alexy adduced three distinct arguments in support of the connection thesis: the argument from injustice, the argument from principles, and the argument from the necessary claim of law to correctness. He later substituted for these a more general argument from the dual nature of law. Alexy situates his critique within the perspective of a participant, as distinguished from the perspective of an observer. Sieckmann maintains that Alexy changed the focus of the debate about legal positivism from an exclusive concern with questions of legal validity to a more general concern with questions of the nature of law by emphasising that in addition to the usual classifying connections between morality, on the one hand, and legal systems, acts and norms, on the other, there are also qualifying connections. Sieckmann concludes that Alexy showed legal positivism to be a not fully satisfactory theory of law for those adopting the participant’s perspective.

Kirste discusses legal scholars who were active in the nineteenth and twentieth centuries, identifying four main types of German legal positivism – jurisprudential, sociological, naturalistic, and statutory positivism – and a fifth type that he calls the general theory of law. His idea is that these theorists were legal positivists because they shared an epistemological aim, namely, establishing legal science as a science in its own right, independent of both the natural and the social sciences, and because they held that the only law is positive law in the sense of enacted norms or customary norms. He considers the theories of Hans Kelsen and Gustav Radbruch as examples of legal positivism. He points out that legal positivism lost its dominance in the wake of the post-World War II revival of natural law theory but soon reasserted its influence through the likes of Ota Weinberger, Niklas Luhmann, and Norbert Hoerster. He also notes that, since the late 1960s, authors such as Peter Koller and Ottfrid Höffe have focused on overcoming the gulf between natural law theory and legal positivism.