Hans Kelsen’s fundamental contributions to legal philosophy are accompanied by seminal work in political theory and on problems of constitutional law and public international law. There are also forays into anthropological speculation, important studies of classical philosophers, most notably Plato, and much more of interest along the way. It is in legal philosophy, however, that Kelsen made his mark. As early as 1934, the erudite Roscoe Pound wrote that Kelsen was ‘unquestionably the leading jurist of the time’ (Pound 1933–4: 532), and to this day many in jurisprudential circles endorse Pound’s assessment.

Three phases of development in Kelsen’s theory can be distinguished: an early phase, ‘critical constructivism’ (1911–21); then the long, ‘classical’ or ‘Neo-Kantian’ phase (1921–60), including in the 1920s the formation, around Kelsen, of the Vienna School of Legal Theory; and, finally, the late, ‘sceptical’ phase (1960–73). The early phase is seen most clearly in Kelsen’s first major treatise, Hauptprobleme der Staatsrechtslehre (Kelsen 1911). One of Kelsen’s central aims in the early phase – but not just there – is to establish legal science as a ‘normative’ discipline, by which he understands a discipline that is addressed to normative material and whose statements are formulated in normative language. Toward this end, he attempts to ‘construct’ the fundamental concepts of the law, for, as he argues, to understand these concepts correctly is to understand them as peculiarly normative – and not, then, as amenable to expression in factual terms.