Abstract
Any correct assessment of Hans Kelsen's conception of Ought must take into account, first, that Kelsen's theory evolved over some 60 years which saw several major changes of its fundamentals; and second, that the Pure Theory must basically be understood as a meta-theory of institutionalised legal science. With these provisos, Kelsen's explanation of the Ought oscillates between two extremes: at one extreme, the legal Ought is just a formal semantic marker delimiting the realm of the law; at the other, the legal Ought might be conceived of as 'depersonalised will'. Kelsen's most profound and fertile explanation, however, identifies the legal norm with the normative judgment of legal science, while the Ought plays the role of a category (in a Kantian sense) vesting the judgment with normative force