Recent debate in moral and political philosophy has been concerned with constructivism. Constructivism is the thesis that objective values are constructions of reason and that their validity is determined by rational criteria. Constructivism poses a challenge to Kelsen's position that justice is a subjective value. Kelsen's critique of practical reason and deontic logic in General Theory of Norms is best understood as a response to constructivism. Kelsen's arguments can be a contribution to contemporary debates about constructivism, particularly the constructivism of Rawls.