The question of how the legal power of a constitutional court to overturn acts of parliament can be justified is the central theoretical issue in the field of constitutional review. The  thesis of this paper is that constitutional review is justified on the basis of principles theory on the one hand and on the basis of the theory of “argumentative representation” on the other. The norm-theoretic basis of principles theory is the distinction between rules and principles. If the form of application of the rules is subsumption, by contrast, the form of application of principles is balancing. Constitutional rights have essentially the character of principles, and Balancing presupposes scales, which in constitutional law are possible only as crude discrete scales. The legal reasoning implies a new concept of democracy. An adequate concept of democracy must comprise not only decision but also argument.