The relevance of Hans Kelsen for contemporary legal science is unquestionable: founder of the general theory of law, theoretical maxim of representative democracy and father of rigid and concentrated constitutionalism. Abounding in this importance, and in the light of the new paradigm of constitutional democracy, Luigi Ferrajoli proceeds in this book to a systematic reconstruction of the theses of the pure Kelsenian theory, showing its merits but also its contradictions. In particular, it points out and treats in all its depth ten aporías present in the work of Kelsen. An analysis that goes far beyond mere historiographic interest, but which can not be reduced to a simple academic question of legal epistemology. In turning the kelsenian thesis of the non-applicability of the logic to the right, the relation between law and logic is identified for Ferrajoli with the question of the normativity of the constitutions and of the construction of the constitutional democracy through the imposition Of the guarantees logically implied by constitutionally established rights, to politics and law, to legislation and to jurisdiction. The logic of law thus forms part of a work of constant reform and integration of the law in force and, thus, the difficult and always incomplete construction of democracy.