Constitutional democracy is a complex political system, based on legal limits and links imposed on all powers, public and private, state and supra-state, for the protection of peace and the fundamental rights of all. The formal theory of law elaborated in this first volume of Principia iuris defines the normative paradigm of constitutional democracy, analyzes the growing divergence between its principles and its practices and illustrates the techniques and guarantee institutions capable of overcoming, or at least reducing , the inefficiency of the former and the illegitimacy of the latter. In opposition to the current crisis of legal and political reason, a rigorous reconstruction of the totality of theoretical legal language is proposed here thanks to the unprecedented use of the axiomatic method, which shows to be a powerful instrument of clarification and conceptual simplification, logical control, critical analysis, theoretical invention and political and institutional planning.