This work represents a research on the nature of the causal efficiency of law, i.e. on how the political command is communicated by authority and received by those who must obey it. In the words of political philosophy of aristotelic tradition, it is the classical problem of the “government over free and equal men”, i.e., the problem of compatibility between political government and the freedom of human act and political rights. In the words of kantian practical philosophy, the problem consists (...) in the compatibility between individual’s moral autonomy and juridical system’s heteronomy, i.e. it consists in justifying the dominion of one man over another one, so that the citizen obeys the laws without any kind of submission to a will other than his own. The question requires particular attention to the problem of the nature of political bonds, as communication of political command is necessarily founded on what is common to the members of political society. The work is divided in two parts. The first one proposes a model of practical philosophy whose fundamental structure is common to all major political thinkers of modern times. This model consists in a “moral of obligation” founded on the opposition between law (must) and freedom (will), originated on nominalistic scholastic voluntarism. Within this structure, the problem assumes the form of a dilemma: if law comes from our own will (autonomy), then it becomes necessary to explain how it is possible to command over oneself; if law comes from a will other than our own, then it becomes necessary to explain the difference between law and mere force. In this context, the theories of Hobbes and Rousseau are studied as the theoretical matrix of modern political philosophy and as the two dialectical poles of this opposition. The conclusions derived from the study of these two thinkers are then applied to Kelsen and Kant respectively. The second part proposes a reconstruction of classical philosophy’s position about this problem, meaning by “classical” the tradition that begins with Plato, continues with Aristotle and reaches a new summit with Saint Thomas Aquinas. In this part of the work, a “classical” model of practical philosophy, common to these three authors, is presented. This model consists in an “order of loves”. Two fundamental theses are proposed. The first one is that law is a rational communicable order, whose efficacy is founded on participation of the act of “imperium” of authority in individual’s subjective “imperium” over his own acts. The second one is that the principle of this communication consists in “political concord”, i. e. a “useful friendship” about the ends of society, and that the concrete realization of this order in the citizen’s soul is political virtue, which is analogue to man’s virtue with the same platonic analogy that exists between man’s soul and the city or the State. (shrink)