Communication can be monologic or dialogical. Only the latter forms are an essential characteristic of legal reality. At the same time, dialogue is conceived as an immanent feature of sociality as such. In the process of identity formation and personality socialization, dialogue is necessary and inevitable. The process of dialogic socialization ensures the reproduction of any society. Society exists only in case if there is recognition of mutual legal claims, i.e., legitimacy of law. The principle of universal trust as a constitutive foundation of sociality is at the same time the fundamental principle of a legal system. These initial philosophical and legal provisions require explication in the actual legal refraction. Designation of social situations as legal, attributing legal features to them, involves correlation of personal intention with the legal status of the Self and the counterparty in a legal relationship or in a simple form of realization of law. Thus, the relation I-You is mediated by the legal instance of It. However, it is quite difficult to measure the reciprocity of recognition of the Other as a bearer of legal status in empirical reality, especially in the field of public law. The criteria of “extreme injustice” (G. Radbruch’s formula) and “aggressive violence” (in the terminology of V.A. Chetvernin) can be used to explicate the legitimacy of law and can be specified in sociological and legal studies. This paper states the paradox of measuring of the legitimacy of law, which consists in the difference between trust in an empirically given countersubject in a legal relationship, and impersonal status of a legal institution. Trust in the institution, according to the authors, extends, among other things, to a critical attitude towards it, however, with the condition if there is a recognition of the need for its existence. Another paradox of the legitimacy of law, considered in the article, is associated with the antinomy “the ideal — the real.” Violations (non-observance) of legal norms, if they are not widespread, do not put into question the legitimacy of the legal system as a whole. In general, the recognition of law is determined not by the average result of a sociological survey, but by the understanding of the necessity and the inevitability of the Other as a carrier of a typified legal status (for example, in criminal proceedings: in recognizing the interdependence of the Self from Others as carriers of the status of subjects of law).