The main purpose of this paper is to formulate a systemic-legal approach for the analysis of social systems. To this end, three typologies of consensus called limits of the social system are proposed: normal consensus, normative consensus and legitimate consensus. The function of these typologies is, first, to elaborate an explanation about the constitution and democratization of political power, based on the rule of recognition and the basic norm of a State; secondly, to postulate two normative methodologies, a positive registration and a positive demarcation, because of deploy on the structure of the social system a process of emerging legality, whose function is, thirdly, regulate, feedback and optimize the functioning of the political constitution. Finally, the concepts of completeness and legitimacy of the normative system are analyzed, in order to define the institutional scope that a legal system must possess over the cultural subsystems of the social system.