This paper aims to demonstrate the strength and sedimentation that have the rule of constitutional principles; i.e., the ability, capacity, and above all the need they have for the final concentration of law embodied in judicial decisions. Initially, we intend to support the philosophy of the existence of this species rules, and its indispensability in enriching the interpretation, settlement and justice of cases entrusted to the judiciary. Not only that, we believe it necessary to demonstrate a modern interpretive activity, in order to bring greater rationality and effectiveness for this task. Finally, the inclusion to the study of a case (hard case) for you to view, in practice, the realization of this whole idea.