Starting from recent systemological research and the debate on the comparative method, the paper first proposes a reflection on the heuristic validity of the typological categories of private and public comparative law and their use to study the trans-nationalization and glob-alization phenomena. In the same perspective, the analysis focuses on the "deformalization" attempts of classical legal science (especially constitutional), in the view of a realist approach more attentive to the issues of living law and concrete subjects of the legal system. The analysis, therefore, addresses the issues that have characterized the formation of the primary law of the Union. In addition, the paper examines the case-law of the Court of Justice that contributed to the jurisprudential recognition of fundamental rights at the European level, making use for this purpose of the "constitutional traditions common to the member states of the Union". Finally, the conclusions propose a question relating to the right to form jurisprudence of the Union in the field of protection of fundamental rights. From a systemological point of view, this leads to the question of whether it is a peculiarity of the European legal system, or a case study intended to influence, if not also the origin, the developments of the legal systems at the global level in this matter.