The Ratio Decidendi through Mexican Lens

In March 2021, the Mexican Constitution was amended to transition to a system of precedents. This amendment mandates that the “reasons” of Supreme Court rulings will be binding on the lower courts. However, the reform is rooted in a long-standing practice of ‘Tesis’, i.e., abstract statements that the Court itself identifies when deciding a case. Moreover, there is no consensus as to what these reasons are and why they should be binding. The aim of this article is to identify the possible conceptions of reasons to explore the Court’s different judge-made law roles. Different common law conceptions of the ratio decidendi are used as “mirrors” to identify four models of judicial lawmaking in Mexican practice, namely: judicial legislation, implicit rules, moral-political justifications and social categories. Although the first model seems to prevail, the others provide means for a broader understanding of how the Court creates law depending on the interpretative context in which it operates.