Summary: This article expounds the thought, on the a priori foundation of law, of Adolf Reinach, a German phenomenological philosopher, disciple of Edmund Husserl and friend and teacher of Edith Stein. It is precisely from within Edith Stein’s thought on th State, that Reinach’s studies are presented here. Neither the empirical law nor the historic State is the object of analysis there, but the “idea” of each. “Idea” here being understood in the phenomenological sense of essence, since as Husserl said, in the first volume of Ideas, phenomenology is a science of essences. Nonetheless, the point of departure will always be an empirical object, since ideation always takes place following that which is given and experience understood as lived experience (Erlebnis). Thus too, the idea of the State, and the historical State itself, will have to be founded on law that is prior to history itself.