Starting from the explication of the term “Eidos” or “pure essence” and its correlate in the sphere of meanings, the term “pure concept”, I determine the ontological places of concepts and of essences: propositions and states of affairs. The Husserlian concept of state of affairs, which is the central concept of his ontological conception of the A Priori, is introduced together with the correlative concept of proposition. Universal states of affairs which are built-up by pure essences alone are universal eidetic states of affairs, as such they are a priori states of affairs. These “eidetic laws” are correlates of universal propositions built-up by pure concepts alone and become evident in virtue of their pure concepts. Groups of eidetic laws constitute an Eidos (in the strong sense), an “A priori”: it is an ensemble of eidetic laws which is constitutive for a whole sphere of entities or phenomena falling under a general pure concept.
