Thomas Aquinas’ Doctrine of Distinctio (Compositio) Realis

The article analyses Thomas Aquinas reflection of the problem of being. An explanation of the structure of an existing thing is raised and crystallized into distinctio (compositio) realis doctrine. The core of this doctrine is the stating of real difference between the essence of being (essentia) and the act of being (esse or actus essendi). Thomas Aquinas refers to Aristotle’s doctrine of substance, takes the concepts of the act and of possibility from it but gives a new meaning to them: every material being is composed by the actualisation of its matter performed by the form, but this process, in turn, is actualised by the act of a different kind, the act of being. The signification of the notion of the difference between the essence and the act of being in every substance is analysed with emphasis on the fact of the misunderstanding of this doctrine of Thomas Aquinas by his own disciples and by the future generations of the Thomistic school. In the second part of article, the arguments of this doctrine are presented focusing on Thomas Aquinas’ conception of the singularity and causality. Finally, in the third part of the article, the question of the method of the cognition of the act of being and the distinction between ratio and intellectus is raised and accentuated. The hypothesis of the confrontation of the philosophies of Thomas Aquinas and Henri Bergson is also suggested