Proceedings of the American Catholic Philosophical Association

Volume 81, 2007

Freedom, Will, and Nature

Thomas Aquinas on the Ontology of Amicitia
Unio and Communicatio

The purpose of this paper is to highlight the ontological character of amicitia in Aquinas. The originality of Aquinas’s theory is found in the ontological foundation expressed by Neoplatonic concepts (unio, unitas, communicatio). By integrating such Neoplatonic concepts with his analysis on the transcendentals (aliquid, unum), I made a new ontological foundation to the theory of amicitia. In order that a man is a one (unum), he must establish himself as something different (aliud quid) in the midst of the relationship with others and then has to return to himself. So long as he stays self-contained without moving outward, he cannot constitute himself as an independent being which is different from other beings (aliquid). The ontological oneness (unitas) as an independent rational substance makes it possible for a man to form the mutual relationship of unity (unio) without losing himself in the midst of the deep relationship with someone else.