Abstract

This paper investigates how unity and distinction coexist within a single being by examining Aristotelian metaphysics of act and potency and their development in Thomistic theology. It argues that identity is the persistence of a substance through change, grounded in the actualization of potency by form. In human beings, this unity-in-difference is achieved through the rational soul, which unifies bodily, intellectual, and affective capacities within a composite being. Drawing on Aquinas, the paper contrasts this created, composite unity with divine unity, where God exists as Pure Act without potency or composition. The study further explains how human identity participates analogically in divine unity, while remaining ontologically dependent and metaphysically distinct from God. Finally, the paper clarifies the contrast between human unity and the Trinitarian unity of God, where real distinctions of persons exist without division of essence, thereby highlighting the metaphysical difference between created participation and uncreated simplicity.