The limitation of act by potency, central in the metaphysics of Thom as Aquinas, has its origins in Plotinus. He transforms Aristotle ’s horizontal causality of change into a vertical causality of participation. Potency and infinity are not just un intelligible lack of limit, but productive power. Form determines matter but is limited by recepti on into matter. The experience of unity begins with sensible things, which always have parts, so what is really one is incorporeal, without division and separation. (...) Unity is like the esse of Thomas, since it is the act that makes a thing what it is and has its fullness in God. (shrink)