Full Idea
The rational and irrational parts of the soul are either separate like parts of the body, or are distinguishable only in definition and thought, like the convex and concave aspects of the circumference of a circle.
Gist of Idea
The rational and irrational parts of the soul are either truly separate, or merely described that way
Source
Aristotle (Nicomachean Ethics [c.334 BCE], 1102a27)
Book Reference
Aristotle: 'Ethics (Nicomachean)', ed/tr. ThomsonJ A K/TredennickH [Penguin 1976], p.88
A Reaction
Whether or not the soul is unified was a clear issue for Aristotle, explored further in De Anima (408a15 and 411b10). He appears to say the soul is not a unity, thus disagreeing with Descartes (Med. 6).