Plato’s theory of the tripartite soul is coherent only if he conceives of appetite as non-rational.
Lorenz argues that Platonic tripartition is internally coherent only on the condition that the appetitive part is denied rational capacity, making the non-rationality of appetite a structural requirement of the three-part theory.
, The Brute Within: Appetitive Desire in Plato and Aristotle, 2006thesis