I provide a novel interpretation of Aristotle's account of the unity of soul, treating it as resolving the apparent incompatibility of the existence of psychic parts and the soul's status as a unifying form. This incompatibility, I contend, rests on a problematic assumption: mereological actualism, or the claim that parts are actually distinct and prior to the whole. Aristotle successfully undermines actualism and formulates an alternative conception of parthood within De Anima's figure-soul analogy. As triangles are only potentially present within quadrilaterals, so lower psy-chic parts are potential parts of higher souls. This picture treats a soul not as a mere aggregate of capacities, but as essentially unified and prior to its parts. Finally, I argue that this picture can be illuminated and must be read against the background of his hylomorphic account of the unity of form given in Metaphysics H.6.