Plato conceived all the material things 'down here' to be deficient in some way. Their perfect counterparts, constituting the essence of those material things, reside outside the latter.
Aristotle, however, conceived the material things 'down here' to be totally self-sufficient. Their essence resides within them. He nonetheless was looking for "Separate Entities" to exist somewhere, as beings of another nature all together (See OWENS, J., 1978, The Doctrine of Being in the Aristotelian "Metaphysics").