Enneads II.1: Of the Heaven
Aristotle Has to Depend on Quintessence
On the contrary, in the system of Aristotle, the immutability of the stars is easily explained, but only after accepting his theory of a fifth element (the quintessence). If, however, it be rejected, it would be impossible to demonstrate that the heaven, let alone its parts, the sun and the stars, do not perish, while (as Aristotle does) we regard the body of the heaven as being composed of the same elements as terrestrial animals.
PLOTINOS’S VIEWS SUPPORTED BY THE HEAVEN’S POSSESSION OF THE SOUL AND BODY.
As every animal is composed of soul and body, the heaven must owe the permanence of its individuality to the nature either of its soul, or of its body; or again, to that of both. On the hypothesis that its incorruptibility is due to the nature of its body, the Soul’s only function will be to animate it (by uniting with the body of the world). On the contrary hypothesis that the body, by nature corruptible, owes its incorruptibility exclusively to the Soul, there is need of demonstration that the state of the body does not naturally oppose this constitution and permanence (for, naturally constituted objects admit of no disharmony); but that, on the contrary, here matter, by its predisposition, contributes to the accomplishment of the divine volition.