The Six Books of Proclus on the Theology of Plato, Volume 2

For if it is partible, being self-subsistent, it will constitute itself partible,[232] and the whole will be converted to itself, and all will be in all itself. This however is impossible. Hence that which is self-subsistent is impartible. But it is also simple. For if a composite, one thing in it will be less, but another more excellent, and the more will be derived from the less excellent, and the less from the more excellent, if the whole proceeds from itself. Farther still, it would not be sufficient to itself, being indigent of the elements of itself of which it consists. Every thing therefore, which is self-subsistent, is simple.