While the body is young and fine, the soul blunders, but as the body grows old it attains its highest power. Again, every good soul uses mind; but no body can produce mind: for how should that which is without mind produce mind? Again, while the soul uses the body as an instrument, it is not in it; just as the engineer is not in his engines (although many engines move without being touched by any one).

VIII. On Mind and Soul, and that the latter is immortal. - On the Gods and the Cosmos