Ennead IV.7 is a very early treatise, where Plotinus presents the teachings of the main schools current in his day: the Stoics, Epicureans, Pythagoreans, and Peripatetics, all of whom presented soul as something material and neither truly immortal nor imperishable. It includes observations on many mainly Stoic doctrines on perception, memory, sensation, thought, virtue, powers of material bodies, mixture and reproduction; on Pythagorean attunement; and on Peripatetic entelechy. In Chapters 9–10 Plotinus presents Plato's doctrines on soul's immortality—mainly that of the individual soul, but a fortiori that of the soul of the cosmos. These offer some of his most powerful prose. Plotinus is not concerned to prove the soul's immortality—an uncontroversial tenet of Platonism—but rather with laying down the indisputable foundations for his later writings.