On the Nature of Man

1.1Whatever comes to be comes from the soul. A body that exists only in potency cannot house life by itself. Elsewhere one may possess a power and leave it idle — sight unused — yet the soul admits no such idle possession. Even in sleep psychic work continues: nourishment, growth, imagination, breath, the marks of life. So life is never a mere potency waiting to be switched on; it is always already in act. The soul's form-giving is the soul itself. Life is native to the soul and reaches the body only by share. To treat bodily health as if it were the soul's life is a sophistic slide from body to soul.

1.2A body can take on opposed qualities in its matter, but not in its form: change the form and you change the thing. Contraries therefore sit in the underlying body, not in the form as such. That is why the soul cannot be the body's entelechy. It stands as its own complete, bodiless substance, able to receive virtue and vice — opposed states no mere form could host. Call the soul an entelechy and you make it motionless in itself, moved only by accident; yet the body does not move itself. Whatever first moves it must come from the soul.

1.3Where does the body's motion come from, if not the soul? The body is not a self-mover. Appeals to elemental lightness and heaviness do not give a first beginning of motion; they give a later account. Light and heavy things do come to rest in their places — so those qualities are not perpetual motion itself. Still less can thinking, judging, and forming opinions be the work of weight. The world, the sun, and the moon move by nature and cannot naturally stand still. So too the soul: by nature it is always in motion, and natural rest would be its undoing.

2.1Some make the soul a body, and some of them name it blood (or breath). If soul were simply blood, quantity of blood would be quantity of soul. Yet blood is made from food and passes into flesh and the body's other parts; it is poured and divided. The soul is not emptied out that way. Even living things that seem without blood show that life is not the same as blood. Blood may serve life; it is not what the soul is.

2.2Others call the soul breath or air. Air is a body — spread out and shoved about. If soul were only that rush of air, life would last only while breathing lasts. The soul is not the air that enters and leaves. So the soul is not pneuma.

2.3Some say the soul is only a tuning — a harmony of the body. But if learning is recollection, the soul must already be something before this body's tuning. The soul can resist the body and govern it; a harmony does not command the lyre. Harmony grows tighter or looser; soul does not become more or less soul. Break the instrument and the tuning is gone; the soul is not dismissed with a broken frame. So the soul is not harmony. The lyre image meets the answers already given in Plato's Phaedo.

2.4Pythagoras loved to speak of God and the world in numbers, and he pictured the soul as a self-moving number; Xenocrates followed. The point is not that soul equals a numeral, but that soul works among countable, many things, sorting them by form. Quantity is what number is; substance is what soul is — so soul is not number. Number breaks into discrete units; soul holds together. Number is even or odd; soul is neither. Add units and number grows; soul does not grow by addition. Soul moves itself; a fixed number does not. A number keeps one nature and cannot trade qualities; the soul stays one substance while passing from ignorance to knowledge and from vice to virtue. Therefore the soul is not number.

3.1Are souls still being made? If they arise now only by providence, not by creation, the account falters. Moses says God rested from all his works which he had begun to make (Genesis 2:2). Keep creating souls today and that rest is emptied. Make them by bodily succession instead and you drag them into the mortality of generated things. Both roads are absurd; so souls are not now coming to be. When it is said 'My Father is working still' (John 5:17), the sense is providence, not minting new soul-essences.