Book I, Chapter 2

In investigating the soul it is necessary, while raising the difficulties about the points on which we must afterwards find our way, to take in as we go along the opinions of our predecessors — all those who declared anything about it — so that we may adopt what has been well said, and, if anything has been said badly, may be on our guard against it. The beginning of the inquiry is to set out what most of all seems to belong to the soul by nature.

Now the ensouled seems to differ from the unensouled chiefly in two respects: in movement and in perceiving. And it is roughly these two that we have received from our predecessors as accounts of the soul. For some say that the soul is above all, and primarily, that which causes movement. But thinking that what is not itself moved cannot move anything else, they supposed the soul to be one of the things that are moved.

Hence Democritus says that it is a kind of fire and hot. For, the shapes and the atoms being infinite in number, he says that the spherical ones are fire and soul — like the so-called motes in the air, which are seen in the beams that come through our windows; and the whole seed-mixture of these he calls the elements of the whole of nature. Leucippus says the same. Of these atoms, the spherical ones are soul, because figures of that sort are best able to slip through everything and, being themselves in movement, to move the rest; and they suppose that the soul is what supplies movement to animals. Hence they hold that respiration is the boundary-mark of living. For when the surrounding air compresses bodies and squeezes out those of the figures that supply movement to animals — since these are themselves never at rest — help comes from outside, other such figures entering in as the animal breathes; for these prevent even the ones already present in animals from being expelled, by joining in holding back what compresses and congeals; and animals live for just so long as they are able to do this.

What is said by the Pythagoreans seems to have the same import; for some of them said that the soul is the motes in the air, and others that it is what moves these motes. They have been mentioned because they are seen to be in continuous movement, even when there is a complete calm.

Those too tend in the same direction who say that the soul is what moves itself. For all these seem to have supposed that movement is what is most proper to the soul, and that all other things are moved by the soul, but the soul by itself, because they see nothing that causes movement without itself also being moved.

Similarly Anaxagoras too says that the soul is that which causes movement, and so does anyone else who has said that intellect set the universe in motion; yet not altogether as Democritus does. For Democritus simply identifies soul and intellect; for the truth, he holds, is what appears, and hence he says that Homer did well when he wrote that Hector lay thinking other thoughts. So he does not employ intellect as a faculty concerned with truth, but says that soul and intellect are the same. Anaxagoras is less clear about them; for in many places he says that intellect is the cause of what is noble and right, but elsewhere that this intellect is the soul, since it belongs, he says, to all animals, both great and small, both honourable and less honourable. But intellect in the sense of practical wisdom does not appear to belong alike to all animals, nor even to all men.

Those, then, who fixed their attention on the fact that what is ensouled is in movement supposed the soul to be that which is most capable of causing movement; whereas those who fixed on its knowing and perceiving the things that are, these say that the soul is the principles, some making these many, others making it this one principle. So Empedocles makes it out of all the elements, and holds that each of these is also soul, speaking thus.

In the same way Plato too, in the Timaeus, makes the soul out of the elements; for like is known by like, and things are made out of the principles. Similarly it was determined in the discourses On Philosophy that the Animal-itself is composed of the Idea itself of the One together with the primary length and breadth and depth, and the rest in like manner. Again, it was put in yet another way: intellect is the One, knowledge the Two — for it proceeds in a single way to a single conclusion — opinion the number of the plane, and perception the number of the solid. For the numbers were said to be the Forms themselves and the principles, and they are made out of the elements. And things are discerned some by intellect, some by knowledge, some by opinion, some by perception; and these numbers are the forms of things.

And since the soul seemed to be both capable of causing movement and capable of knowing, some accordingly wove the two together and declared the soul to be a self-moving number. But they differ about the principles, as to which and how many they are — above all those who make them corporeal differ from those who make them incorporeal, and both from those who mixed the two and declared the principles to be drawn from both. They differ too about their number: some say there is one, others many. And it is in accordance with these views that they render their account of the soul as well; for they supposed, not unreasonably, that what causes movement is by nature among the primary things.

Hence it seemed to some that the soul is fire; for fire is composed of the finest parts and is the most incorporeal of the elements, and moreover it is itself moved and moves the other things primarily. Democritus has stated the matter more elegantly, in declaring why each of these two things holds. For soul, he says, is the same as intellect, and this is one of the primary and indivisible bodies, and is capable of causing movement because of the smallness of its parts and because of its shape; and of the shapes, he says, the spherical is the most easily moved, and intellect and fire are of this shape.

Anaxagoras, as we said before, seems to say that soul and intellect are different, but he treats both as a single nature — except that he sets down intellect above all else as the principle; at any rate he says that it alone of the things that are is simple, unmixed and pure. And he assigns both functions to the same principle, both knowing and causing movement, saying that intellect set the universe in motion.

Thales too, from what is recorded of him, seems to have supposed the soul to be something capable of causing movement, if indeed he said that the stone has a soul because it moves iron. Diogenes, like certain others, held the soul to be air, thinking that air is of the finest parts of all things and is a principle; and that for this reason the soul both knows and causes movement — in so far as air is primary and the rest come from it, it knows, and in so far as it is finest, it is capable of causing movement. Heraclitus too says that the principle is soul, since it is the exhalation out of which he composes everything else; and it is the least corporeal of things and ever-flowing; and what is in movement is known by what is in movement. He, like most people, thought that the things that are, are in movement.

Alcmaeon too seems to have supposed much the same about the soul; for he says that it is immortal because it resembles the immortals, and that this belongs to it in that it is always in movement; for all the divine things also move continuously and for ever — moon, sun, the stars, and the whole heaven.

Among the cruder thinkers, some declared the soul to be water, as Hippo did. They seem to have been persuaded by the seed, because the seed of all animals is moist; for Hippo refutes those who say that the soul is blood, on the ground that the seed is not blood, and that the seed is the primary soul. Others say it is blood, as Critias did, supposing that perceiving is what is most proper to the soul, and that this belongs to it because of the nature of blood. For all the elements have found a supporter except earth; earth no one has declared for, unless someone has said that the soul is composed of all the elements, or is all of them.

They all, one may say, define the soul by three things: movement, perception, and incorporeality; and each of these is traced back to the principles. Hence even those who define it by knowing make it either an element or composed of the elements, all of them speaking alike, with one exception; for they say that like is known by like, and since the soul knows all things, they compose it out of all the principles. Those, then, who say that there is some one cause and a single element also set down the soul as one thing, such as fire or air; while those who say that the principles are many make the soul many as well.

But Anaxagoras alone says that intellect is unaffected and has nothing in common with anything else. Yet how, being of this kind, it will know, and through what cause, he has neither said nor is it evident from what he has said. And those who posit contrarieties among the principles compose the soul too out of the contraries; while those who take one of the pair of contraries — the hot, say, or the cold, or something else of that sort — likewise set down the soul as one of these. Hence they also follow the names: those who say it is the hot, because living (zēn) has been named from this; and those who say it is the cold, because the soul (psuchē) is named from respiration and cooling.

These, then, are the views about the soul that have been handed down, and the reasons for which they are stated as they are.