Reality

All soul is immortal. For that which is always in movement is immortal; that which moves something else, in ceasing from movement ceases from living. So only that which moves itself, because it does not abandon itself, never stops moving. But is is also source and first principle of movement for the other things which move. Now a first principle is something which does not come into being. For all that comes into being from a first principle, but first principle itself cannot come into being from anything at all; for if a first principle came into being from anything, it would not do so from a first principle. Since it is something that does not come into being, it must also be something which does not perish. For if a first principle is destroyed, neither will it ever come into being from anything itself nor will anything else come into being from it, given that all things must come into being from a first principle. It is in this way, them, that that which moves itself is a first principle or movement. It is not possible for this either for this to be destroyed or to come into being, or else the whole universe and the whole of that which comes to be might collapse together and come to a halt, and never again have a source from which all things will be moved and come to be. And since that which is moved by itself has been shown to be immortal, it will incur no shame to say that this is the essence and the definition of soul. For all body which has its source of motion outside itself is soulless, whereas that which has it within itself, from itself, is ensouled, this, this being the nature of soul; and if this is the way it is - that that which moves itself is nothing other than soul - then soul will necessarily be something that neither comes into being nor dies.

- Socrates in PhAEdrus

And by reason all these affections, the soul when enclosed in a mortal body is at first without sense; but when the stream of growth and nutriment flows in with diminished speed, and the course of the soul attaining a calm go their own way and become steadier as time advances, then the revolutions of the several circles return to their natural figure, and call the same the other by their right names, and make the possessor of them a rational being. And if these combine in him with any true nurture or education, he attains the fullness and health of the perfect man, and escapes the worst disease of all; but if he neglects education he walks lame throughout existence in this life, and returns imperfect and good for nothing to the world below.

-Timaeus