In the Phaedrus Socrates compares the soul to a chariot with a charioteer and a pair of winged horses. Whereas the chariot of a god has two good horses, that of a human being has one good horse and one bad, unruly horse that is the cause of much hardship for the charioteer. The soul, he says,
…has the care of inanimate being everywhere, and traverses the whole heaven in divers forms appearing – when perfect and fully winged she soars upward, and orders the whole world; whereas the imperfect soul, losing her wings and drooping in her flight at last settles on the solid ground – there, finding a home, she receives an earthly frame which appears to be self-moved, but is really moved by her power; and this composition of soul and body is called a living and mortal creature.
The chariot of a god is able to soar to the top of the vault of heaven, such that the god is able to step outside the rim of heaven and contemplate the colourless, formless, intangible essence of reality. The revolution of the spheres carries the god round and back again to the same place, and in the space of this circle he feasts his mind upon justice, temperance, and knowledge, not in the form of generation or relation, which men call existence, but in their absolute, universal form.
Despite their bad, unruly horse, the chariots of the imperfect souls that are most alike to the gods are able to ascend high enough for their charioteers to lift their heads above the rim of heaven and catch a fleeting glimpse of the universals. However, the rest are not strong enough to ascend so high, and are left to feed their mind on nothing more than opinion.
In time, all imperfect souls fall back to earth, but only those that have seen something of the universals can take on a human form; human beings are by their nature able to recollect universals, and so must once have seen them. The imperfect souls that have gazed longest upon the universals are incarnated as philosophers, artists, and true lovers. As they are still able to remember the universals, they are completely absorbed in ideas about them and forget all about earthly interests. Common people think that they are mad, but the truth is that they are divinely inspired and in love with goodness and beauty.