Still, a fear is expressed that the soul upon leaving the body may vanish away like smoke or air. Socrates in answer appeals first of all to the old Orphic tradition that the souls of the dead are in the world below, and that the living come from them. This he attempts to found on a philosophical assumption that all opposites--e.g. less, greater; weaker, stronger; sleeping, waking; life, death--are generated out of each other. Nor can the process of generation be only a passage from living to dying, for then all would end in death. The perpetual sleeper (Endymion) would be no longer distinguished from the rest of mankind. The circle of nature is not complete unless the living come from the dead as well as pass to them. The Platonic doctrine of reminiscence is then adduced as a confirmation of the pre-existence of the soul. Some proofs of this doctrine are demanded. One proof given is the same as that of the Meno, and is derived from the latent knowledge of mathematics, which may be elicited from an unlearned person when a diagram is presented to him. Again, there is a power of association, which from seeing Simmias may remember Cebes, or from seeing a picture of Simmias may remember Simmias. The lyre may recall the player of the lyre, and equal pieces of wood or stone may be associated with the higher notion of absolute equality. But here observe that material equalities fall short of the conception of absolute equality with which they are compared, and which is the measure of them. And the measure or standard must be prior to that which is measured, the idea of equality prior to the visible equals. And if prior to them, then prior also to the perceptions of the senses which recall them, and therefore either given before birth or at birth. But all men have not this knowledge, nor have any without a process of reminiscence; which is a proof that it is not innate or given at birth, unless indeed it was given and taken away at the same instant. But if not given to men in birth, it must have been given before birth--this is the only alternative which remains. And if we had ideas in a former state, then our souls must have existed and must have had intelligence in a former state. The pre-existence of the soul stands or falls with the doctrine of ideas.