not know what to look for.
He does not himself believe this though, as the dilemma can be resolved by what Socrates claims he has learned from the "priests and priestesses whose care it is to be able to give an account of their practices" and also by Pindar. What he has learned is that the soul is immortal and that our present life is only one chapter in history. Socrates explains that at some point our souls have learned everything there is to know, at that certain things have been temporarily forgotten, and need to be reminded, by asking the right questions and through study and diligence. Socrates explains how learning is not then as it seems, but is rather a process of "re-call".
To attempt to prove this to Meno, Socrates uses a slave boy to answer a series of geometric problems. The slave boy has had no prior mathematical instruction to date, and yet was able to come to the right solutions, with the help of Socrates asking him certain questions, and it was shown that he must be recollecting prior knowledge. This is Socrates' way of proving that the soul is immortal, as the boy must have been taught geometry "before he was a man". As far as the argument goes it is quite effective, but it is not proof in itself of the soul's immortality. It demonstrates that the soul may have existed once before and learned everything there is to learn, but this does mean that the soul necessarily lives on after the body's death.
Immortality receives another argument in the Republic. The ancient subtitle for this work was "On Justice", but in fact the work goes much deeper than this and many different subjects were discussed. Justice though is what leads Plato on to the topic of immortality as Socrates is explaining to Glaucon the "rewards and prizes that have been proposed for virtue". Socrates remarks how short human life is in comparison to the world and the universe, and that the soul must be immortal because it cares about what happens...