Meno

All you need to know about the Meno dialogue is that Plato uses it to argue that all of our knowledge is innate: that, remember, means that we are born with this knowledge. Strictly speaking, we never learn anything, we just remember what we already know.

Plato argues for this by having an uneducated slave boy prove an important truth of geometry just by asking him questions. The boy apparently already knew the truth, and Plato just had to get him to remember by asking the right questions.