This ancient paradox is named for a character in Plato’s eponymous dialogue. Socrates and Meno are engaged in a conversation about the nature of virtue. Meno offers a series of suggestions, each of which Socrates shows to be inadequate. Socrates himself professes not to know what virtue is. How then, asks Meno, would you recognize it, if you ever encounter it? How would you see that a certain answer to the question “What is virtue?” is correct, unless you already knew the correct answer? It seems to follow that no one ever learns anything by asking questions, which is implausible, if not absurd.
Socrates’ solution is to suggest that basic elements of knowledge, enough to recognize a correct answer, can be “recollected” from a previous life, given the right kind of encouragement. As proof he shows how a slave boy can be prompted to solve geometrical problems, though he has never had instruction in geometry.
Although the recollection theory is no longer a live option (almost no philosophers believe in reincarnation), Socrates’ assertion that knowledge is latent in each individual is now widely (though not universally) accepted, at least for some kinds of knowledge. It constitutes an answer to the modern form of Meno’s problem, which is: how do people successfully acquire certain rich systems of knowledge on the basis of little or no evidence or instruction? The paradigm case of such “learning” (there is debate about whether “learning” is the correct term) is first-language acquisition, in which very young (normal) children manage to acquire complex grammatical systems effortlessly, despite evidence that is completely inadequate and often downright misleading (the ungrammatical speech and erroneous instruction of adults).