Meno is a Socratic dialogue written by Plato. Written in the Socratic dialectic style, it attempts to determine the definition of virtue, meaning in this case virtue in general, rather than particular virtues (e.g., justice, temperance, etc.). The goal is a common definition that applies equally to all particular virtues.
The dialogue starts with Meno asking Socrates to tell him what virtue is. Socrates, in his usual style, professes ignorance. Meno suggests that there are many different types of virtues, for example, some are appropriate for men, some for women, some for slaves, others for children. Socrates does not accept this explanation, but instead wants to know what is the common quality that makes all these different things virtues.
The conversation continues, with Socrates and Meno able to list many particular virtues, but unable to find the thing which they all have in common and which makes them all virtues — until Meno proposes desire for good (in the moral sense) things as the definition.
Socrates questions this definition, suggesting that no one knowingly desires evil, and thus the desire for good is common in all men. Meno adds that the good things must be obtained in the right way, so being wealthy would be a virtue if the wealth were obtained in a just way. Socrates spots a circular argument at this point, with virtue being defined as that which is obtained in a virtuous way. Meno gives up at this point, saying:
"For my soul and my tongue are really torpid, and I do not know how to answer you; and though I have been delivered of an infinite variety of speeches about virtue before now, and to many persons – and very good ones they were, as I thought – at this moment I cannot even say what virtue is." (80b)
At this point, Meno introduces an epistemological problem: "And how will you enquire, Socrates, into that which you do not know? What will you put forth as the subject of enquiry? And if you find what you want, how will you ever know that this is the thing which you did not know?" In other words, how is one to know when one has arrived at the truth when one does not know what the truth is?
Socrates suggests that all acquisition of knowledge is in fact a matter of anamnesis (sometimes translated as recollection, reminiscence, or recall). We never really learn anything; we already know it and only need a reminder. A famous demonstration of this theory ensues: Socrates, through gentle prodding of one of Meno's slaves, elicits a simple geometrical theorem from the boy, though the boy had not before even considered the matter.
Since no one really learns anything, there are no teachers or students, so virtue cannot be taught. This means Meno must redefine virtue.
Without defining virtue, the Meno concludes with Socrates saying:
"Then, Meno, the conclusion is that virtue comes to the virtuous by the gift of god. But we shall never know the certain truth until, before asking how virtue is given, we enquire into the actual nature of virtue [something that Plato doesn't discuss in detail until The Republic]. I fear that I must go away, but do you, now that you are persuaded yourself, persuade our friend Anytus. And do not let him be so exasperated; if you can conciliate him, you will have done good service to the Athenian people." (100b)