In the dialog The Meno by Plato, the question is asked Can virtue be taught? Socrates asks What is virtue? Plato was the mouthpiece for Socrates who never wrote anything down. He wrote 35 dialogues in which Socrates appears as the main character most of the time. By asking a question you implicitly assume certain things. By asking the question what is justice? you assume justice is something that can be defined. This is the means Socrates baits his listeners.
Meno attempts to give examples of what virtue is. But Socrates insists that Meno give an every and only definition of what virtue is. If Socrates asked what even numbers are, it would take forever to list the even numbers/provide an answer to what even numbers are. Even numbers are numbers divisible by 2. That is something every even number has in common and is only attributable to even numbers. Well of course Meno cant do it.
He cant give an every and only definition for what virtue is. He cannot generalize what virtue is. He cannot extrapolate/extract the quality of what his examples of virtue have in common and put it into a single definition that applies to all those examples. For completeness of the dialogue Meno, Meno then attempts to say If you dont know what it is you are looking for, then you have no basis upon which to search for it. And if you do know what you are looking for, then indeed you have no need to go about searching for it. (Sophism word games inc.)
Then Socrates goes demonstrates this is false by having Menos slave boy be led to understand what the Pythagorean theorem is by drawing lines in the sand. Socrates does not tell him what it is. He only leads him to the answer and the slave boy tells him. How can this be possible? Socrates then goes on to (un-Greek-like) say how all knowledge is recollection. That he knows it from the Forms (roughly heaven where we all come from) and previous lives. He knows it from transmigration of the soul/reincarnation. The slave boy re-collects the knowledge he already had is the idea. So that is how we learn by recalling what we already knew. We know it when we see it. (Virtue/by example) even though we cannot provide an exact definition of it.
Then it goes into the idea of whether virtue is teachable or not. Socrates leads Meno to believe that for something to be teachable, it must be knowledge. It has an every and only definition. But then he points out that it must NOT be knowledge because if it were, it would be taught. Since virtue is not taught, it must not be knowledge. Virtue then being something that we intuit when we say I know it when I see it we recollect it from the soul. That is the idea Plato presents in the dialogue The Meno through Socrates and the character Meno.
I do not disagree with Plato on this at all. Some things we do know by intuition. In fact I take this further than he does. It should be noted that reincarnation is very un-Greek-like. The Homeric heros like Achilles and Agamemnon were not reincarnated in the Iliad Trojan War. These ideas Plato got from the Pythagoreans who in turn got it from the River Valley Civilizations like the Tigris and Euphrates rivers (Iran) and Indus Valley (India).
In any case, can virtue be defined? I will make such an attempt in the next post and we will see what sort of problems surface.
With a rather firm hand if necessary! 
