How will you look for it, Socrates, when you do not know at all what it is? How will you aim to search for something you do not know at all? If you should meet with it, how will you know that this is the thing that you did not know?
One source of the ambiguity which leads to this paradox is the definition of 'know' as a verb. If there is more than one definition, i.e., if 'know' refers to more than one epistemological action, then one could be said to 'know virtue' and to 'not know virtue' simultaneously. Such homonymic cases are often the foundations for jokes and riddles, such as "what do you call a winter athlete from Warsaw? a ski Pole."
If Socrates claims that he does not understand what constitutes virtue, he says that he does not know virtue. But if he simultaneously can identify an instance of virtue, he can claim to know virtue. Perhaps I do not know what constitutes my favorite soup at a restaurant - I do not know its ingredients - but I certainly know this soup when I taste it - I can identify it: a possible solution to Meno's paradox.
In a reverse situation, I might not be able to identify a thing, but I might understand its constituents. Imagine that I've never tasted borscht, but I've learned that it's a soup made with beets and sour cream and often served at room temperature. If I were blindfolded and offered a spoonful of it, I would not be able to identify it - I would not "know" it - although I understand its composition - I "know" it.
To place the paradox in a different context, imagine that you are looking for something which does not exist. Serious scientists spent years looking for a sample of Phlogiston. They "knew" what they were looking for, and yet how can one "know" what does not exist? Likewise, I can "know" what a four-headed swan is, inasmuch as I can conceptualize and make to myself a representation of such a creature; but I cannot "know" a four-headed swan in the sense of being able to recognize or identify it, because it doesn't exist.
The same would be true of aether, more properly called 'Luminiferous aether', which occupied earnest physicists as late as the early 1900's, when Einstein wrestled with the concept; he eventually rejected it, along with almost all other physicists, although he sometimes confusingly used the word 'aether' to speak of a space-time matrix.
Additionally, we can note a connection to Ockham: if I can't "know" something, being able to neither identify it or understand its composition, then I cannot fit it into a chain of causes and effects. Being unable to locate it in a causal sequence, I cannot call it necessary, and therefore am not justified in positing its existence.
Although philosophy is not philology, we nonetheless should take care to recall that Plato's Meno has been translated for those of us who cannot read Greek. To that end, to be thorough, we include an alternate rendering of the passage:
But how will you look for something when you don't in the least know what it is? How on earth are you going to set up something you don't know as the object of your search? To put it another way, even if you come right up against it, how will you know that what you have found is the thing you didn't know?
Meno's paradox presents us with richer food for thought than the perhaps more popular but silly aphorisms about "knowing nothing" which Plato sometimes places into the mouth of Socrates.
