Here is the hypothesis: If virtue is some sort of knowledge, it will be teachable. Since virtue is also a good thing (it isn't - it is simply the characteristic of good things, just as bravery is the characteristic of brave things), if we find that all good things involve knowledge, then virtue will also be a knowledge, and then we'll know that it is teachable. Socrates gives Meno many opportunities to object, but Meno does not think critically, unlike Plato's readers.