For a long time, based largely on the Meno, I've been under the impression that Plato interdefines knowledge and teaching. Here is the idea:
- Teaching is the imparting of knowledge.
- Knowledge is what can be taught to every one who is willing and has sufficient learning abilities.
Platonic knowledge thus must be of a non-indexical, atemporal, non-relative reality. And all this follows from Plato's understanding of teaching.
Moreover, teaching is not indoctrination. It is not the mere transmission of opinion or even the turning of knowledge into opinion. It is the imparting of knowledge, so that she who is taught can herself in turn teach. The evidence that the teacher has must itself be evidence that can be imparted to the student. Thus, the evidence, too, must be non-indexical, atemporal and non-relative, accessible to people of all times, cultures and social classes (think of the slave boy) who have sufficient ability. This does not require the theory of recollection--a divinely implanted faculty or knowledge that we receive by illumination at conception will do the trick, too--but does seem to require something special and universal like it.
Furthermore, a part of what it is to teach is to show how the knowledge withstands Socratic questioning--this questioning, thus, is a part of the teaching process, and the knowledge must be something that can survive this.
Or so, on this reading, Plato thinks. Whether it is all true is another question.