Rhetoric is supposed to make men able to speak, and thus according to Socrates able also to understand what they are speaking about. If this were true, then rhetoric would be a kind of education or a mode of acquiring knowledge.
Gorgias asks a question of Socrates’s question: how could rhetoric not make man able also to understand what they are speaking about? But does it really follow that when one speaks about something one necessarily understands what it is that one is speaking about? No. Is that not why we have the phrase, “you don’t know what you’re speaking about”?