 Indeed, most accounts of knowledge in the dialogues are carried out in the context of such discussions. Even in the Theaetetus, the dialogue most often thought of as dedicated to epistemology, we find the same theme. When he argues against Protagoras’ relativism, Socrates gets the sophist to concede that some people are wiser than others when it comes to what is good for the city (167c–d). Socrates then seizes upon an analogy with medicine. While each person may be the final authority for himself when it comes to what is hot, dry, and sweet for him, in matters of health and disease not everyone knows the healthy for himself nor is he able to cure himself. Just so, while Protagoras may hold that for each city what is fine or base, just or unjust, pious or impious is what the city takes it to be, what is really advantageous for the city is not the same as what it takes to be advantageous (171e – 172b). Although Socrates’ investigation of knowledge becomes more abstract when he introduces being, not-being, likeness and unlikeness, identity and difference, unity and plurality, to this group he adds the fine and the base, the good and the bad (185c–186a). The soul itself investigates these things, trying to determine their being (ousia) and their opposition to one another and the being of that opposition. Finally, the investigation of being, non-being and the other opposites — including the fine and the base, the good and the bad — also reflects both on the being of each and on its usefulness (pros te ousian kai ôpheleian) (186c).While Socrates does not explain what reflecting on their usefulness amounts to, the remark shows a link, however slight, to the original motivation for the investigation of knowledge— i.e., providing what is really advantageous for the city.