 Nevertheless, these passages from the Theaetetus draw our attention to a change in the notion of epistêmê. Knowledge of the forms tends to become an end in itself; and in this way the idea of knowledge as pure theory begins to make an appearance in the dialogues. This tension is also prominent in the Republic, of course, where Socrates introduces and develops the notion that rulers should be philosophers, who are defined by their knowledge of forms. At the beginning of the discussion of philosophical rulers in Republic IV, knowledge and craft fall into a familiar pattern of interchangeability. After defining the three classes in the city, Socrates is looking for the knowledge (epistêmê) in virtue of which the city is well-counseled. He dismisses the crafts of carpentry, smithing, and farming — obviously crafts and called epistêmai (428b–c). While these focus on some partial good for the city, the epistêmê of ruling takes counsel for the city as a whole and what is best for it internally and externally (428 b–d). Then, in Republic V, Socrates introduces an altogether different notion of the knowledge that philosophers will have — one whose object is forms. Indeed this passage defines for most readers Plato’s idea of epistêmê.