In Republic V, Plato distinguishes two different cognitive powers, knowledge and belief, which operate differently on different types of object. I argue that in Republic VI Plato modifies this account, and claims that there is a single cognitive power, which under different circumstances behaves either as knowledge or as belief. I show that the circumstances which turn true belief into knowledge are the provision of an individuation account of the object of belief, which reveals the ontological status and the nature of the object. Plato explores many alternative candidates of individuation accounts of objects of true belief, which he discards. I conclude with a Platonic sketch of a teleological account of individuation which would satisfy his requirements of turning true belief into knowledge.