For Socrates, the virtues are a kind of knowledge, and the virtues form a unity. Sometimes, Socrates suggests that the virtues are all ‘one and the same’ thing. Other times, he suggests they are ‘parts of a single whole.’ I argue that the ‘what is x?’ question is sophisticated, it gives rise to two distinct kinds of investigations into virtue, a conceptual investigation into the ousia and a psychological investigation into the dunamis, Plato recognized the difference between definitional accounts of (...) the ousia and a psychological accounts of the dunamis, and the distinction between these two investigations can effectively resolve various interpretive puzzles regarding the unity of the virtues. It is argued that the virtues are ‘one and the same’ psychologically, while they are ‘parts of a single whole’ conceptually. (shrink)