It is often held by scholars that Plato's notion of the tripartite soul makes him unable to give an account of the unified soul or personality. The aim of this paper is to tackle this problem by proposing the following three views: first, Plato's account of the soul would not commit him to the view that within the each part of the soul there are sub-divisions; second, the unity and harmony of the soul could not be achieved by violence and conversation, but by education. Finally, by exploring Plato's education programme in The Republic we can see that it is the only efficient means for bringing the three parts into harmony, and makes them one instead of many.