The thesis I should like to advance in this essay is that Plato cannot and, in fact, does not adhere consistently to the doctrine that to know the good is to do the good. First, in order to display the paradoxes in the Platonic ethical system, I shall discuss the concept of the homogeneity of the good which Plato explicitly endorses. Second, by referring to Plato's practice, I shall endeavor to demonstrate that he treats the good as heterogeneous although this treatment is inconsistent with his equation of knowledge with virtue. I shall use the descriptive phrase 'homogeneity of the good' to stand for that conception of the good which identifies the good exclusively with the moral good. I shall use the descriptive phrase 'heterogeneity of the good' to stand for that conception of the good which includes in the definition of good mixed pleasures or the natural good. Our understanding of the good as heterogeneous allows us to clarify many of the paradoxes present in Platonic ethics and affords us a deeper understanding of Plato.