The Philebus is an important commentary upon the Republic, not simply because it features the question of the Good but more precisely because it answers questions that must have been asked by Plato’s readers. I see it therefore as a companion piece to the Republic. The Philebus is to be dated after the Parmenides, and it has thus often been read after the critique of Forms in the first part of the Parmenides as reflecting Plato’s rejection of a theory of Forms or at least as holding a different view of Forms from that expressed in earlier dialogues such as the Phaedo, Republic, Symposium, and Phaedrus. Since I do not believe that Plato held a systematic “Theory of Forms” that could be thoroughly unpacked by discursive means (as is a typical modern view) and since I also believe that the second part of the Parmenides shows in practice the necessity for Forms, I see the Philebus not as rejecting Forms or developing a new mathematical approach to the One and the Many but rather as returning to an old problem that requires reexamination in a new way continuous with the concerns of Plato’s earlier works. The reason I need to treat the Philebus at this point (before coming explicitly to the Symposium and Phaedrus) is not only because of its clear connection with the Republic and the reappearance of Socrates but also because it is one of Plato’s most revolutionary works that shows, I think, a new way of reunderstanding the Republic.