Studies of Platös metaphysics have tended to emphasise either the radical change between the early Theory of Forms and the late doctrines of the Timaeus and the Sophist, or to insist on a unity of approach that is unchanged throughout Platös career. Professor Prior seeks to lay out an alternative approach. Focussing on two metaphysical doctrines of central importance to Platös thought ¿ the Theory of Forms and the doctrine of Being and Becoming ¿ he suggests a continuous progress can be traced through Platös works. He presents his argument through an examination of the metaphysical sections of six of the dialogues: the Euthyphro, Phaedo, Republic, Parmenides, Timaeus, and Sophist.