 The difficulties of assessing Plato’s ethical thought are compounded by the fact that the metaphysical underpinnings seem to have changed during his long life. In the Socratic dialogues, there are no indications that the search for virtue and the human good goes beyond the human realm. This changes with the middle dialogues, which show a growing interest in an all-encompassing metaphysical grounding of knowledge, a development that leads to the positing of the ‘Forms’ as the true nature of all things, culminating in the Form of the Good as the transcendent principle of all goodness. Though the theory of the Forms is not confined to human values, but encompasses the whole of nature, Plato in the middle dialogues seems to assume no more than an analogy between human affairs and cosmic harmony. The late dialogues, by contrast, display a growing tendency to assume a unity between the microcosm of human life and the macrocosmic harmonic order of the entire universe, a tendency that is displayed most fully in the Philebus and the Timaeus. While these holistic tendencies appeal to the imagination because they rely on harmonic relations expressed in mathematical proportions, the metaphysical status of the Forms is even harder to make out in the late dialogues than in the middle dialogues. Though Plato’s late works do not show any willingness to lower the standards of knowledge as such, Plato acknowledges that his design of a rational cosmic order is based on conjecture and speculation, an acknowledgement that finds its counterpart in his more pragmatic treatment of ethical standards and political institutions in his latest politcal work, the Laws. Finally, at no stage of his philosophy does Plato go into a systematic treatment of, or and commitment to, basic principles of ethics from which rules and norms of human interaction can be derived and justified. Instead, Plato largely confines himself to the depiction of the good soul and of what is good for the soul, on the assumption that the state of the soul is the necessary and sufficient condition for the good life and its moral precepts. This abstemiousness explains the widely diverging reconstructions of Plato’s ethics in the secondary literature from antiquity to this day.