  In all likelihood, Plato wrote different dialogues at different times. We typically divide his writings into three periods. In the early ‘Socratic’ period, we find Apology, Crito, Euthyphro, Charmides, Ion, Lysis, Laches, Hippias Minor, Menexenus, Euthydemus and the Protagoras. The Hippias Major, Gorgias and perhaps the Meno belong to the end of this period, maybe with the Gorgias and more likely the Meno verging into the middle period. The middle period works include the Cratylus, Symposium, Phaedo, Republic and perhaps the Phaedrus. In the post-Republic phase we then find the Parmenides, Theaetetus, Sophist, Politicus, Timaeus, Philebus and Laws, along with the  Critias.[1]  The Socratic dialogues, so-called because Socrates is always the chief interlocutor, are thought to present doctrines of Socrates himself. These are dialogues devoted to ethical inquiries into the virtues, e.g., what is courage, or what is justice? In contrast, the middle period dialogues are thought to present the views of Plato, though nonetheless Socrates remains the speaker. Here for the first time we find remarks about the immortality of the soul, about special entities called ‘Forms’ that exist outside of space and time and that are both the objects of knowledge and somehow the cause of whatever transpires in the physical world, and the doctrine of recollection, the thesis that the immortal soul, in a disembodied state prior to its incarceration in a body, viewed these Forms, knowledge of which is then recalled by incarcerated souls through a laborious process. Socrates, in the early Apology, is non-committal about the immortality of the soul. Similarly, in the early dialogues we find that Socrates, in keeping with the claim that he is neither a metaphysician nor epistemologist, has nothing to say about recollection and never explicitly appeals to Forms. It is thus in the middle period works that one locates Plato's first thoughts about epistemological and metaphysical issues. To those topics we shall turn shortly. But these are, in the eyes of many, just first thoughts; for the dialogues in the late period suggest changes to key ethical, epistemological and metaphysical doctrines found in these middle period works. Over the course of the last fifty years, scholars have debated whether and to what extent Plato changed his views. The debate has grown so involved that it is perhaps best not to worry whether anyone believes the extreme positions that, on the one hand, Plato conceived of every one of his major doctrines before he ever wrote, or, on the other hand, that he changed his mind on central theses from one dialogue to the next. Broadly speaking, those who maintain that Plato keeps to his central theses from one period to the next are  Unitarians (see, for instance, Shorey 1903).  Those who believe that he changes his views from one period to the next are  Developmentalists (see, for instance, Owen 1986a).  The most plausible position, and the perhaps the dominant position in the contemporary scholarship, is somewhere in the middle. About some theses, Plato, over the course of his writings, expands his thoughts, recognizes difficulties, and even changes his mind. About other theses he stands by his fundamental insights.