The names of Plato and Aristotle tower above all others in Grecian philosophy. Many compositions from both have been preserved, though only a small proportion of the total number left by Aristotle. Such preservation must be accounted highly fortunate, when we read in Diogenes Laertius and others, the long list of works on various topics of philosophy, now irrecoverably lost, and known by little except their titles. Respecting a few of them, indeed, we obtain some partial indications from fragmentary extracts and comments of later critics. But none of these once celebrated philosophers, except Plato and Aristotle, can be fairly appreciated upon evidence furnished by themselves. The Platonic dialogues, besides the extraordinary genius which they display as compositions, bear thus an increased price (like the Sibylline books) as the scanty remnants of a lost philosophical literature, once immense and diversified. Under these two points of view, I trust that the copious analysis and commentary bestowed upon them in the present work will not be considered as unnecessarily lengthened. I maintain, full and undiminished, the catalogue of Plato's works as it was inherited from antiquity and recognised by all critics before the commencement of the present century. Yet since several subsequent critics have contested the canon, and set aside as spurious many of the dialogues contained in it,--I have devoted a chapter to this question, and to the vindication of the views on which I have proceeded. The title of these volumes will sufficiently indicate that I intend to describe, as far as evidence permits, the condition of Hellenic philosophy at Athens during the half century immediately following the death of Sokrates in 399 B.C. My first two chapters do indeed furnish a brief sketch of Pre-Sokratic philosophy: but I profess to take my departure from Sokrates himself, and these chapters are inserted mainly in order that the theories by which he found himself surrounded may not be altogether unknown. Both here, and in the sixty-ninth chapter of my History, I have done my best to throw light on the impressive and eccentric personality of Sokrates: a character original and unique, to whose peculiar mode of working on other minds I scarcely know a parallel in history. He was the generator, indirectly and through others, of a new and abundant crop of compositions--the "Sokratic dialogues": composed by many different authors, among whom Plato stands out as unquestionable coryphæus, yet amidst other names well deserving respectful mention as seconds, companions, or opponents. It is these Sokratic dialogues, and the various companions of Sokrates from whom they proceeded, that the present work is intended to exhibit. They form the dramatic manifestation of Hellenic philosophy--as contrasted with the formal and systematising, afterwards prominent in Aristotle.