The history of Greek philosophy, whether conceived in this comprehensive sense or as an erudite investigation into matters of detail, is a province which the Germans have made peculiarly their own; and, among German scholars, Dr. Zeller is the one who has treated it with most success. My obligations to his great work are sufficiently shown by the copious references to it which occur throughout the following pages. It is in those instances--and they are, unfortunately, very numerous--where our knowledge of particular philosophers and of their opinions rests on fragmentary or second-hand information, that I have found his assistance most valuable. This has especially been the case with reference to the pre-Socratic schools, the minor successors of Socrates, the earlier Stoics, the Sceptics, and the later Pythagoreans. I must, however, guard against the supposition that my work is, in any respect, a popularisation or abridgment of Zeller’s. To popularise Zeller would, indeed, be an impertinence, for nothing can be more luminous and interesting than his style and general mode of exposition. Nor am I playing the part of a finder to a large telescope; for my point of view by no means coincides with that of the learned German historian. Thus, while my limits have obliged me to be content with a very summary treatment of many topics which he has discussed at length, there are others, and those, in my opinion, not the least important, to which he has given less space than will be found allotted to them here. On several questions, also, I have ventured to controvert his opinions, notably with reference to the Sophists, Socrates, Aristotle, and Plotinus. My general way of looking at the Greeks and their philosophy also differs from his. And the reasons which have led me to follow an independent course in this respect involve considerations of such interest and importance, that I shall take the liberty of specifying them in some detail.