This volume marks the beginning of an enterprise undertaken on the initiative of the Syndics of the Cambridge University Press. They decided, first, that there was room for a comprehensive history of ancient Greek philosophy in English, on a considerable scale. The only such history available is the four-volume translation of Theodor Gomperz's Greek Thinkers, the last volume of which was finished by Gomperz in 1909. This was a valuable work for its time, though somewhat discursive, but a vast amount of detailed research has been carried out during the last half-century which has left no comer of the field untouched, and in some places has radically altered its contours.

Secondly, the Syndics took the view that the plan of a composite history by several hands, of which the Press has produced such notable examples in the past, had certain drawbacks, and that in this subject it would be preferable for the whole to be the product of a single mind.

Their third wish was that the work should not demand from its readers a knowledge of Greek.

I am well aware of the magnitude of the task, and of my temerity in accepting the proposal of the Syndics that I should undertake it. The difficulties are the reverse of those which beset a pioneer. Far from being a pioneer study, this history deals with a subject of which almost every detail has been minutely worked over many times. What is needed (and few would dispute the need) is a comprehensive and systematic account which will so far as possible do justice to the opposing views of reputable scholars, mediate between them, and give the most reasonable conclusions in a clear and readable form. The qualities called for are not originality and brilliance so much as clear-headedness, sober sense, good judgment and perseverance.

Yet to throw light on the Greek mind calls in addition for gifts of imagination, sympathy and insight. It means entering into the thoughts of men moulded by a civilization distant in time and place from our own who wrote and spoke in a different language.