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From, A History of Greek Philosophy, vol. I, The early Presocratics and the Pythagoreans, Cambridge University Press, 1962, pp. 1-25.
Page 29
To trace this whole story is not the work of one book, nor probably of one man. I mention the continuance of the Greek tradition in Christian philosophy because it is something that must not be forgotten, and constitutes one of the reasons for continuing to study ancient Greek thought today. But the present work will be confined to the non-Christian world, and that being so, I think it is best to make the break before the Neoplatonists rather than attempt to include them. With Plotinus and his followers, as well as with their Christian contemporaries, there does seem to enter a new religious spirit which is not fundamentally Greek (Plotinus himself was an Egyptian and his pupil Porphyry a Syrian who originally bore the name of Malchus), and points rather forward as a preparation for medieval philosophy than back to the ancient world.
One other point must be made clear before we start. In the course of this history I shall mention the names of a large number of philosophers and attempt to assess their achievement. Yet only of three or four of these do we possess any whole or connected writings. Plato's dialogues have come down to us entire. Of Aristotle we have a large amount of miscellaneous writings which are partly the notes for lectures and partly collections of material more or less worked up into scientific treatises on the subjects with which they deal. Within this corpus it is not always easy to be sure whether what we possess is from the pen of Aristotle himself or of one of his pupils, nor how far what is basically Aristotle's has been reworked and enlarged by pupils or editors. In addition to these manuscripts, which were intended for use within the school and have little pretension to literary merit, Aristotle left a number of published dialogues which were greatly admired in antiquity for their style as well as their content. These, however, are lost. We have some complete treatises of his successor Theophrastus. Of Epicurus, who was one of the most prolific writers of antiquity, we now possess only three philosophical letters to friends (of which one, though containing genuine sentiments of Epicurus, is probably not from his hand), a collection of forty 'Principal Doctrines' each a mere sentence or brief paragraph and some aphorisms.
For all the other major figures in Greek philosophy, including for example all the Presocratics, Socrates (who wrote nothing), and the Stoics not excepting Zeno himself, we are dependent on quotations and excerpts of varying lengths occurring in other authors, or paraphrases and accounts of their thought which often display a more or less obvious bias. This, the outstanding difficulty for a historian of Greek philosophy, must be appreciated at the outset. Except for Plato and Aristotle, the question of the nature and trustworthiness of our sources inevitably obtrudes itself at every turn.
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