Skeptics.
4. The same remarks apply mutatis mutandis to the Skeptics. The interest of such a writer as Sextus Empiricus in early philosophy is to show that skepticism went back to an early date—as far as Xenophanes, in fact. But what he tells us is often of value; for he frequently quotes early views as to knowledge and sensation in support of his thesis.
Neoplatonists.
5. Under this head we have chiefly to consider the commentators on Aristotle in so far as they are independent of the Theophrastean tradition. Their chief characteristic is what Simplicius calls εὐγνωμοσύνη, that is, a liberal spirit of interpretation, which makes all early philosophers agree with one another in upholding the doctrine of a Sensible and an Intelligible World. It is, however, to Simplicius more than any one else that we owe the preservation of the fragments. He had, of course, the library of the Academy at his disposal.
B.—DOXOGRAPHERS
The Doxographi graeci.
6. The Doxographi graeci of Professor Hermann Diels (1879) threw an entirely new light upon the filiation of the later sources; and we can only estimate justly the value of statements derived from these if we bear constantly in mind the results of his investigation. Here it will only be possible to give an outline which may help the reader to find his way in the Doxographi graeci itself.
The “Opinions” of Theophrastos
7. By the term doxographers we understand all those writers who relate the opinions of the Greek philosophers, and who derive their material, directly or indirectly, from the great work of Theophrastos, Φυσικῶν δοξῶν ιηʹ (Diog. v. 46). Of this work, one considerable chapter, that entitled Περὶ αἰσθήσεων, has been preserved (Dox. pp. 499-527). And Usener, following Brandis, further showed that there were important fragments of it contained in the commentary of Simplicius (sixth cent. A.D.) on the First Book of Aristotle’s Φυσικὴ ἀκρόασις (Usener, Analecta Theophrastea, pp. 25 sqq.). These extracts Simplicius seems to have borrowed in turn from Alexander of Aphrodisias (c. 200 A.D.); cf. Dox. p. 112 sqq. We thus possess a very considerable portion of the First Book, which dealt with the ἀρχαί as well as practically the whole of the last Book.