Thales’ activity is situated at Miletus between the second half of the seventh century and the first decades of the sixth century BC. He is included in the canonical list of the seven “Sages,” which goes back to an early date (P1b, cf. R2–R4). Histories of philosophy often present him as “the first philosopher,” largely because of the way in which Aristotle introduces him in the Metaphysics, as the first to have practiced a philosophy of “nature” (R9). But the most ancient testimonia, notably those of Aristophanes and Herodotus, rather suggest a multifaceted figure engaged above all in politics and (especially hydraulic) engineering. It is most likely that he left no writings behind, as is suggested by the fact that already Aristotle seems to have no direct knowledge of his ideas. A large number of mathematical and scientific discoveries are attributed to him by later authors, but it is usually difficult or impossible to say whether, and if so to what extent, they really do go back to him; in any case, we have put all these reports into the section on Thales’ reception (R13–R31). In general, the distinction, maintained here as in the other chapters, between doctrine and reception is more hypothetical in the case of Thales than in most other ones.