Very little is known about Thales. He was considered to be one of the Seven Sages, which by itself is a testimony of his acumen. On the one hand, although many scientiﬁc achievements are attributed to him, such as discovering the cause of a solar eclipse, or proving some geometrical theorems, these achievements were reported 700 to 1000 years after his death. Early sources, on the other hand, supposedly indicate that he was primarily a practical man “with a bent towards natural science.”9
Although the doubts about Thales’ contribution to geometry and astronomy are justiﬁed, his theoretical bent is nevertheless very strong, which is manifested in his philosophy. Aristotle says that Thales is among “the wise (σoφoί) but not practically wise (φρόνιμοι)” (EN 1141b4–5 = 59A30), but, when pressed, Thales can show practical applications of his theoretical pursuits as exempliﬁed in the story of the olive-press scheme (Pol. 1259a6–23 = 11A10). Aristotle is the authority on Thales’ most famous statement that water is the arche of the universe where arche is “that of which all existing things are and from which they ﬁrst come to be and into which they are ﬁnally destroyed, its substance remaining, but changing in its properties” (Met. 983b6–11,17–27 = A12).10 Whether Thales himself would agree with such an absolutist understanding of the arche remains uncertain, but because Anaximander is credited with the ﬁrst use of arche and because such an absolutist understanding of the arche ﬁts in with what we know about Anaximander and Anaximenes, it seems reasonable that Thales understood it similarly. That is, everything that exists, according to this understanding of the arche, is but a manifestation of the eternal watery substrate and if everything perishes, one thing remains, namely water.11
Why did Thales choose water as the arche? Many answers have been conjectured. The reasons were already obscure for Aristotle, who says that Thales got the notion “perhaps from seeing that the nourishment of everything is moist” (A12). That is, one ingredient is present in all foods, namely water, and thus water must be a factor that makes nourishment nourishing.
9 D.R. Dicks, ‘Thales’, Classical Quarterly 53 (1959), p. 297.
10 It is clear that Aristotle did not have access to original writings of Thales (if there were such writings), but quotes from Hippias, as argued by Bruno Snell, ‘Die Nachrichten über die Lehren des Thales und die Anfänge der griechischen Philosophie- und Literaturgeschichte’, Philologus 96 (1944), pp. 170–182, and so Hippias is “at the beginning of writing on history of philosophy,” p. 181. Cf. Jaap Mansfeld, ‘Aristotle and others on Thales, or the beginning of natural philosophy’, Mnemosyne 38 (1985), p. 115.
11 It is “more than improbable” that Thales used the concept of arche, as stated by Wolfgang H. Pleger, Die Vorsokratiker (Stuttgart: Metzler, 1991), p. 58. But Thales could express the arche idea without mentioning the concept.