THALES OF MILETUS
(sixth century BCE)

Thales of Miletus is widely depicted in ancient sources as a pioneering rationalist and the founding father of Greek philosophy, science, and mathematics. Famous for ingenuity in many areas, he was also numbered among the seven sages (Sophoi or wise men). Evidence for his life and thought is meager and often questionable. Although written work is attested, nothing survives and he probably wrote nothing (Greek script still had limited uses). The earliest extant reports come from the historian Herodotus (c. 484–between 430 and 420 BCE); other evidence derives largely from Aristotle and his younger colleagues, Theophrastus and Eudemus (fourth century BCE). Hence, the reliability of the evidence depends heavily on the accuracy of the information available to them. Their testimony has been challenged by many scholars. But recent studies afford grounds for confidence, in part by tracing how Thales' ideas were transmitted by his intellectual heirs, including his younger compatriots Anaximander and Anaximenes.

Thales is a pivotal figure not unlike Galileo Galilei. Before him come cosmogonic verse (influenced by Near Eastern and Egyptian traditions) and a century of rapid advances in Greek culture, most notably in civic institutions and technology (e.g., building, coinage, and writing). In his wake, empirical inquiry, abstract speculation, and critical debate flower. Although his role in those developments cannot be assessed precisely, it was probably seminal. Early sources tell of travel to Egypt (where Miletus had a major trading depot), regional diplomacy (advocating a federation of Ionian cities to counter aggressive foreign neighbors), and diverse feats of engineering (diverting the course of the Halys River), economics (monopolizing olive presses), and surveying (calculating the height of pyramids and the distance of ships from shore).

Thales' significance for the history of philosophy stems mainly from his insights in three areas: cosmology, astronomy, and geometry. He is best known today for the bold but obscure claim that water is the archē (source or basic causal factor) of everything, ostensibly on the grounds that moisture (not water narrowly defined but fluid generally) is both the "seed" (originating source) and "food" (source of growth and sustenance) of all things. What exactly Thales said or meant is unrecoverable. Aristotle, the primary source for these claims, calls him the founder of material explanation: specifying the material constituents responsible for persistence and change. Thales also proposed that the earth floats on water "like wood"; and he attributed earthquakes to the earth's occasional rocking. Related considerations probably included the mobility of water, its exceptional mutability (readily solidifying and vaporizing), and its ubiquity (falling from the sky, emerging from springs, and both surrounding the land and filling its depressions).

Antiquity admired Thales most for his astronomy. Most famous was his alleged prediction of a solar eclipse (securely dated to May 28, 585 BCE) that halted a major foreign battle. The story, which many scholars doubt, appears first in Herodotus, who says only that he forecast the year. But a newly recovered text on papyrus cites the astronomer Aristarchus of Samos (flourished c. 270 BCE) crediting Thales with discovering the cause of solar eclipses by first determining that they occur only at a new moon. Other reports of his stargazing are more credible: charting the periodic rising and setting of prominent stars and star clusters (as in Hesiod's verse, over a century earlier); introduction of a circumpolar constellation (Ursa Minor); and a rough determination of the solstices and equinoxes, which enabled him to correlate the annual cycles of the sun and stars more reliably, thereby improving Greek calendrical schemes. Methodical observation of the horizon was the basis for most of these discoveries, but study of the lunar cycle is also reported.

Several new insights in geometry are ascribed to Thales: the equality of the opposite angles formed by intersecting lines; the equality of the base angles in isosceles triangles; the bisection of circles by their diameters; the congruence of triangles having a side and two angles equal; and the proportionality of similar triangles. The latter two are cited in connection with practical procedures: the former to calculate the distance of ships, the second to calculate the height of pyramids in Egypt. The novelty of his ideas probably lay not in simply enunciating these elementary propositions, nor in their formal proof, but in asserting their universal scope on the basis of ad hoc reasoning or evidence. Other innovative ideas attributed to Thales include the earliest recorded explanation for the Nile's annual flooding (seasonal winds obstruct its flow), a claim that amber and magnets are animate (because they cause motion, though curiously not self-motion), and a claim that all things are full of gods (perhaps because full of water, which exhibits two standard attributes of divinity: it is both deathless and life-giving). Implicit in many of the views attributed to Thales are basic principles of rational inquiry and naturalistic explanation: observation, analysis, abstraction, generalization, and regularity. Provided that some of this evidence is accurate, Thales may reasonably be counted as the first philosopher—well before the word was coined.

See also Anaximander; Anaximenes; Archē; Aristotle; Nomos and Phusis; Pre-Socratic Philosophy; Theophrastus.

Bibliography

texts and translations

Diels, Hermann, and Walther Kranz, eds. Die Fragmente der Vorsokratiker. 3 vols. 6th ed. Berlin: Weidmann, 1951–1952. The standard (but incomplete) collection of ancient testimony (widely cited as DK or VS ).

Kirk, Geoffrey S., J. E. Raven, and Malcolm Schofield. The Presocratic Philosophers. 2nd ed. New York: Cambridge University Press, 1983. A useful selection of texts with translation and judicious analysis.

studies

Mansfeld, Jaap. "Aristotle and Others on Thales, or The Beginnings of Natural Philosophy." Mnemosyne 40 (1987): 109–129. Analyzes Aristotle's testimony.

O'Grady, Patricia F. Thales of Miletus: The Beginnings of Western Science and Philosophy. Aldershot, U.K.: Ashgate, 2002. Suggestive but often uncritical discussion.

Panchenko, Dmitri. "Thales and the Origin of Theoretical Reasoning." Configurations 3 (1993): 387–414. An incisive case for his philosophical significance.

White, Stephen A. "Thales and the Stars." In Presocratic Philosophy, edited by Victor Caston and Daniel W. Graham. Aldershot, U.K.: Ashgate, 2002. A favorable reassessment of evidence for his astronomical study.

Stephen A. White (2005)