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(b. Miletus, Ionia, 625 B.C. [?] d. 547 B.C. [?])

natural philosophy.

Thales is considered by Aristotle to be the “founder” (ἀρχηγός) of Ionian natural philosophy.1 He was the son of Examyes and Cleobuline, who were, according to some authorities, of Phoenician origin. But the majority opinion considered him a true Milesian by descent (ἰυαγєνής Mιλήσιος), and of a distinguished family. This latter view is probably the correct one since his father’s name seems to be Carian rather than Semitic, and the Carians had at this time been almost completely assimilated by the Ionians. According to Diogenes Laèrtius, Apollodorus put Thales’ birth in Olympiad 35.1 (640 B.C.) and his death at the age of 78 in Olympiad 58 (548–545 B.C.). There is a discrepancy in the figures here; probably 35.1 is a mistake for 39.1 (624), since the confusion of є̄ and ῡ is a very common one. Apollodorus would in that case characteristically have made Thales’ death correspond with the date of the fall of Sardis, his floruit coincide with the eclipse of the sun dated at 585 B.C.–which he is alleged to have predicted–and assumed his birth to be the conventional forty years before his prime.2

Even in antiquity there was considerable doubt concerning Thales’ written works. It seems clear that Aristotle did not have access to any book by him, at least none on cosmological matters. Some authorities declare categorically that he left no book behind. Others, however, credit him with the authorship of a work on navigation entitled “The Nautical Star Guide,” but in spite of a tradition suggesting that Thales defined the Little Bear and recommended its navigational usefulness to Milesian sailors,3 it is extremely doubtful that he was the actual author of this work, since Diogenes Laërtius informs us that this book was also attributed to a certain Phokos of Samos. It is most unlikely that a work of Thales would have been ascribed to someone of comparative obscurity, but not the converse.

Much evidence of practical activities associated with Thales has survived, testifying to his versatility as statesman, tycoon, engineer, mathematician, and astronomer. In the century after his death he became an epitome of practical ingenuity.4 Herodotus records the stories that Thales advised the Ionians to establish a single deliberative chamber at Teos and that he diverted the river Halys so that Croesus’ army might be able to cross. (Herodotus is skeptical about the latter explanation.)5 Aristotle preserves another anecdote that credits Thales with considerable practical knowledge. According to this account, Thales, when reproached for his impracticality, used his skill in astronomy to forecast a glut in the olive crop, went out and cornered the market in the presses, and thereby made a large profit. Aristotle disbelieves the story and comments that this was a common commercial procedure that men attributed to Thales on account of his wisdom.6 Plato, on the other hand, whose purpose is to show that philosophy is above mere utilitarian considerations, tells the conflicting anecdote that Thales, while stargazing, fell into a well and was mocked by a pretty Thracian servant girl for trying to find out what was going on in the heavens when he could not even see what was at his feet.7 It is clear that these stories stem from separate traditions–the one seeking to represent the philosopher as an eminently practical man of affairs and the other as an unworldly dreamer.

Thales achieved his fame as a scientist for having predicted an eclipse of the sun. Herodotus, who is our oldest source for this story, tells us that the eclipse (which must have been total or very nearly so) occurred in the sixth year of the war between the Lydians under Alyattes and the Medes under Cyaxares, and that Thales predicted it to the Ionians, fixing as its term the year in which it actually took place.8 This eclipse is now generally agreed to have occurred on 28 May 585 B.C. (–584 by astronomical reckoning). It has been widely accepted that Thales was able to perform this striking astronomical feat by using the so-called “Babylonian saros,” a cycle of 223 lunar months (18 years, 10 days, 8 hours), after which eclipses both of the sun and moon repeat themselves with very little change. Neugebauer, however, has convincingly demonstrated that the “Babylonian saros” was, in fact, the invention of the English astronomer Edmond Halley in rather a weak moment.9 The Babylonians did not use cycles to predict solar eclipses but computed them from observations of the latitude of the moon made shortly before the expected syzygy. As Neugebauer says,

. . . there exists no cycle for solar eclipses visible at a given place; all modern cycles concern the earth as a whole. No Babylonian theory for predicting a solar eclipse existed at 600 B.C., as one can see from the very unsatisfactory situation 400 years later, nor did the Babylonians ever develop any theory which took the influence of geographical latitude into account.10

Accrodingly, it must be assumed that if Thales did predict the eclipse he made an extremely lucky guess and did not do so upon a scientific basis, since he had no conception of geographical latitude and no means of determining whether a solar eclipse would be visible in a particular locality. He could only have said that an eclipse was possible somewhere at some time in the (chronological) year that ended in 585 B.C. But a more likely explanation seems to be simply that Thales happened to be the savant around at the time when this striking astronomical phenomenon occurred and the assumption was made that as a savant he must have been able to predict it. There is a situation closely parallel to this one in the next century. In 468–467 B.C. a huge meteorite fell at Aegospotami. This event made a considerable impact, and two sources preserve the absurd report that the fall was predicted by Anaxagoras, who was the Ionian savant around at that time.11

The Greeks themselves claim to have derived their mathematics from Egypt.12 Eudemus, the author of the history of mathematics written as part of the systematization of knowledge that went on in the Lyceum, is more explicit. He tells us that it was “Thales who, after a visit to Egypt, first brought this study to Greece” and adds “not only did he make numerous discoveries himself, but he laid the foundations for many other discoveries on the part of his successors, attacking some problems with greater generality and others more empirically.” Proclus preserves for us some of the discoveries that Eudemus ascribed to Thales, namely, that the circle is bisected by its diameter,13 that the base angles of an isosceles triangle are equal,14 and that vertically opposed angles are equal.15 In addition he informs us that the theorem that two triangles are equal in every respect if they have two angles and one side respectively equal was referred by Eudemus to Thales with the comment that the latter’s measuring the distance of ships out at sea necessarily involved the use of this theorem.16

From the above it can be seen that Eudemus credited Thales with full knowledge of the theory behind his discoveries. He also held that Thales introduced geometry into Greece from Egypt. Our surviving sources of information about the nature of Egyptian mathematics, however, give us no evidence to suggest that Egyptian geometry had advanced beyond certain rule–of–thumb techniques of practical mensuration. Nowhere do we find any attempt to discover why these techniques worked, nor anything resembling a general and theoretical mathematics. It seems most unlikely, then, that the Greeks derived their mathematics from the Egyptians. But could Thales have been the founder of theoretical mathematics in Greece, as Eudemus claimed? Here again the answer must be negative. The first three discoveries attributed to him by the Peripatetic most probably represent “just the neatest abstract solutions of particular problems associated with Thales.”17 Heath points out that the first of these propositions is not even proved in Euclid.18 As for the last of them, Thales could very easily have made use of a primitive angle–measurer and solved the problem in one of several ways without necessarily formulating an explicit theory about the principles involved.

Van der Waerden, on the other hand, believes that Thales did develop a logical structure for geometry and introduced into this study the idea of proof.19 He also seeks to derive Greek mathematics from Babylon. This is a very doubtful standpoint. Although Babylonian mathematics, with its sexagesimal place–value system, had certainly developed beyond the primitive level reached by the Egyptians, here too we find nowhere any attempt at proof. Our evidence suggests that the Greeks were influenced by Babylonian mathematics, but that this influence occurred at a date considerably later than the sixth century B.C. If the Greeks had derived their mathematics from Babylonian sources, one would have expected them to have adopted the much more highly developed place-value system. Moreover, the Greeks themselves, who are extremely generous, indeed overgenerous, in acknowledging their scientific debts to other peoples, give no hint of a Babylonian source for their mathematics.

Our knowledge of Thales’ cosmology is virtually dependent on two passages in Aristotle. In the Metaphysics (A3, 983b6) Aristotle, who patently has no more information beyond what is given here, is of the opinion that Thales considered water to be the material constituent of things, and in the De caelo (B13, 294a28), where Aristotle expressly declares his information to be indirect, we are told that Thales held that the earth floats on water. Seneca provides the additional information (Naturales quaestiones, III , 14) that Thales used the idea of a floating earth to explain earthquakes. If we can trust this evidence, which seems to stemultimately from Theophrastus via a Posidonian source, the implication is that Thales displays an attitude of mind strikingly different from anything that had gone before. Homer and Hesiod had explained that earthquakes were due to the activity of the god Poseidon, who frequently bears the epic epithet “Earth Shaker,” Thales, by contrast, instead of invoking any such supernatural agency, employs a simple, natural explanation to account for this phenomenon. Cherniss, however, has claimed that Aristotle’s knowledge of Thales’ belief that the earth floats on water would have been sufficient to induce him to infer that Thales also held water to be his material substrate.20 But it is impossible to believe that Aristotle could have been so disingenuous as to make this inference and then make explicit conjectures as to why Thales held water to be his άpρχή. Aristotle’s conjectured reasons for the importance attached by Thales to water as the ultimate constituent of things are mainly physiological. He suggests that Thales might have been led to this conception by the observation that nutriment and semen are always moist and that the very warmth of life is a dampwarmth. Burnet has rejected these conjectures by Aristotle on the ground that in the sixth century interests were meteorological rather than physiological.21 But, as Baldry has pointed out, an interest in birth and other phenomena connected with sex is a regular feature even of primitive societies long before other aspects of biology are thought of.22 However this may be, it is noteworthy that, in view of the parallels to be found between Thales’ cosmology and certain Near Eastern mythological cosmogonies,23 there exists the possibility that Thales’ emphasis upon water and his theory that the earth floats on water were derived from some such source, and that he conceived of water as a “remote ancestor” rather than as a persistent substrate. But even it Thales was influenced by mythological precedents24 and failed to approximate to anything like the Aristotelian material cause, our evidence, sparse and controversial though it is, nevertheless seems sufficient to justify the claim that Thales was the first philosopher. This evidence suggests that Thales’ thought shared certain basic characteristics with that of his Ionian successors. These Milesian philosophers, abandoning mythopoeic forms of thought, sought to explain the world about them in terms of its visible constitutents. Natural explanations were introduced by them, which took the place of supernatural and mystical ones.25 Like their mythopoeic predecessors, the Milesians firmly believed that there was an orderliness inherent in the world around them. Again like their predecessors, they attempted to explain the world by showing how it had come to be what it is. But, instead of invoking the agency of supernatural powers, they sought for a unifying hypothesis to account for this order and, to a greater or lesser extent, proceeded to deduce their natural explanations of the various phenomena from it. Two elements, then, characterize early Greek philosophy, the search for natural as opposed to supernatural and mystical explanations, and secondly, the search for a unifying hypothesis. Both of these elements proved influential in paving the way for the development of the sciences, and it is in the light of this innovation that Thales’s true importance in the history of science must be assessed.


1.Metaphysics, A3, 983b17 ff. (DK, 11A12).

2. These datings are now approximately in accordance with the figures given by Demetrius of Phalerum, who placed the canonization of the Seven Sages (of whom Thales was universally regarded as a member) in the archonship of Damasias at Athens (582–581 B.C.).

3. Callimachus, Iambus, 1, 52 f. 191 Pfeiffer (DK, 11A3a).

4. See Aristophanes, Birds 1009; Clouds 180.

5. Herodotus, I, 170; I, 75 (DK, 11A4, 11A6).

6.Politics, A11, 1259a6 (DK, 11A10).

7.Theaetetus, 174A (DK, 11A9). It is odd that Plato should have applied this story to someone as notoriously practical in his interests as Thales. It makes one think that there may be at least a grain of truth in the story. See my review of Moraux’s Budé edition of the De caelo, in Classical Review, n.s., 20 (1970), 174, and M. Landmann and J. O. Fleckenstein, “Tagesbeobachtung von Sternen in Altertum.” in Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich, 88 (1943), 98, notwithstanding Dicks’ scornful dismissal of their suggestion. Certainly the motive for this story is clear, but it could have been Thales’ practice that determined its form. In general Dicks is far too skeptical in his treatment of the stories told of Thales and relegates them to the status of “the famous story of the First World War about the Russians marching through England with ‘snow on their boots.’” But on this latter story see Margo Lawrence, Shadow of Swords (London, 1971), in which she reveals that soldiers from Russia, wearing Russian uniform, carrying balalaikas, and singing Slavonic songs, did in fact disembark in 1916 at Newcastle upon Tyne. Admittedly the snow on their boots must be left to folklore.

8. I, 74 (DK, 11A5).

9. O. Neugebauer, The Exact Sciences in Antiquity, 141.

10.Ibid., 142.

11. See Diogenes Laërtius, II, 10 (DK, 59A1), and Pliny, Historia naturalis, II , 149 (DK, 59A11), See also Cicero, Dedivinatione, I .50.112 (DK, 12A5a), and Pliny, ibid., II , 191, for a sixth–century parallel, where Anaximander is alleged to have predicted an earthquake.

12. See Herodotus, II , 109, who believes that geometry originated from the recurrent need to remeasure land periodically flooded by the Nile: Aristotle, Metaphysics, A3, 98Ib20–25, who believes that mathematics evolved in a highly theoretical way as the invention of a leisured class of Egyptian priests: and Eudemus, who, in spite of being a Peripatetic, sides with Herodotus rather than with Aristotle (see Proclus, Commentary on Euclid’s Elements, I, 64, 16 “Friedlein”)

13.Commentary on Euclid’s Elements, 157.10 (DK, 11A20)

14.Ibid., 250.20.

15.Ibid., 299.1.

16.Ibid., 352.14.

17. G. S. Kirk, The Presocratic Philosophers, 84.

18. T. L. Heath, Greek Mathematics, I , 131.

19. B. L. van der Waerden, Science Awakening, 89.

20. H. Cherniss, “The Characteristics and Effects of Presocratic Philosophy,” in Journal of the History of Ideas, 12 (1951), 321.

21. J. Burnet, Early Greek Philosophy, 48.

22. H. C. Baldry, “Embryological Analogies in Early Greek Philosophy,” in Classical Quarterly, 26 (1932), 28.

23. For an excellent account of Egyptian and Mesopotamian cosmogonies, see H. Frankfort, ed., Before Philosophy (Penguin Books, London, 1949), pub. orig. as The Intellectual Adventure of Ancient Man (Chicago, 1946).

24. Aristotle, it may be noted, cites the parallel in Greek mythology of Oceanus and Tethys, the parents of generation (Metaphysics, A3, 983b27ff. [DK,1B10]). But the Greek myth may itself be derived from an oriental source.

25. The gods of whom Thales thought everything was full (see Aristotle. De anima, A5, 411a7 [DK, 11A22]) are manifestly different from the personal divinities of traditional mythology.


For a collection of sources see H. Diels and W. Kranz, Die Fragmente der Vorsokratiker, 6th ed., 3 vols, (Berlin, 1951–1952), I , 67–79 (abbreviated as DK above).

See also H. C. Baldry, “Embryological Analogies in Presocratic Cosmogony,” in Classical Quarterly, 26 (1932), 27–34; J. Burnet, Greek Philosophy: Part I , Thales to Plato (London, 1914); and Early Greek Philosophy, 4th ed, (London, 1930); H . Cherniss, “The Characteristics and effects of Presocratic Philosophy,” in Journal of the History of Ideas, 12 (1951), 319–345; D. R. Dicks, “Thales,” in Classical Quarterly, n.s. 9 (1959), 294–309; and “Solstices, Equinoxes and the Presocratics,” in Journal of Hellenic Studies, 86 (1966), 26–40; J. L. E. Dreyer, A History of the Planetary Systems from Thales to Kepler (Cambridge, 1906), repr, as A History of Astronomy from Thales to Kepler (New York, 1953); W. K. C. Guthrie, A History of Greek Philosophy, I (Cambridge, 1962); T. L. Heath, Aristarchus of Samos (Oxford, 1913); and Greek Mathematics, I (Oxford, 1921); U. Hölscher, “Anaximander und die Anfänge der Philosophie,” in Hermes, 81 (1953), 257–277, 385–417; repr. in English in Allen and Furley, Studies in Presocratic Philosophy, I (New York, 1970), 281–322; C. H. Kahn, “On Early Greek Astronomy,” in Journal of Hellenic Studies, 90 (1970), 99–116; G. S. Kirk and J. E. Raven, The Presocratic Philosophers (Cambridge, 1957); O. Neugebauer, “The History of Ancient Astronomy, Problems and Methods,” in Journal of Near Eastern Studies, 4 (1945), 1–38; The Exact Sciences in Antiquity (Princeton, 1952; 2nd ed., Providence, R.I., 1957); and “The Survival of Babylonian Methods in the Exact Sciences of Antiquity and Middle Ages,“in Proceedings of the American Philosophical Society, 107 (1963), 528–535; and B. L. van der Waerden, Science Awakening, Arnold Dresden, trans. (Groningen, 1954).

James Longrigg

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c. 625 b.c.e.–c. 547 b.c.e.


The Founder of Greek Philosophy.

The Greeks looked upon Thales as the founder of Greek philosophy and the first man to attempt to provide a scientific explanation for the origin of the world. He was born in Miletus on the south-west coast of Asia Minor around 625 b.c.e. and in his youth he was an avid traveler. As Hieronymus of Rhodes indicates in his report, Thales measured the pyramids by their shadow, having observed the time when a person's shadow is equal to the person's height. It wasn't long after his trip to Egypt that Thales went to Greece to further his study of geometry. It was in Greece that he began to lecture on natural sciences and philosophy and he founded one of the first Greek schools of philosophy the Ionian School, also called the Milesian school.

Legend of Eclipse Prediction.

Thales was said to have predicted an eclipse of the sun which has traditionally been dated to 585 or 584 b.c.e. and if this report is true, it would provide the one certain date in his life. Whether he actually predicted the eclipse or not is a matter of dispute. At one time scholars believed that he used astronomical observations borrowed from Babylon to make his prediction, but it is now known that at this time, the Babylonians had no theory for predicting solar eclipses that Thales could have used. Moreover, the story goes that the eclipse that Thales predicted took place just as the Medes and the Lydians were about to fight a battle at the Halys River in Asia Minor, and the Milesians were present as allies of Lydia. The eclipse caused the Medes and Lydians to break off the battle. The story implies that the eclipse took place during daylight hours, and there was no solar eclipse at a suitable hour in 585 or 584 b.c.e., though on 21 September 582, there was a partial eclipse, three-quarters total at 10 and this may have been the eclipse which Thales was said to have foretold. Clearly Thales' prediction was a legend, but it is evidence of his reputation as an astronomer was among the Greeks.

Anecdotes about Thales.

There were a number of similar stories told of Thales' activities as engineer, mathematician, and astronomer, as well as a philosopher. When his critics derided his wisdom as impractical, he used his astronomical knowledge to predict a superabundant crop of olives, and made a fortune by cornering the market in olive presses. Another story which presented him as an absent-minded intellectual told that while he was stargazing, he fell into a well, and a servant girl who found him laughed at him because he failed to notice what was at his feet as he examined the heavens. He discovered that two triangles were equal if two angles and one side were equal and he evidently used this theorem to measure the distance of ships out at sea. He was credited with a book on navigation titled the Nautical Star Guide, but it is doubtful if he was the author of this work. Most scholars think that Thales wrote nothing.

Contribution to Natural Philosophy.

Thales argued that the material constituent of all things is water. The earth, he claimed, floats on water, and he used this theory to explain why earthquakes occurred. He rejected the explanation that they took place when a god such as Poseidon shook the earth. It is possible that he derived his theory from Near Eastern mythological explanations of creation, for Babylonian descriptions of the world order spoke of the "waters under the earth." Yet Thales' doctrine did not turn to supernatural or mystical explanations in order to understand natural phenomena. Instead of elaborating stories of how the universe came into existence, as Hesiod did in his Theogony which proposed a theological explanation for how the world arose from chaos, Thales posed a new question—"What is the universe?—and his answer was a theory based on observation of the real world. As such he paved the way for the development of modern natural science.

Helped Croesus During War With Persia.

When Thales was an old man, the Lydian kingdom, then ruled by Croesus, whose wealth was proverbial, was threatened by a new enemy, Cyrus, king of Persia, who had overthrown the last king of the Medes in 550 b.c.e. Croesus, whose sister had married the last king of the Medes, wondered if he should attack Persia before it grew too strong, and he consulted the oracle of Apollo at Delphi. The oracle gave the ambiguous answer, "If Croesus crosses the Halys River, a great empire will fall." Croesus imagined the prophecy was favorable and launched an attack, not realizing that his empire was the one destined to fall. Thales accompanied him, and another legend told that he helped the Lydians cross the Halys River by diverting part of the stream into another channel. Croesus was defeated, and in 547 or 546 b.c.e. his capital of Sardis fell to Cyrus. The Ionian cities that had been subject to Croesus wondered what to do, and Thales proposed that they should form a federal state and present a united front to Persia. But Cyrus split the Ionian resistance by offering Miletus a favorable alliance and leaving the conquest of the rest of Ionia to one of his generals. Following this event, Thales passed from the historical records until his death around 547 b.c.e.


Robert S. Brumbaugh, The Philosophers of Greece (New York: Thomas Y. Crowell, 1964).

John Burnet, Greek Philosophy; Thales to Plato (London, England: Macmillan, 1950).

James Longrigg, "Thales," in Dictionary of Scientific Biography. Vol. XIII. Ed. Charles Coulson Gillespie (New York: Charles Scribers Sons, 1976): 295–298.

Erwin Schrödinger, Nature and the Greeks (Cambridge: Cambridge University Press, 1954).

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The Greek natural philosopher Thales (ca. 624-ca. 545 B.C.) founded the Ionian school of ancient Greek thinkers.

Thales was descended, according to the historian Herodotus, from Phoenicians who had settled in Miletus, a thriving Greek seaport on the west coast of Asia Minor (now Turkey). His mother, however, bore a Greek name. Thales's interest in the heavens was so well known that the philosopher Plato picked him as the example of the impractical student: while gazing upward and scanning the stars, he fell into a well.

Thales became so famous for his practical shrewdness and theoretical wisdom that in later times he began to be honored for having made important discoveries whose true origins were not known then and in some cases are still obscure. The most spectacular of these supposed achievements was his alleged prediction of a total solar eclipse (presumably that of May 28, 585 B.C.), at a time when the information needed to foresee such an event was not yet possessed by anybody. Indeed it is significant that, according to Herodotus, the time mentioned in Thales's prediction was limited only to "the year in which the eclipse occurred." Month and day were not specified, nor was there any indication of the portion of the earth's surface from which the eclipse would be visible.

Thales was also falsely credited with having found out that an eclipse of the sun is caused by the interposition of the opaque moon between the sun and the earth. However, the real nature of the moon as a dark, non-self-luminous body was first disclosed about a century after the death of Thales. In like manner he was praised for having determined the sun's apparent diameter, yet this approximately correct value was first ascertained, according to the mathematician Archimedes, some 300 years after Thales by an accomplished astronomer.

The first proof that a circle is bisected by its diameter was ascribed in antiquity to Thales. But in his lifetime the Greeks had not yet begun to enunciate geometrical theorems and to demonstrate them step by step. Hence, the ancient attribution to Thales of the earliest proof of the equality of the vertical angles formed by the intersection of two straight lines is now discarded as a misplaced anticipation of a later stage in the development of Greek geometry.

In assigning to Thales the belief that "everything is full of gods, " Aristotle suggested that the Milesian perhaps derived this opinion from those who held that soul pervades the entire universe. With regard to Thales's conception of soul, Aristotle remarked that "on the basis of what people remember, Thales apparently assumed that soul causes motion, if he really said that the magnet has a soul since it attracts iron." Evidently Aristotle did not have in his hands the writings later ascribed to Thales. It is, in fact, entirely doubtful that Thales set his ideas down in written form.

In Aristotle's time the oldest traditional explanation of what held the earth up was that it rested on water. "They say that Thales the Milesian espoused this view, " Aristotle states, "because the earth remains afloat like wood or some other such thing." Aristotle wryly adds: "as though the same reasoning with regard to the earth did not apply also to the water supporting the earth." Thales based his conception of water as the fundamental principle of the universe, according to Aristotle's surmise, "on the observation that the nourishment of all things was moist, and that heat itself arises from this source and is kept alive by it." As a biologist, Aristotle appended the further reason that "the seeds of all things have a moist nature, " and one of his commentators contributed the remark that "dead things dry up."

The concept of the primacy of water may have been imported by Thales from the Egyptians, "who express this idea in mythical form." Whether or not Thales was familiar with the Egyptian water myths or the similar Mesopotamian stories and the corresponding notions in the Hebrew Bible, the framework of his thought was confined to the world of nature. Even though he overestimated the importance of water, its absence from the surface of the moon in part explains the nonexistence of life on this natural satellite. After the accomplishments actually due to Thales's successors have been stripped away from his previously exaggerated reputation, through the mists of early intellectual history Thales is dimly glimpsed as having turned rational thought to the demythologized understanding of the physical universe.

Further Reading

Modern discussions of Thales are necessarily limited by the fact that nothing of his has survived, and what may be gleaned from the writings of others is too little to permit the reconstruction of his thought. Nevertheless, G. S. Kirk and J. E. Raven present what is known about him in The Presocratic Philosophers (1964), as do John Burnet in Early Greek Philosophy (4th ed. 1930) and Kathleen Freeman in The Presocratic Philosophers (1953). Thales and his position in the development of Greek thought are also discussed in George Sarton, The Study of the History of Science (1936), and in Albin Lesky, A History of Greek Literature (1966). □

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Circa 625-Circa547 b.c.e



Mystery. Thales of Miletus lived and worked in the prosperous port city of Miletus on the coast of Asia Minor. Tradition credits him with a variety of ingenious solutions to practical problems, but Thales left no writings to posterity. Much of what is known about him comes from Aristotle, who regarded him as the first real phusiologos or natural scientist. Thales held that water was the basic building block of all matter.

Achievements. Thales allegedly visited Egypt, where he is supposed to have learned geometry, studied the rise and fall of the Nile, and determined the height of pyramids by measuring their shadows. He is said to have designed a canal that split the deep Lydian river Halys in two, diverting some of its flow into another channel so that the army of Croesus could safely cross it. His prediction of a solar eclipse in the year 585 b.c.e. was well known in the ancient world. When mocked on account of his poverty, he is said to have noted by observing the stars that there would be a large crop of olives at the next harvest. Thales then borrowed money from friends and used it to buy up all the olive presses in Miletus. When harvest arrived and the demand for presses was high, he rented them out at many times their original purchase price and thus made a large profit. Aristotle, who tells this story, states that it proves that philosophers could be rich if they wanted to, but they are not really interested in money.


G. E. R. Lloyd, Early Greek Science: Thales to Aristotle (New York: Norton, 1970).

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Thales (thā´lēz), c.636–c.546 BC, pre-Socratic Greek philosopher of Miletus and reputed founder of the Milesian school of philosophy. He is the first recorded Western philosopher. Thales taught that everything in nature is composed of one basic stuff, which he thought to be water. Prior to Thales, mythology had been used to explain the nature of the physical world; the significance of Thales thus lies not in his answer but in his approach. Although he apparently wrote nothing, he is believed to have introduced geometry into Greece and to have been a capable astronomer. It is said he predicted an eclipse of the sun in 585 BC Thales studied practical as well as speculative problems and was acknowledged one of the Seven Wise Men of Greece for his exhortation to unity among the Ionian Greeks.

See G. S. Kirk and J. E. Raven, The Presocratic Philosophers (1957).

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Thales (c.624–c.545 bc), Greek philosopher, mathematician, and astronomer, living at Miletus. One of the Seven Sages listed by Plato and judged by Aristotle to be the founder of physical science, he is also credited with founding geometry. He proposed that water was the primary substance from which all things were derived.

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Thales (c.636–c.546 bc) First Greek scientist and philosopher of whom we have any knowledge. He made discoveries in geometry, such as the angles at the base of an isosceles triangle are equal. Thales predicted the eclipse of the Sun that took place in 585 bc.