Critical discussion implies more than familiarity with other views, and more than mere disagreement with other theories. It is the adoption, or in this case, the development, of a new style of discussion. It is a procedure which encourages questioning, debate, explanation, justification and criticism. There was a unique relationship between the three Milesians and it is highly probable that the critical method developed in the Milesian School under the leadership of Thales.
Thales is the first person about whom we know to propose explanations of natural phenomena which were materialistic rather than mythological or theological. His theories were new, bold, exciting, comprehensible, and possible of explanation. He did not speak in riddles as did Heraclitus, and had no need to invent an undefined non-substance, as Anaximander did. Because he gave no role to mythical beings, Thales's theories could be refuted. Arguments could be put forward in attempts to discredit them. Thales's hypotheses were rational and scientific. Aristotle acknowledged Thales as the first philosopher, and criticized his hypotheses in a scientific manner.
The most outstanding aspects of Thales's heritage are: The search for knowledge for its own sake; the development of the scientific method; the adoption of practical methods and their development into general principles; his curiosity and conjectural approach to the questions of natural phenomena - In the sixth century B.C.E., Thales asked the question, 'What is the basic material of the cosmos?' The answer is yet to be discovered.
The Histories:They were still warring with equal success, when it happened, at an encounter which occurred in the sixth year, that during the battle the day was suddenly turned to night. Thales of Miletus had foretold this loss of daylight to the Ionians, fixing it within the year in which the change did indeed happen.1
1 All evidence, historical and astronomical, fixes the date of this eclipse as May 28, 585 B.C. There was another eclipse of the sun in Alyattes' reign, on Sept. 30, 610; but it appears that this latter was not total in Asia Minor: and Pliny's mention of the phenomenon places it in the 170th year from the foundation of Rome. Thales died at an advanced age in 548 B.C.
(The Histories, II.156) (Hdt. I.75)Hdt. V.52).(Hdt. II.97).Hdt. II.178, Strab. 17.1.18(Hdt. I.30)Hdt. V.53)
Theaetetus (174 A) Plato
Protagoras, 342 E-343 A).
Respublica , 600 A).
(Pl. Prt. 343 A-B)
Politic: [1259a]  and Apollodorus1 of Lemnos have written about both agriculture and fruit-farming, and similarly others also on other topics, so these subjects may be studied from these authors by anybody concerned to do so; but in addition a collection ought also to be made2 of the scattered accounts of methods that have brought success in business to certain individuals. All these methods are serviceable for those who value wealth-getting, for example the plan of Thales3 of Miletus, which is a device for the business of getting wealth, but which, though it is attributed to him because of his wisdom, is really of universal application. Thales, so the story goes, because of his poverty was taunted with the uselessness of philosophy; but from his knowledge of astronomy he had observed while it was still winter that there was going to be a large crop of olives, so he raised a small sum of money and paid round deposits for the whole of the olive-presses in Miletus and Chios, which he hired at a low rent as nobody was running him up; and when the season arrived, there was a sudden demand for a number of presses at the same time, and by letting them out on what terms he liked he realized a large sum of money, so proving that it is easy for philosophers to be rich if they choose, but this is not what they care about. Thales then is reported to have thus displayed his wisdom, but as  a matter of fact this device of taking an opportunity to secure a monopoly is a universal principle of business; hence even some states have recourse to this plan as a method of raising revenue when short of funds: they introduce a monopoly of marketable goods. There was a man in Sicily who used a sum of money deposited with him to buy up all the iron from the iron mines, and afterwards when the dealers came from the trading-centers he was the only seller, though he did not greatly raise the price, but all the same he made a profit of a hundred talents4 on his capital of fifty. When Dionysius5 came to know of it he ordered the man to take his money with him but clear out of Syracuse on the spot,6 since he was inventing means of profit detrimental to the tyrant's own affairs. Yet really this device is the same as the discovery of Thales, for both men alike contrived to secure themselves a monopoly. An acquaintance with these devices is also serviceable for statesmen, for many states need financial aid and modes of revenue like those described, just as a household may, but in greater degree; hence some statesmen even devote their political activity exclusively to finance. And since, as we saw,7 the science of household management has three divisions, one the relation of master to slave, of which we have spoken before,8 one the paternal relation, and the third the conjugal9—for it is a part of the household science to rule over wife and children （over both as over freemen, yet not with the same mode of government, but over the wife to exercise republican government and over the children monarchical）;
1 Also mentioned by Varro and Pliny.
2 The author of the Second Book of the pseudo-Aristotelian Oeconomica seems to have taken the hint.
3 The founder of Greek philosophy and mathematics, and one of the Seven Sages, 6th-5th cent. B.C.
4 The talent was about 240 pounds.
5 Dionysius the elder, tyrant of Syracuse 405-367 B.C.
6 cf. Thucydides οἱ δ᾽ οὐκέτι ἔμειναν ἀλλὰ . . .
7 2 init.
8 3 fin., 4.
9 The construction of the sentence is interrupted, and never completed.
Metaphysics:"Yet they do not all agree as to the number and the nature of these principles. Thales, the founder of this type of philosophy, says the principle is water (for which reason he declared that the earth rests on water), getting the notion perhaps from seeing that the nutriment of all things is moist, and that heat itself is generated from the moist and kept alive by it (and that from which they come to be is a principle of all things). He got his notion from this fact, and from the fact that the seeds of all things have a moist nature, and that water is the origin of the nature of moist things.
Aristotle, De Anima, 411a7. For other ancient sources see the discussion in Kirk and Raven, The Presocratic Philosophers, 93-7.
Thales would have recognized evaporation, and have been familiar with traditional views, such as the nutritive capacity of mist and ancient theories about spontaneous generation, phenomena which he may have 'observed', just as Aristotle believed he, himself had (Hist. An. 569 b1; Gen. An. 762 a9-763 a34), and about which Diodorus Siculus (I.7.3-5; 1.10.6), Epicurus (ap. Censorinus, D.N. IV.9), Lucretius (De Rerum Natura , V.783-808) and Ovid (Met. I.416-437) wrote.
In De Caelo Aristotle wrote: 'This [opinion that the earth rests on water] is the most ancient explanation which has come down to us, and is attributed to Thales of Miletus (Cael. 294 a28-30). He explained his theory by adding the analogy that the earth is at rest because it is of the nature of wood and similar substances which have the capacity to float on water, although not on air (Cael. 294 a30-b1). In Metaphysics (983 b21) Aristotle stated, quite unequivocally: 'Thales . . . declared that the earth rests on water'. This concept does appear to be at odds with natural expectations, and Aristotle expressed his difficulty with Thales's theory (Cael. 294 a33-294 b6).
An. Post. 94 a27-33; Metaph. 1051 a28).Arist. Metaph. 983 b20)
Thales's reputation for wisdom is further enhanced in a story which was related by Aristotle. (Politics, 1259 a 6-23). Somehow, through observation of the heavenly bodies, Thales concluded that there would be a bumper crop of olives. He raised the money to put a deposit on the olive presses of Miletus and Chios, so that when the harvest was ready, he was able to let them out at a rate which brought him considerable profit. In this way, Thales answered those who reproached him for his poverty. As Aristotle points out, the scheme has universal application, being nothing more than a monopoly. There need not have been a bumper harvest for the scheme to have been successful. It is quite likely that Thales was involved in commercial ventures, possibly the export of olive oil, and Plutarch reported that Thales was said to have engaged in trade (Plut. Vit. Sol. II.4).
History of geometry
as far as i can tell he doesn't specifically mention thales but rather improved upon thales theory
Aëtius attributed to Thales the concept that 'even the very fire of the sun and the stars, and indeed the cosmos itself is nourished by evaporation of the waters' (Aëtius, Placita, I.3).(Aët. III. 9-10)
Aëtius recorded that Thales and Democritus found in water the cause of earthquakes (Aët. III.15), and Seneca attributed to Thales a theory that on the occasions when the earth is said to quake it is fluctuating because of the roughness of oceans (QNat. III.14; 6.6). Although the theory is wrong, Thales's hypothesis is rational because it provides an explanation which does not invoke hidden entities. It is an advance upon the traditional Homeric view that they resulted from an angry supernatural god, Poseidon, shaking the earth through his rapid striding Aëtius (II.28)
De natura Deorum, i.,10
Seneca, QNat., Quaestiones Naturales(Sen. QNat. III.14).
(Sen. QNat., III.25. 7-10)
The Natural History: CHAP. 9. (12.)—AN ACCOUNT OF THE OBSERVATIONS THAT HAVE BEEN MADE ON THE HEAVENS BY DIFFERENT INDIVIDUALS. The first among the Romans, who explained to the people at large the cause of the two kinds of eclipses, was Sulpicius Gallus, who was consul along with Marcellus; and when he was only a military tribune he relieved the army from great anxiety the day before king Perseus was conquered by Paulus1; for he was brought by the general into a public assembly, in order to predict the eclipse, of which he afterwards gave an account in a separate treatise. Among the Greeks, Thales the Milesian first investigated the subject, in the fourth year of the forty-eighth olympiad, predicting the eclipse of the sun which took place in the reign of Alyattes, in the 170th year of the City2. After them Hipparchus calculated the course of both these stars for the term of 600 years3, including the months, days, and hours, the situation of the different places and the aspects adapted to each of them; all this has been confirmed by experience, and could only be acquired by partaking, as it were, in the councils of nature. These were indeed great men, superior to ordinary mortals, who having discovered the laws of these divine bodies, relieved the miserable mind of man from the fear which he had of eclipses, as foretelling some dreadful events or the destruction of the stars. This alarm is freely acknowledged in the sublime strains of Stesichorus and Pindar, as being produced by an eclipse of the sun4. And with respect to the eclipse of the moon, mortals impute it to witchcraft, and therefore endeavour to aid her by producing discordant sounds. In consequence of this kind of terror it was that Nicias, the general of the Athenians, being ignorant of the cause, was afraid to lead out the fleet, and brought great distress on his troops5. Hail to your genius, ye interpreters of heaven! ye who comprehend the nature of things, and who have discovered a mode of reasoning by which ye have conquered both gods and men6! For who is there, in observing these things and seeing the labours7 which the stars are compelled to undergo (since we have chosen to apply this term to them), that would not cheerfully submit to his fate, as one born to die? I shall now, in a brief and summary manner, touch on those points in which we are agreed, giving the reasons where it is necessary to do so; for this is not a work of profound argument, nor is it less wonderful to be able to suggest a probable cause for everything, than to give a complete account of a few of them only.
1 This eclipse is calculated to have occurred on the 28th of June, 168 B.C.; Brewster's Encyc. "Chronology," p. 415, 424. We have an account of this transaction in Livy, xliv. 37, and in Plutarch, Life of Paulus Æmilius, Langhorne's trans. ii. 279; he however does not mention the name of Gallus. See also Val. Maximus, viii. 11. 1, and Quintilian, i. 10. Val. Maximus does not say that Gallus predicted the eclipse, but explained the cause of it when it had occurred; and the same statement is made by Cicero, De Repub. i. 15. For an account of Sulpicius, see Hardouin's Index auctorum, Lemaire, i. 214.
2 An account of this event is given by Herodotus, Clio, § 74. There has been the same kind of discussion among the commentators, respecting the dates in the text, as was noticed above, note 4, p. 29: see the remarks of Brotier and of Marcus in Lemaire and Ajasson, in loco. Astronomers have calculated that the eclipse took place May 28th, 585 B.C.; Brewster, ut supra, pp. 414,419.
3 Hipparchus is generally regarded as the first astronomer who prosecuted the science in a regular and systematic manner. See Whewell, C. 3. p. 169 et seq., 177–179. He is supposed to have made his observations between the years 160 and 125 B.C. He made a catalogue of the fixed stars, which is preserved in Ptolemy's Magn. Const. The only work of his now extant is his commentary on Aratus; it is contained in Petau's Uranologie. We find, among the ancients, many traces of their acquaintance with the period of 600 years, or what is termed the great year, when the solar and lunar phenomena recur precisely at the same points. Cassini, Mem. Acad., and Bailly, Hist. Anc. Astron., have shown that there is an actual foundation for this opinion. See the remarks of Marcus in Ajasson, ii. 302, 303.
4 Seneca, the tragedian, refers to this superstitious opinion in some beautiful verses, which are given to the chorus at the termination of the fourth act of the Thyestes.
5 We have an account of this event in Thucydides, Smith's trans. ii. 244, and in Plutarch, Langhorne's trans. iii. 406. It is calculated to have happened Aug. 27th, 413 B.C.; Brewster, ut supra, p. 415, 421.
6 The elegant lines of Ovid, in his Fasti, i. 297 et seq., express the same sentiment: "Felices animos, quibus hoc cognoscere primis," &c.
7 I have already remarked upon the use of this term as applied to the eclipses of the moon in note4, p. 31.
Pliny (HN, XXXVI.XVII.82) and Plutarch (Conv. sept. sap. 147)
Quaes. Hom. 22, not the same as Heraclitus of Ephesus
Josephus (Contra Apionem I.2) wrote that Thales was a disciple of the Egyptians and the Chaldeans which suggests that he visited the Near-East. It is thought that Thales visited the Babylonians and Chaldeans and had access to the astrological records which enabled him to predict the solar eclipse of 585 B.C.E.
Plutarch (1952). "Solon". In Robert Maynard Hutchins. Lives. Great Books of the Western World 14. Chicago: William Benton. p. 66.
De Pythiae oraculis 18. 402 E
Ps.-Plutarch (Epit. III.10).Ps.-Plutarch, Epit;Pseudo-Plutarch, Epitome
De Is. et Os. 131
(Apul. Florida, 18).
(Philostratus, Life of Apollonius , II.V).
Cleomedes explained that the calculation could be made by running a water-clock, from which the result was obtained: the diameter of the sun is found to be one seven-hundred-and-fiftieth of its own orbit (Cleomedes, De Motu circulari corporum caelestium, II.75).
Lives of eminent philosophers (D.L. I.23)
Several other lists were compiled: Hippobotus (D.L. I.42); Pittacus (D.L. I.42); and Diogenes (D.L. I.13. They omitted some names and adding others. In his work On the Sages, Hermippus reckons seventeen, which included most of the names listed by other compilers.
Proclus acknowledged Thales as the discoverer of a number of specific theorems (A Commentary on the First Book of Euclid's Elements 65. 8-9; 250. 16-17).The development of geometry is preserved in a work of Proclus, A Commentary on the First Book of Euclid's Elements (64.12-65.13). Proclus provided a remarkable amount of intriguing information, the vital points of which are the following: Geometry originated in Egypt where it developed out of necessity; it was adopted by Thales who had visited Egypt, and was introduced into Greece by him
In isosceles triangles the angles at the base are equal; and if the equal straight lines are produced further, the angles under the base will be equal (Proclus, 244). It seems that Thales discovered only the first part of this theorem for Proclus reported: We are indebted to old Thales for the discovery of this and many other theorems. For he, it is said, was the first to notice and assert that in every isosceles the angles at the base are equal, though in somewhat archaic fashion he called the equal angles similar (Proclus, 250.18-251.2).
(Proclus, 352.12-15).(Proclus, 124). >(Proclus, 299.2-5)(Eudemus ap. Proclus, 65.7)
Fielding, Henry. 1775. An essay on conversation. John Bell. p. 346
Russell, Bertrand (1945). The History of Western Philosophy. New York: Simon and Schuster.
Wisdom of the West
Singer, C. (2008). A Short History of Science to the 19th century. Streeter Press. p. 35.
Doxographi Graeci Diels, Dox. p. 475)
A report from Theon of Smyrna ap. Dercyllides states that: 'Eudemus relates in the Astronomy that Thales was the first to discover the eclipse of the sun and that its period with respect to the solstices is not always constant'
(DK, 11 A 17).Hippolytus (Diels, Dox. 555)
Farrington, B., 1944 Greek Science. Pelican
Turner, Catholic Encyclopedia
(Boyer 1991, "Ionia and the Pythagoreans" p. 43)
Thoughts on Thales Jstor
J. L. Gesch (1925). D. Math. Und Naturwiss. im Altertum. Munich. p. 50.
Needham, C. W. (1978). Cerebral Logic: Solving the Problem of Mind and Brain. Loose Leaf. p. 75. ISBN 0-398-03754-X.
William G. Shute, William W. Shirk, George F. Porter, Plane and Solid Geometry, American Book Company (1960) pp. 25-27
Historian B.L. Van der Waerden is among those advocating the idea of Mesopotamian influence, writing "It follows that we have to abandon the traditional belief that the oldest Greek mathematicians discovered geometry entirely by themselves…a belief that was tenable only as long as nothing was known about Babylonian mathematics. This in no way diminishes the stature of Thales; on the contrary, his genius receives only now the honour that is due to it, the honour of having developed a logical structure for geometry, of having introduced proof into geometry."
D. R. Dicks (November 1959). "Thales". The Classical Quarterly 9 (2): 294–309. doi:10.1017/S0009838800041586.
Colin R. Fletcher (December 1982). The Mathematical Gazette (The Mathematical Association) 66 (438): 267.
Hesychius, recorded that '[Thales] wrote on celestial matters in epic verse, on the equinox, and much else' (DK, 11A2).
DK, Diels, Hermann and Walther Kranz.Die Fragmente der Vorsokratiker. Zurich: Weidmann, 1985.
Roger L. Cooke (2005). The History of Mathematics: A Brief Course. John Wiley & Sons, Inc.
taken from wikipedia. sources unknown. born in Miletus
taken from wikipedia. source unknown.