Tales de Mileto

Thales (fl. c.585 bc)

Known as the first Greek philosopher, Thales initiated a way of understanding the world that was based on reason and nature rather than tradition and mythology. He held that water is in some sense the basic material, that all things are full of gods and (purportedly) that all things possess soul. He predicted an eclipse of the sun and was considered the founder of Greek astronomy and mathematics.

1 Life and legacy

The first Presocratic philosopher and reputed founder of Western philosophy and science, Thales lived in the early sixth century bc in Miletus, a prosperous Ionian Greek city on the seaboard of Asia Minor. At Miletus he was followed in turn by Anaximander and Anaximenes, the other members of the so-called Milesian School. These two refined his rational approach to the study of nature and extended its application, leaving an intellectual legacy that was decisive for later Presocratic philosophers and, through them, for Plato, Aristotle and the Hellenistic philosophical schools, and consequently for the rest of the Western cultural tradition.

It is doubtful whether Thales wrote anything. Although ancient sources ascribe several works to him, no writing of his was available to Aristotle. Our knowledge depends entirely on the reports of others, many of which are inaccurate and even fanciful, thanks to the legendary status Thales achieved. Thales was the only Presocratic philosopher numbered among the Seven Sages, and this honour is probably due to his reputation for practical advice rather than for his scientific and philosophical work. He is said to have told the Ionian cities to form a political union with a common, centrally located governing council, the better to resist Persian aggression (Herodotus, I 170, A4) and to have advised the Lydian king Croesus how to ford the Halys River (I 75, A6). He was most famous for predicting a solar eclipse that took place on 28 May 585 bc (I 74, A5).

 

2 Philosophy

Thales is widely believed to have held that all things are made of water. This interpretation goes back at least to Aristotle (Metaphysics I 3, A12), who attributes it to Thales in summarizing the views of his predecessors which he regards as pertinent to his own investigation of aitiai (causes or explanatory factors). Thales, like ‘others who first pursued philosophy’, held that ‘the only principles (archai) of all things are principles in the form of matter’. He chose water as the unique material principle, in the sense that everything originally evolves from water and ultimately perishes into water and, more strongly, that all things are composed of water, which persists in them although its attributes change. Thus Thales is the first Ionian material monist and the founder of physical science (see Archē).

How accurately Aristotle’s interpretation represents Thales’ views is open to question, for it dresses Thales in Aristotelian language and concepts and presupposes that he was interested in the very problems that excited Aristotle two centuries later. Furthermore, it is possible that Aristotle’s account (‘Thales, the originator of this kind of philosophy, says it is water; this is why he declared that the earth rests on water’ (Metaphysics I 3, A12)) merely records Aristotle’s own inference that Thales held water to be the material principle on the basis of the view, which he confidently attributes to Thales, that the earth rests on water. This possibility, together with the weakness of the inference, makes it less likely that Thales was a material monist in Aristotle’s sense.

On an alternative theory, also based on ancient evidence, Thales borrowed the belief that the world floats on water from Egyptian and/or Babylonian creation myths such as the Enuma Elish (see Egyptian philosophy, influence on Ancient Greek thought §1). This view is not implausible since Thales reportedly visited Egypt and Miletus had commercial connections with Egypt and the Near East. According to these creation myths, the earth or land arose in the middle of primeval waters through the agency of one or more gods. Thales may thus have borrowed also the idea that water is the origin of the world, conceiving of it not as an Aristotelian material principle, but as the ultimate ancestor of all things. It may be significant that archē, Aristotle’s word for ‘principle’, also means ‘origin’ or ‘beginning’.

Even on this account Thales did more than borrow; he took a decisive step away from the traditional and mythological towards the philosophical and scientific by demythologizing the views he adopted. Not that he was an atheist; he and his successors believed strongly in the divine and its importance in the universe. However, they abandoned the traditional Greek tendency to explain events through the Olympian gods. Where tradition had attributed earthquakes to Poseidon, Thales explained them in terms of the motion of the water that supports the earth (Seneca, Natural Questions III 14, A15). This way of thinking is more apparent in the theories of later Presocratics than in what we know of Thales himself, but their agreement on this approach was doubtless one of Aristotle’s reasons for calling Thales the originator of materialism and for distinguishing him from purveyors of mythological accounts of creation.

Thales’ views on divinity and on soul are attested as follows. ‘He said that the magnet possesses soul (psychē) because it moves iron’ (Aristotle, On the Soul 405a20, A22) (see Psychē). ‘Some say that soul permeates the universe. This may have been Thales’ reason for thinking that all things are full of gods’ (On the Soul 411a7, A22). These reports have led some to describe Thales’ world view as panpsychism and pantheism, but such labels by themselves contribute little to understanding a philosopher’s thought. In the first place, the notion of soul needs clarification. Briefly and dogmatically, on the Greek view of soul which Aristotle develops and for which he finds evidence in Thales, the presence of soul is what makes something alive; non-living things have no soul, and dead things no longer have one. Signs of life include the capacities to move and change, and to cause other things to move and change. In Thales’ case we have three claims: (1) the magnet moves iron, therefore it possesses soul; (2) soul permeates the universe; and (3) all things are full of gods. Only (1) and (3) are explicitly attributed to Thales; (2) is conjectured to be his reason for holding (3), and no connection is asserted to hold between (1) and (3). Now (3) does not follow from (2) without further premises, including one that amounts to: (4) wherever there is soul, there are gods. If Thales held this view (a hypothesis that is historically plausible, if unprovable), then (1) becomes relevant, since it establishes that soul occurs in more things than people suppose, and hence provides support for (2). Even so, the argument falls short. Even granted that anything that makes other things move is alive, we need not suppose that everything whatsoever is alive. Still, this could be how Thales reasoned, in view of the Presocratic tendency to make generalizations on the basis of slender evidence.

This reconstruction of Thales’ reasoning is tentative and optimistic, for (1) and (3) are the only views ascribed to him, and he could have held them independently of one another. However, his views on the role of water in the universe support the connection of ideas suggested above. Briefly and dogmatically again, the Greeks commonly held that anything was divine that was immortal and had the power to affect things independently of human will. On the second account of water presented above, water could be considered as divine and (for reasons given above) also as possessing soul. Things made out of water, or ultimately descended from water – that is, all things – thus have a claim to possessing soul and being divine, although these properties are more or less obvious in different things (just as some things are wetter than others).

3 Mathematics and astronomy

As Aristotle made Thales the originator of philosophy, so Aristotle’s student Eudemus, who wrote histories of geometry and astronomy, made him the first Greek mathematician and astronomer. Here too the nature of his originality and contributions is uncertain. Reportedly he brought geometry to Greece from Egypt, where it was used for practical purposes and ‘attacked some [theorems] more generally and others more perceptually’ (Proclus, On the First Book of Euclid’s Elements 65.3, A11). He was the first to prove that a circle is bisected by its diameter (157.10, A20), and to know that triangles having one side and the two adjacent angles equal are congruent, ‘since he must have used this theorem in his method for demonstrating the distance of ships at sea’ (352.14, A20). He is also credited with discovering several other theorems. The evidence supports different interpretations, from the extreme position that Thales stated and proved certain theorems exactly as they appear in Euclid, to the other extreme that he was no mathematician at all, but that Eudemus attributed certain results to him in order to give geometry as noble an ancestry as philosophy. An intermediate view is preferable; that he made certain discoveries about spatial relations and used them to solve practical problems, but did not have a general conception of mathematical proof, let alone of a Euclidean axiomatization of geometry, and probably did not even state the propositions generally. He is explicitly credited with proving only the claim about the circle – a proposition which Euclid does not prove, but incorporates into his definition of the diameter of a circle (Elements I def. 17). He may have proved this result by ‘superposition’ – drawing a circle, cutting it along a diameter, and seeing that one piece fits exactly over the other. This is not a rigorous demonstration, but since it shows that one fact follows from another and holds generally of all circles, not only the one used in the proof, it contains the essence of the conception of mathematical proof, and would represent a decisive advance from the problem-solving and rule-oriented approach of the Egyptians and Babylonians.

In astronomy he was credited with many discoveries, but in the end his fame as an astronomer rests on his prediction of the eclipse. However, even this cannot be accepted straightforwardly. For Thales certainly lacked the knowledge needed to predict eclipses by modern methods. At most he reported a Babylonian prediction: the Babylonians had methods of predicting when eclipses might occur, and there is nothing improbable about Thales’ having come into contact with such knowledge.

The central problem in assessing Thales’ contribution concerns his originality and his borrowing from others: how much was there of each, and what relative value are we to assign them? The evidence is unanimous in singling him out as a great innovator, and it would be rash to deny him all claims to importance, even if much of what he professed was due to others, especially non-Greeks. Later Ionian philosophers admired him and recognized him as their predecessor, and their ideas and methods are plausibly interpreted in terms of a historical sequence that originated with his evident curiosity about the world, his polymathy and his rational approach.