Information on Thales' life and philosophical views is incomplete. What exists are short statements in the works of others on his views on various topics, including physics, mathematics and astronomy, and a few stories about about him. Further hindering the historical task is the fact that it is not certain how reliable the sources are that relate Thales' views and biographical details about him. Plato says that Thales was numbered as one of the seven wise men of Greek culture (Protagoras 343a) (see Hipp. 1; Dox. 555). Possessing such an elevated status in the Greek world might tend to historical fabrication, as is sometimes the case with people who are the focus of intense interest and admiration. There is no indication that Thales wrote anything; his views seemed to have been passed down orally.
According to Herodotus, Thales was of Phoenician descent (Herod. 1.170), and once foretold a solar eclipse (on May 28, 585 BCE) that brought to an end a war between the Lydians and Medes (Herod. 1.74). There are two apophthegmata (stories that make a point) about Thales passed on by Plato and Aristotle; whether either is true and to which extent is impossible to determine. Nevertheless, they may give an accurate portrayal of Thales.
Plato has Socrates relate the story of how Thales was once walking and at the same time studying the stars when he fell into a well. A Thracian slave girl mocked him for being so concerned with what was in the sky that he did not see what was at his feet (Theaetetus 174a). In order to make the point that philosophy is not only impractical, but even dangerous to one's well-being, Thales is made to appear ridiculous in this apophthegma.
Conversely, Aristotle relates an apophthegma about Thales, which puts
him in a favorable light. Thales was derided for his poverty, which
was the result of his obsession with philosophy. In an effort to
prove that his poverty was voluntary, he determined the precise time
of the olive harvest by studying the stars; he then went out and rented
all the olive presses for that time, and rented them out again at a
huge profit (Politics 1259a 9). The moral of the story is that
philosophy can be very profitable, if philosophers choose to turn it
to that end.
Knowledge of Thales' philosophical views derives principally from references to them by others; Aristotle is the first to do so, but he does not disclose his sources for Thales' views. It must also be pointed out that Aristotle uses his own philosophical terminology when summarizing Thales' own views, and so may inadvertently be guilty of distortion resulting from anachronism. It is possible that those who subsequently discuss Thales' views may dependent on Aristotle's works.
Aristotle explains Thales' philosophical views as follows:
Of the first philosophers, then, most thought the principles (tas archas) which were of the nature of matter (tas en hulês) were the only principles of all things (archas pantôn)....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.
Some think that even the ancients who lived long before the present generation, and first framed accounts of the gods, had a similar view of nature; for they made Ocean and Tethys the parents of creation, and described the oath of the gods as being by water, to which they give the name of Styx; for what is oldest is most honorable, and the most honorable thing is that by which one swears. It may perhaps be uncertain whether this opinion about nature is primitive and ancient, but Thales at any rate is said to have declared himself thus about the first cause. Hippo no one would think fit to include among these thinkers, because of the paltriness of his thought. (Metaphysics 983b 7-27)
For Aristotle, a principle (archê) is that which explains and causes the existence of another. According to him, Thales proposes that water, one of the four elements, is the principle (archê) of all things, which means that the first principle is material or made of matter (hulê). In other words, water is the origin of all things, that from all things emerge and to which they return; moreover, all things ultimately are water. The diversity of the world of common sense is the result of the modification of water to appear as something other than water. Water is that which is unchanging in a world of becoming. In one sense, Thales's view is that there is no true coming to be or passing away because all things are ultimately water, so that change is mere appearance, and is not ultimately real. In this way, according to Thales, reality is different from appearance because not everything appears to be one unchanging thing. Aristotle also relates that Thales believes that the earth rests on water (983b 21; see also On the Heavens 294a 28). It seems that if it must rest upon anything at all, the earth, which is water, must rest upon the first material principle, water.
Other statements of Thales' view that water is the first material principle occur in later writers. Of interest is the statement by Hippolytus in his Refutation of All Heresies:
It is said that Thales of Miletus, one of the seven wise men, was the first to undertake the study of physical philosophy. He said that the archê (principle) and the end of all things is water. All things acquire firmness as this solidifies, and again as it is melted their existence is threatened; to this are due earthquakes and whirlwinds and movements of the stars. And all things are movable and in a fluid state, the character of the compound being determined by the nature of the principle from which it springs (Hippolytus, Refut. 1; Dox. 555).
From Hippolytus' statement, it seems that Thales explains the emergence of all things as the solidification of water to become the basic elements from which all things are then compounded; when things revert to liquid form, however, they pass out of being. Somehow this process of solidification and liquidification causes earthquakes, whirlwinds and the movement of the stars. To say that water is the end of all things seems to mean that ultimately everything will become what it already is, water.
Based on the available sources, the reasoning process behind Thales's conclusion that water is the first material principle is unknown and so a matter of conjecture. In the above quotation, Aristotle hypothesizes that the reason that Thales postulates that water is the first material principle is because water and heat are the basis of all life and water is the basis of heat. (He seems to conceive as heat as produced by water somehow.) He says that Thales arrives at his view "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." If Aristotle is correct, Thales extrapolates from his experience of the centrality of water (and heat) to life to the conclusion that all things—living and not living—are water. Aristotle also suggests that Thales to some extent has come under the influence of the mythological portrayal of the origins of all things, in which water is central: "For they [the ancients] made Ocean and Tethys the parents of creation, and described the oath of the gods as being by water, to which they give the name of Styx; for what is oldest is most honorable, and the most honorable thing is that by which one swears." (Ocean is the son of Ouranos [Heaven] and Gaia [Earth] and Tethys is a Titaness and sea-goddess, being both the sister and wife of Ocean. Styx is the primordial river forming the boundary between earth and the underworld.) It must be stressed, however, that Aristotle is conscious that he is presenting only a hypothesis about the origin of Thales' views.
There is another possible reason that Thales concludes that water is the first material principle. Since it is only water that in ordinary experience human beings see being transformed in its three phases (solid, liquid and gas), perhaps Thales reasons that all things must be water. In other words, if nothing else is known to change phases of matter, then that which does, i.e., water, must the source of all other things.
Aristotle makes the odd remark about Thales that he thinks, "All things are full of gods" (On the Soul 405a 19). Similarly, Hippolytus says that for Thales: "This principle [water] is God, and it has neither beginning nor end" (Refut. 1). How can it be that all things are full of gods and that water is God? Aetius may provide some information about Thales' view that may allow for an explanation: "Thales said that the mind in the universe is God, and the all is endowed with soul and is full of spirits; and its divine moving power pervades the elementary water (Aet. 1. 7; Dox. 301). Thales's view seems to be as follows. As most Greeks, he holds that soul is the cause of all motion, even of inanimate objects. Thus, since there is motion, there must be a soul causing each instance of motion. (This would explain why Thales in reputed to have said that the magnet has a soul, for otherwise it would not be able to cause motion [On the Soul A. 2; 405a 19].) He then takes a further step and concludes that soul, or the cause of motion, is a god or God. This is probably the meaning of his statement that all things are full of gods (Aristotle) or spirits (Aetius). For every instance of motion at a given time there must be a soul or a god causing it. The reason that he identifies water with God is because he holds, as most Greeks do, that whatever is eternal is divine. Thus, since it as the first material principle is eternal, water must be God. This would make sense of Clement of Alexandria's statement: "For Thales being asked, What is the divinity? said, 'What has neither beginning nor end'" (Strom. 5.14). Perhaps Thales believes that, as divine, water is permeated by mind or God, which is the moving force behind the permutations of water into all things; in other words, water is the soul of all things. But how does Thales move from belief in one God to many gods on the basis of his belief that water is God? It is possible he holds that the one God or mind fragments itself to become the moving forces behind all individual moving things; thus the "gods" as the cause of motion are really only manifestations of one God. Clearly, Thales's first material principle—water—is more than just ordinary water; rather it is the eternal source of all things..