The third of the Dhilosophers of the school of Miletus is Anaximenes. We have no precise dates for his life and know only that he was a younger "associate" of Anaximander. Like Anaximander he wrote a book and seems to have employed a style that was less poetical than that of the elder philosopher. The important references to him from later sources are quoted by Burnet and are as follows:
1. Anaximenes of Miletus, son of Eurystratus, who had been an associate of Anaximander, said, like him, that the under-lying substance was one and infinite. He did not, however, say it was indeterminate, like Anaximander, but determinate; for he said it was Air.
2. From it, he said, the things that are, and have been, and shall be, the gods and things divine, took their rise, while other things came from its offspring.
3. "Just as," he said, "our soul, being air, holds us together, so do breath and air encompass the whole world."
4. And the form of the air is as follows. Where it is most even, it is invisible to our sight; but cold and heat, moisture and motion, make it visible. It is always in motion; for, if it were not, it would not change so much as it does.
5. It differs in different substances in virtue of its rarefaction and condensation.
6. When it is dilated so as to be rarer, it becomes fire; while winds, on the other hand, are condensed Air. Cloud is formed from Air by felting; and this, still further condensed, becomes water. Water, condensed still more, turns to earth; and when condensed as much as it can be, to stones.
In comparing Anaximenes with Anaximander perhaps our modern distinction between the philosopher and the scientist may be of use. It appears that Anaximenes was more of a scientist and less of a philosopher than his predecessor. He was interested in how things worked rather than in what they were. Thus he was not trying to answer quite the same question as that which had occurred to the mind of Anaximander. When Anaximander thought of the primary substance or substratum, he was asking himself "What is it that every particular thing is a form of? " This question, it would seem, can only be answered (if it can be answered at all) by saying "Some stuff which is not itself of any particular kind." This stuff, indeed, must be "unlimited" in the sense of being "indeterminate," and, as an answer to the question, "air" is no improvement on "water."
But the question which Anaximenes asked himself seems to have been of a more "practical" or "scientific" kind. He was interested not in what is more fundamental than any kind of thing, but simply in what particular kind of thing is most fundamental. It is, of course, very likely that he was himself quite unaware that these are different questions.
So far as his own particular question is concerned, air seems to be as good a speculative answer as any. The theory of rarefaction and condensation as being the factors which account for difference cannot be original. (Thales must have held the same view about water.) Much more significant is the view, which we have expressed in Anaximenes' own words, that "just as our soul, being air, holds us together, so do breath and air encompass the whole world." Here life is directly connected with the primary substance. Later theories of a more mystical nature — theories, for instance, of a "world-soul" — could look back for support to this doctrine of Anaximenes.
Curiously, Anaximenes with his "scientific" approach and his comparatively clear style was less fruitful as a scientist than was the more philosophical and "poetical" Anaximander. Anaximander had held that the cylindrical earth remains suspended in space because there is no reason why it should move in any one particular direction rather than in another. Anaximenes reverted to the flat-earth theory. For him the earth and the heavenly bodies are flying saucers, or rather saucers floating on air. Neither of the two theories would be regarded today as correct; but the theory of Anaximander held more promise.