Anaximenes ... also says that the underlying nature is one and infinite ... but not undefined as Anaximander said but definite, for he identifies it as air; and it differs in its substantial nature by rarity and density. Being made finer it becomes fire; being made thicker it becomes wind, then cloud, then (when thickened still more) water, then earth, then stones; and the rest come into being from these.

Anaximenes and Anaxagoras and Democritus say that its [the earth's] flatness is responsible for it staying still: for it does not cut the air beneath but covers it like a lid, which flat bodies evidently do: for they are hard to move even for the winds, on account of their resistance.

Anaximenes son of Eurystratus, of Miletus, was a pupil of Anaximander; some say he was also a pupil of Parmenides. He said that the material principle was air and the infinite; and that the stars move, not under the earth, but round it. He used simple and economical Ionic speech. He was active, according to what Apollodorus says, around the time of the capture of Sardis, and died in the 63rd Olympiad.

Anaximenes ... declared that air is the principle of existing things; for from it all things come-to-be and into it they are again dissolved. As our soul, he says, being air holds us together and controls us, so does wind [or breath] and air enclose the whole world.