From the Beginning to Plato

58 FROM THE BEGINNING TO PLATO
both issues, and may be supposed to be what prompted the junior thinker to
engage with them. In any event the result is a cosmology resembling
Anaximander’s in many respects, but at these key points advancing substantive
theses. It is succinctly summed up by Simplicius in a passage deriving from
Theophrastus:
Anaximenes son of Eurystratus, of Miletus, a companion of Anaximander,
also says, like him, that the underlying nature is one and infinite, yet not
indefinite as Anaximander said, but determinate—for he identifies it as air.
It differs in thinness and thickness according to the substances which it
constitutes, and if thinned becomes fire, if thickened wind, then cloud, then
(thickened further) water, then earth, then stones. Other things come from
these. He, too, makes motion eternal, and says that change, as well, comes
about because of it.
(Simplicius Physics 24.26ff. [KRS 140])
The hypothesis that the first principle is air in eternal motion enables
Anaximenes to fill both the principal lacunae in Anaximander’s theory. It
ventures a definite characterization of the apeiron; and in so doing it facilitates
an explanation of the emergence of the chief phenomena studied by natural
philosophy: the opposite processes of thinning and thickening to which air is
subject are what produce fire, on the one hand, and a series—to become
canonical in subsequent Ionian thought —of more and more condensed forms of
matter, on the other.
It has often been thought that a text of Aetius reports an analogical argument
presented by Anaximenes for the claim that air is the first principle. The passage
in question begins with the information that this was his principle, and then, on
the traditional interpretation, continues with the words:
As (hoion) our soul, he says, being air controls us, so (kai) pneuma and air
enclose the whole world. (Air and pneuma are synonymous here.)
(Aetius I.3.4 [KRS 160])
This statement has usually been given prominence in reconstructions of
Anaximenes’ philosophy. It has even been taken as an actual fragment of his
book. Its precise logic and overall point have been much discussed, but
(assuming always that the translation given above is correct) the context would
favour an interpretation which finds some kind of inference from microcosm to
macrocosm: as air is the principle of human life, so it is the principle of the cosmos
at large.
On further examination Aetius’ sentence proves unable to bear such a weight
of interpretation. To begin with, it cannot be an actual quotation from
Anaximenes. His book was written ‘in simple and economical Ionic’. Aetius’
sentence is not in Ionic. It also includes at least one word coined much later than