Early Greek Philosophy by John Burnet, with Burnet's notes
25. Theory of the Primary Substances 27. Air

From Chapter I., The Milesian School

26. Rarefaction and Condensation
At first, this looks like a falling off from the more refined doctrine of Anaximander to a cruder view; but this is not really the case. On the contrary, the introduction of rarefaction and condensation into the theory is a notable advance.112 In fact, it makes the Milesian cosmology consistent for the first time; since a theory which explains everything as a form of a single substance is clearly bound to regard all differences as quantitative. The only way to save the unity of the primary substance is to say that all diversities are due to the presence of more or less of it in a given space. And when once this step has been taken, it is no longer necessary to make the primary substance something "distinct from the elements," to use Aristotle's inaccurate but convenient phrase; it may just as well be one of them.

Burnet's Notes


112. Simplicius, Phys. p. 149, 32 (R. P. 26 b), says that Theophrastos spoke of rarefaction and condensation in the case of Anaximenes alone. It should be noted, however, that Aristotle, Phys. A, 4. 187 a 12, seems to imply that Anaximander too had spoken of rarefaction and condensation, especially if ὅ ἐστι πυρὸς μὲν πυκνότερον ἀέρος δὲ λεπτότερον is referred to him. On the other hand, at 20, οἱ δ' ἐκ τοῦ ἑνὸς ἐνούσας τὰς ἐναντιότητας ἐκκρίνεσθαι, ὥσπερ Ἀναξίμανδρός φησι seems to be opposed to a 12, οἱ μὲν κτλ. As I have indicated already, it looks as if we were dealing here with Aristotle's own inferences and interpretations, which are far from clear. They are outweighed by the definite statement quoted by Simplicius from Theophrastos, though Simplicius himself adds δῆλον δὲ ὡς καὶ οἱ ἄλλοι τῇ μανότητι καὶ πυκνότητι ἐχρῶντο. That, however, is only his own inference from Aristotle's somewhat confused statement.

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