Aristotle, On the Heavens

LCL 338: 256-257

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Aristotle

Γ

Of the Four Sublunary Bodies

Chapter I

Argument

To treat of the sublunary elements involves a theory of generation. Previous views on generation: (1) It is all illusion, since what is is unchangeable and imperishable. (2) Everything which we see is in a flux of generation, change, and decay, but there is one persistent underlying substance out of which the world and its phenomena are evolved. (3) All natural bodies are generated, their ultimate elements being plane surfaces (298 a 24—299 a 1).

The last theory (that of Plato) is criticized in detail, expressly from the point of view of the natural scientist and not of the mathematician (299 a 1—300 a 19).

(a) Natural bodies have weight, therefore their parts, however small, must have weight, therefore surfaces must have weight, and if surfaces then lines and points (since on the view criticized the elements of body are surfaces, of surfaces lines, and of lines points). But a point cannot have weight, because it is by definition indivisible, and everything which has weight can be shown to be divisible (299 a 25—b 23).

289 a Περὶ μὲν οὖν τοῦ πρώτου οὐρανοῦ καὶ τῶν 24, 25μερῶν, ἔτι δὲ περὶ τῶν ἐν αὐτῷ φαινομένων1 ἄστρων,

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On the Heavens, III. i.

Book III

Of the Four Sublunary Bodies

Chapter I

Argument (continued)

(b) The Timaeus would have us believe that surfaces only combine edge to edge, since they have to form the pyramids, cubes, etc., which on Plato’s theory are the constituents of the four primary bodies. But we cannot believe this. It would be just as easy for them to lie one upon another, but if they do, what sort of body would result? (299 b 23–31.)

(c) It is said in the Timaeus that the primary bodies differ in weight according to the number of equal triangular surfaces comprising each of their “seeds” But if so we are back at the difficulty of supposing that surfaces (and hence points) have weight. Even if we simply affirm earth to be heavy and fire light, this must result from a property of the surfaces which compose their “seeds” (299 b 31—300 a 7).

The result of the theory then is to dissolve all body and magnitude into thin air. Applied to time, it has the same effect. And the criticisms to which it is open apply with equal force to the Pythagorean theory which generates the world from numbers: weightless monads can never be the sole ultimate components of bodies possessed of weight (300 a 7–19).

We have treated earlier of the first heaven and its parts, and also of the stars which are visible

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DOI: 10.4159/DLCL.aristotle-heavens.1939