Simplicius on De caelo #1: On Book 1, chapter 1

Excerpted from R.J. Hankinson, Simplicius: On Aristotle's 'On the Heavens 1.1-4'.

From the Prologue.

"Alexander says that the subject of Aristotle's treatise On the Heavens is the world. He says that 'heaven' [ouranos] is used in three senses by Aristotle in this work, to mean both the sphere of the fixed stars and the whole of the divine revolving body, which in this book he also calls the 'furthest heaven' (with the adjective), and additionally 'the world', as Plato called it when he said 'the whole heaven, or the world or whatever else it might care to be called'. And he adduces Theophrastus as witness, since he talks in his On the Heavens not only of the divine body but also about things which come to be and about their principles. Thus Alexander says [the treatise] is about the world and the five bodies in it, that of the heaven and the four of the sublunary world, fire, air, water, earth.

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The divine Iamblichus, on the other hand, says that, having set up the heavenly and divine body as the subject of this work, Aristotle in fact includes the study of the whole world, since it is substantially contained in it and under its control in regard to the production of generation; although it is also concerned with the elements and the powers that inhere in them, since all of these things depend upon the heaven and the things which revolve with it.

The great Syrianus and his followers say that the treatise concenrs the heaven proper, i.e. the eternal, revolving body, relying, it seems, on the title, and not accepting Alexander's claim.

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[V]ery little is said about the world as a whole [in this work], and only such things as it has in common with the heaven, i.e. that it is eternal, limited in size, and single, and that it has these features because the heaven is eternal, limited and single. But if anyone wishes to inspect Aristotle's theory of the world, it must be said that he presents his account of the world in all of his physiccal treatises taken together.

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[I]t seems to me clearly to be the case that in these books Aristotle treats of both the heavens and the sublunary four elements. [...] Of these the first is the heavenly body, which gives its title to the treatise as being more worthy of honour[.]"