chance can exist in eternal things, but the heaven is eternal and its circular motion, for what reason then does it move in one direction, and not in the other? For it is necessary that this too is a principle or has a principle. For if nature always does what is best of the possibilities, and just as with rectilinear motions the motion towards the upper place is more honorable (for the upper place is more divine than the lower), in the same way the motion forwards is related to the motion backwards, just as is the right and the left. The difficulty that was raised bears witness that there is a prior and a posterior; for this is the cause that resolves the difficulty. For if it is in the best possible state, this would be the cause of what has been said; for it is best to be moved with a simple and ceaseless motion, and this towards what is more honorable. If nature, which always does the best of the possibilities, made the heaven move forward and not backward, how is the heaven and its motion eternal, having been generated by nature and having the best possible motion? If the forward motion has the same difference with respect to the backward motion as the upper place has to the lower, in respect of being more honorable and more divine and better, how are these motions, which differ so much from each other, not contrary? If the motion of simple bodies is simple, not according to possibility but according to necessity, how can the heaven, which has a simple body, be able to be moved in two ways, and be moved contingently? If the heaven is everywhere equal to itself, and having its parts equal to its parts, and in whatever way it moves it preserves its spherical and circular motion, it is able then to be moved also from south to north and from north to south, just as it is able to be moved from east to west and from west to east. How then has nature not placed in vain in the body of the heaven the capacities for so many motions, if it has the capacities in four ways, but is moved in only one? ne. From the same argument. Concerning the so-called stars, it would be next to speak, of what they are composed and what their motions are. But it is most reasonable and follows from what has been said to make each of the stars out of that body in which it happens to have its motion, since we said there is something that is by nature carried in a circle; for just as those who affirm them to be of fire say this because they say the upper body is fire, as it is reasonable that each thing is composed of those things in which each thing is, so too do we say. And the heat and the light from them are generated by the friction of the air under their motion. For motion is by nature able to set on fire even stones and wood and iron; it is more reasonable therefore for that which is nearer to fire, and the air is nearer as also in the case of flying arrows; for these are set on fire so that their leaden parts melt, and since they themselves are set on fire, it is necessary that the air around them also

ταὐτομάτου ἐνδέχεται ἐν τοῖς ἀϊδίοις εἶναι, ὁ δὲ οὐρανὸς ἀΐδιος καὶ ἡ κύκλῳ φορά, διὰ τίνα ποτὲ αἰτίαν ἐπὶ θάτερα φέρεται, ἀλλ' οὐκ ἐπὶ θάτερα; Ἀνάγκη γὰρ καὶ τοῦτο ἀρ χὴν εἶναι ἢ εἶναι αὐτοῦ ἀρχήν. Eἰ γὰρ ἡ φύσις ἀεὶ ποιεῖ τῶν ἐνδεχομένων τὸ βέλτιστον, ἔστι δὲ καθάπερ τῶν ἐπὶ τῆς εὐθείας φορῶν ἡ πρὸς τὸν ἄνω τόπον τιμιωτέρα (θειότερος γὰρ ὁ τόπος ὁ ἄνω τοῦ κάτω), τὸν αὐτὸν τρόπον καὶ ἡ εἰς τὸ πρόσθεν τῆς εἰς τὸ ὄπισθεν ἔχει, εἴπερ καὶ τὸ δεξιὸν καὶ τὸ ἀριστερόν. Μαρτυρεῖ δ' ἡ ·ηθεῖσα ἀπορία, ὅτι τὸ πρότερον καὶ τὸ ὕστερον· αὕτη γὰρ ἡ αἰτία λύει τὴν ἀπο ρίαν. Eἰ γὰρ ἔχει ὡς ἐνδέχεται βέλτιστα, αὕτη ἂν εἴη αἰ τία καὶ τοῦ εἰρημένου· βέλτιστον γὰρ κινεῖσθαι ἁπλῆν τε κίνησιν καὶ ἄπαυστον, καὶ ταύτην ἐπὶ τὸ τιμιώτερον. Eἰ τὸν οὐρανὸν ἡ φύσις ἐποίησε κινηθῆναι εἰς τὸ ἔμ προσθεν καὶ μὴ εἰς τὸ ὀπίσω, ἡ ἀεὶ τῶν ἐνδεχομένων τὸ βέλτιστον ποιουμένη, πῶς ἀΐδιος ὁ οὐρανὸς καὶ ἡ τούτου φορά, ὑπὸ τῆς φύσεως γεγενημένος καὶ τὸ τὴν βελτίστην κι νηθῆναι κίνησιν ἔχων; Eἰ τὴν διαφοράν, ἣν ἔχει ὁ ἄνω τόπος πρὸς τὸν κάτω, ταύτην ἔχει ἡ εἰς τὸ πρόσθεν κίνησις πρὸς τὴν εἰς τὸ ὄπισθεν κίνησιν κατὰ τὸ τιμιώτερον καὶ θειότερον καὶ βέλτιστον, πῶς οὐκ εἰσὶν ἐναντίαι αἱ κινήσεις αὗται το σοῦτον ἀλλήλων διαφέρουσαι; Eἰ τῶν ἁπλῶν σωμάτων ἡ κίνησις ἁπλῆ, οὐ κατὰ τὸ ἐνδεχόμενον ἀλλὰ κατὰ τὸ ἀναγ καῖον, πῶς διχῶς κινηθῆναι δύναται ὁ οὐρανὸς ἁπλοῦν σῶμα ἔχων καὶ κινεῖται ἐνδεχομένως; Eἰ πανταχόθεν ἐστὶν ὁ οὐρανὸς ἴσος ἑαυτῷ, καὶ ἴσα ἔχων τὰ μέρη τοῖς μέρεσι, καὶ ὡς ἐὰν κινηθῇ τὴν σφαιρικήν τε καὶ ἔγκυκλον σώζει κί νησιν, δύναται ἄρα καὶ ἀπὸ μεσημβρίας κινηθῆναι εἰς ἄρκτον καὶ ἀπὸ ἄρκτου εἰς μεσημβρίαν, ὡς δύναται κινηθῆναι ἀπὸ ἀνατολῆς εἰς δύσιν καὶ ἀπὸ τῆς δύσεως εἰς ἀνατολήν. Πῶς οὖν οὐ μάτην ἡ φύσις τῷ σώματι τοῦ οὐρανοῦ ἐνέθηκε το σούτων κινήσεων τὰς δυνάμεις, εἰ τετραχῶς μὲν ἔχει τὰς δυνάμεις, μοναχῶς δὲ κινεῖται; νε. Ἐκ τοῦ αὐτοῦ λόγου. Περὶ δὲ τῶν καλουμένων ἄστρων ἑπόμενον ἂν εἴη λέ γειν, ἐκ τίνων συνεστᾶσι καὶ τίνες αἱ κινήσεις αὐτῶν. Eὐλο γώτατον δὲ καὶ τοῖς εἰρημένοις ἑπόμενον τὸ ἕκαστον τῶν ἄστρων ποιεῖν ἐκ τούτου τοῦ σώματος ἐν ᾧ τυγχάνει τὴν φορὰν ἔχον, ἐπειδὴ ἔφαμέν τι εἶναι ὃ κύκλῳ φέρεσθαι πέ φυκεν· ὥσπερ γὰρ οἱ πύρινα φάσκοντες εἶναι διὰ τοῦτο λέ γουσιν, ὅτι τὸ ἄνω σῶμα πῦρ εἶναί φασιν, ὡς εὔλογον ὂν ἕκαστον συνεστάναι ἐκ τούτων ἐν οἷς ἕκαστον ἐστίν, ὁμοίως καὶ ἡμεῖς λέγομεν. Ἡ δὲ θερμότης ἀπ' αὐτῶν καὶ τὸ φῶς γίνεται παρατριβομένου τοῦ ἀέρος ὑπὸ τῆς ἐκείνων φορᾶς. Πέφυκε γὰρ ἡ κίνησις ἐκπυροῦν καὶ λίθους καὶ ξύλα καὶ σίδηρον· εὐλογώτερον οὖν τὸ ἐγγύτερον τοῦ πυρός, ἐγγύτερον δὲ ὁ ἀὴρ οἷον καὶ ἐπὶ τῶν φερομένων βελῶν· ταῦτα γὰρ ἐκπυροῦται οὕτως ὥστε τήκεσθαι τὰς μολυβδίδας, καὶ ἐπεί περ αὐτὰ ἐκπυροῦται, ἀνάγκη καὶ τὸν κύκλῳ αὐτῶν ἀέρα τὸ