ΠΕΡΙ ΖΩΙΩΝ ΚΙΝΗΣΕΩΣ
I. Περὶ δὲ κινήσεως τῆς τῶν ζῴων, ὅσα μὲν αὐτῶν περὶ ἕκαστον ὑπάρχει γένος, καὶ τίνες διαφοραί, καὶ τίνες αἰτίαι τῶν καθ᾿ ἕκαστον συμβεβηκότων αὐτοῖς, ἐπέσκεπται περὶ ἁπάντων ἐν ἑτέροις· ὅλως δὲ περὶ τῆς κοινῆς αἰτίας τοῦ κινεῖσθαι 5κίνησιν ὁποιανοῦν (τὰ μὲν γὰρ πτήσει κινεῖται τὰ δὲ νεύσει τὰ δὲ πορείᾳ τῶν ζῴων, τὰ δὲ κατ᾿ ἄλλους τρόπους τοιούτους) ἐπισκεπτέον νῦν.
Ὅτι μὲν οὖν ἀρχὴ τῶν ἄλλων κινήσεων τὸ αὐτὸ ἑαυτὸ κινοῦν, τούτου1 δὲ τὸ ἀκίνητον, καὶ ὅτι τὸ πρῶτον κινοῦν ἀναγκαῖον ἀκίνητον 10εἶναι, διώρισται πρότερον, ὅτεπερ καὶ περὶ κινήσεως ἀϊδίου, πότερον ἔστιν ἢ οὐκ ἔστι, καὶ εἰ ἔστι, τίς ἐστιν. δεῖ δὲ τοῦτο μὴ μόνον τῷ λόγῳ καθόλου λαβεῖν, ἀλλὰ καὶ ἐπὶ τῶν καθ᾿ ἕκαστα καὶ τῶν αἰσθητῶν, δι᾿ ἅπερ καὶ τοὺς καθόλου ζητοῦμεν λόγους, καὶ ἐφ᾿ ὧν ἐφαρμόττειν οἰόμεθα 15δεῖν αὐτούς. φανερὸν γὰρ καὶ ἐπὶ τούτων ὅτι ἀδύνατον κινεῖσθαι μηδενὸς ἠρεμοῦντος, πρῶτον μὲν ἐν αὐτοῖς τοῖς ζῴοις. δεῖ γάρ, ἂν κινῆταί τι τῶν μορίων, ἠρεμεῖν τι· καὶ διὰ τοῦτο αἱ καμπαὶ
On the Movement of Animals
I. We have inquired elsewherea into the details of the movement of the various kinds of animals, the differences between these movements, and the causes of the characteristics which each exhibit; we must now inquire generally into the common cause of animal movement of whatever kind—for some animals move by flight, some by swimming, some by walking, and others by other such methods.
Now that the origin of all the other movements is that which moves itself, and that the origin of this is the immovable, and that the prime mover must necessarily be immovable, has already been determined when we were investigatingb whether or not eternal movement exists, and if it does exist what it is. And this we must apprehend not merely in theory as a general principle but also in its individual manifestations and in the objects of sense-perception, on the basis of which we search for general theories and with which we hold that these theories ought to agree. For it is clear also in the objects of sense-perception that movement is impossible if there is nothing in a state of rest, and above all in the animals themselves. For if any one of their parts moves, another part must necessarily be at rest; and