§1Περὶ δὲ κινήσεως τῆς τῶν ζῴων, ὅσα μὲν αὐτῶν περὶ 1 ἕκαστον ὑπάρχει γένος, καὶ τίνες διαφοραί, καὶ τίνες αἰτίαι τῶν καθʼ ἕκαστον συμβεβηκότων αὐτοῖς, ἐπέσκεπται περὶ ἁπάντων ἐν ἑτέροις· ὅλως δὲ περὶ τῆς κοινῆς αἰτίας τοῦ κινεῖσθαι κίνησιν ὁποιανοῦν (τὰ μὲν γὰρ πτήσει κινεῖται τὰ δὲ νεύσει τὰ δὲ πορείᾳ τῶν ζῴων, τὰ δὲ κατʼ ἄλλους τρόπους τοιούτους) ἐπισκεπτέον νῦν.
Regarding the movement of animals, the characteristics that belong to each genus of them, what their differences are, and what the causes of the attributes belonging to each are, have been investigated concerning all of them in other works; but we must now investigate generally the common cause of undergoing any movement whatever (for some animals move by flight, others by swimming, others by walking, and others in other such ways).
ὅτι μὲν οὖν ἀρχὴ τῶν ἄλλων κινήσεων τὸ αὐτὸ ἑαυτὸ κινοῦν, τούτου δὲ τὸ ἀκίνητον, καὶ ὅτι τὸ πρῶτον κινοῦν ἀναγκαῖον ἀκίνητον εἶναι, διώρισται πρότερον, ὅτεπερ καὶ περὶ κινήσεως ἀϊδίου, πότερον ἔστιν ἢ οὐκ ἔστι, καὶ εἰ ἔστι, τίς ἐστιν.
Now, that the principle of other movements is that which moves itself, and the principle of this is the unmoved, and that the first mover must of necessity be unmoved, has been determined before, at the time when we also discussed eternal movement, whether it exists or does not exist, and if it exists, what it is.
δεῖ δὲ τοῦτο μὴ μόνον τῷ λόγῳ λαβεῖν, ἀλλὰ καὶ ἐπὶ τῶν καθʼ ἕκαστα καὶ τῶν αἰσθητῶν, δι᾿ ἅπερ καὶ τοὺς καθόλου ζητοῦμεν λόγους, καὶ ἐφʼ ὧν ἐφαρμόττειν οἰόμεθα δεῖν αὐτούς.
But we must grasp this not only by reason, but also in the case of particular and sensible things, for the sake of which we also seek universal theories, and on which we think those theories must apply.
φανερὸν γὰρ καὶ ἐπὶ τούτων ὅτι ἀδύνατον κινεῖσθαι μηδενὸς ἠρεμοῦντος, πρῶτον μὲν οὖν ἐν αὐτοῖς τοῖς ζῴοις·
For it is clear also in the case of these things that it is impossible to move if nothing is at rest, and first of all in the animals themselves.
δεῖ γάρ, ἂν κινῆταί τι τῶν μορίων, ἠρεμεῖν τι· καὶ διὰ τοῦτο αἱ καμπαὶ τοῖς ζῴοις εἰσίν.
For if any of the parts is to move, something must be at rest; and for this reason animals have joints.
ὥσπερ γὰρ κέντρῳ χρῶνται ταῖς καμπαῖς, καὶ γίνεται τὸ ὅλον μέρος, ἐν ᾧ ἡ καμπή, καὶ ἓν καὶ δύο, καὶ εὐθὺ καὶ κεκαμμένον, μεταβάλλον δυνάμει καὶ ἐνεργείᾳ διὰ τὴν καμπήν.
For they use the joints as a center, and the whole part in which the joint is becomes both one and two, both straight and bent, changing potentially and actually because of the joint.
καμπτομένου δὲ καὶ κινουμένου τὸ μὲν κινεῖται σημεῖον τὸ δὲ μένει τῶν ἐν ταῖς καμπαῖς, ὥσπερ ἂν εἰ τῆς διαμέτρου ἡ μὲν Α καὶ ἡ ∠ μένοι, ἡ δὲ Β κινοῖτο, καὶ γίνοιτο ἡ ΑΓ. ἀλλ᾿ ἐνταῦθα μὲν δοκεῖ πάντα τρόπον ἀδιαίρετον εἶναι τὸ κέντρον (καὶ γὰρ τὸ κινεῖσθαι, ὡς φασί, πλάττουσιν ἐπʼ αὐτῶν·
And when it is bent and moved, one of the points in the joints moves while the other remains still, just as if, of the diameter, A and D were to remain still, and B were to move, and AC were to be produced.
οὐ γὰρ κινεῖσθαι τῶν μαθηματικῶν οὐδέν), τὰ δʼ ἐν ταῖς καμπαῖς δυνάμει καὶ ἐνεργείᾳ γίνεται ὁτὲ μὲν ἓν ὁτὲ δὲ διαιρετά.
But whereas in that case the center seems to be indivisible in every way (for they fictitiously attribute movement, as they say, to them; for none of the mathematical objects moves), the points in the joints become potentially and actually at one time one and at another time divisible.
ἀλλ᾿ οὖν ἀεὶ ἡ ἀρχὴ ἡ πρὸς ὅ,ᾗ ἀρχή, ἠρεμεῖ κινουμένου τοῦ μορίου τοῦ κάτωθεν, οἷον τοῦ μὲν βραχίονος κινουμένου τὸ ὠλέκρανον, ὅλου δὲ τοῦ κώλου ὁ ὦμος, καὶ τῆς μὲν κνήμης τὸ γόνυ, ὅλου δὲ τοῦ σκέλους τὸ ἰσχίον.
But at all events, the principle in relation to which it is a principle always remains at rest while the part below moves; for instance, the elbow remains at rest when the forearm moves, the shoulder when the whole limb moves, the knee when the shin moves, and the hip when the whole leg moves.
ὅτι μὲν οὖν καὶ ἐν αὐτῷ ἕκαστόν τι δεῖ -ἔχειν ἠρεμοῦν, ὅθεν ἡ ἀρχὴ τοῦ κινουμένου ἔσται, καὶ πρὸς ὃ ἀπερειδόμενον καὶ ὅλον ἀθρόον κινηθήσεται καὶ κατὰ μέρος, φανερόν.
It is clear, therefore, that each animal must have within itself something at rest, from which the principle of that which is moved will arise, and leaning against which it will be moved both as a whole all at once and in parts.
§22 Ἀλλὰ πᾶσα ἡ ἐν αὐτῷ ἠρεμία ὅμως ἄκυρος, ἂν μή τι ἔξωθεν ἀπλῶς ἠρεμοῦν καὶ ἀκίνητον.
2 But all the rest within the animal is nevertheless ineffective, unless there is something outside that is absolutely at rest and unmoved.
ἄξιον δʼ ἐπιστήσαντας ἐπισκέψασθαι περὶ τοῦ λεχθέντος· ἔχει γὰρ τὴν θεωρίαν οὐ μόνον ὅσον ἐπὶ τὰ ζῷα συντείνουσαν, ἀλλὰ καὶ πρὸς τὴν τοῦ παντὸς κίνησιν καὶ φοράν.
And it is worth pausing to investigate what has been said; for the inquiry into this is relevant not only to animals, but also to the movement and translation of the whole universe.
ὥσπερ γὰρ καὶ ἐν αὐτῷ δεῖ τι ἀκίνητον εἶναι, εἰ μέλλει κινεῖσθαι, οὕτως ἔτι μᾶλλον ἔξω δεῖ τι εἶναι τοῦ ζῴου ἀκίνητον, πρὸς ὃ ἀπερειδόμενον κινεῖται τὸ κινούμενον.
For just as there must be something unmoved within the animal itself, if it is to move, so even more there must be something unmoved outside the animal, leaning against which that which is moved moves.
εἰ γὰρ ὑποδώσει ἀεί, οἷον τοῖς ἑμύσι τοῖς ἐν τῇ γῇ, ἢ τοῖς ἐν τῇ ἄμμῳ πορευομένοις, οὐ πρόεισιν, οὐδʼ ἔσται οὔτε πορεία, εἰ μὴ ἡ γῆ μένοι, οὔτε πτῆσις ἢ νεῦσις, εἰ μὴ ὁ ἀὴρ ἢ ἡ θάλαττα ἀντερείδοι.
For if it always gives way, as in the case of pond-turtles in the mud, or those walking in the sand, it will not advance, nor will there be either walking, unless the earth remains still, or flight or swimming, unless the air or the sea offers resistance.
ἀνάγκη δὲ τοῦτο ἕτερον εἶναι τοῦ κινουμένου, καὶ ὅλον ὅλου, καὶ μόριον μηδὲν εἶναι τοῦ κινουμένου τὸ οὕτως ἀκίνητον· εἰ δὲ μή, οὐ κινηθήσεται.
And it is necessary that this which is thus unmoved be different from that which is moved, and as a whole from a whole, and be no part of that which is moved; otherwise, it will not move.
μαρτύριον δὲ τούτου τὸ ἀπορούμενον, διὰ τί ποτε τὸ πλοῖον ἔξωθεν μέν, ἄν τις ὠθῇ τῷ κοντῷ τὸν ἱστὸν ἢ τι ἄλλο προσβάλλων μόριον, κινεῖ ῥᾳδίως, ἐὰν δʼ ἐν αὐτῷ τις ὢν τῷ πλοίῳ τοῦτο πειρᾶται πράττειν, οὐκ ἂν κινήσειεν οὐδʼ ἂν ὁ Τιτυὸς οὔθʼ ὁ Βορέας πνέων ἔσωθεν ἐκ τοῦ πλοίου, εἰ τύχοι πνέων τὸν τρόπον τοῦτον ὅνπερ οἱ γραφεῖς ποιοῦσιν· ἐξ αὑτοῦ γὰρ τὸ πνεῦμα ἀφιέντα γράφουσιν.
Evidence of this is the puzzle: why is it that if someone from the outside pushes the mast with a pole or applies force to some other part, he moves the boat easily, but if someone being in the boat itself tries to do this, he would not move it, not even if Tityus or Boreas were blowing from inside the boat, if he happened to blow in the manner that painters depict him; for they paint him emitting the breath from himself.
ἐάν τε γὰρ ἠρέμα ῥιπτῇ τὸ πνεῦμά τις ἐάν τʼ ἰσχυρῶς οὕτως ὥστʼ ἄνεμον ποιεῖν τὸν μέγιστον, ἐάν τε ἄλλο τι τὸ ῥιπτούμενον ἢ ὠθούμενον, ἀνάγκη πρῶτον μὲν πρὸς ἠρεμοῦν τι τῶν αὑτοῦ μορίων ἀπερειδόμενον ὠθεῖν, εἶτα πάλιν τοῦτο τὸ μόριον, ἢ αὐτὸ ἢ οὗ τυγχάνει μόριον ὄν, πρὸς τῶν ἔξωθέν τι ἀποστηριζόμενον μένειν.
For whether one blows gently or so strongly as to make the greatest wind, or whether that which is thrown or pushed is something else, it is necessary first to push by leaning against one of one’s own parts that is at rest, and then again this part, either itself or that of which it happens to be a part, must remain still by being supported against something of the external things.
ὁ δὲ τὸ πλοῖον ὠθῶν ἐν τῷ πλοίῳ αὐτὸς ὢν καὶ ἀποστηριζόμενος πρὸς τὸ πλοῖον εὐλόγως οὐ κινεῖ τὸ πλοῖον διὰ τὸ ἀναγκαῖον εἶναι πρὸς ὃ ἀποστηρίζεται μένειν· συμβαίνει δʼ αὐτῷ τὸ αὐτὸ ὅ τε κινεῖ καὶ πρὸς ὃ ἀποστηρίζεται.
But he who pushes the boat, being himself in the boat and supporting himself against the boat, reasonably does not move the boat, because it is necessary that that against which he supports himself remains still; and for him, that which moves and that against which he supports himself happen to be the same thing.
ἔξωθεν δʼ ὠθῶν ἢ ἕλκων κινεῖ· οὐθὲν γὰρ μέρος ἡ γῆ τοῦ πλοίου.
But pushing or pulling from the outside moves it; for the earth is no part of the boat.