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Aristotle · Physics §4.8#3

Equal Speed of Bodies and Cube Experiment Refuting Void

Passage 49 of 113 · Greek

Summary

Aristotle points out the absurdity that in a void, because there is no resistance, all bodies regardless of their weight would move at the same speed. Furthermore, through a thought experiment of placing a cube in a void, he demonstrates that a void and the physical bulk of a body would become indistinguishable, thereby rejecting the existence of a separated void.

§4.8#3ᾗ μὲν οὖν διαφέρουσι διʼ ὧν φέρονται, ταῦτα συμβαίνει, κατὰ δὲ τὴν τῶν φερομένων ὑπεροχὴν τάδε·
Now, while these things happen insofar as the media through which things are carried differ, the following happens according to the excess of the carried bodies.
ὁρῶμεν γὰρ τὰ μείζω ῥοπὴν ἔχοντα ἢ βάρους ἢ κουφότητος, ἐὰν τἆλλα ὁμοίως ἔχῃ, θᾶττον φερόμενα τὸ ἴσον χωρίον, καὶ κατὰ λόγον ὃν ἔχουσι τὰ μεγέθη πρὸς ἄλληλα.
For we see that those having a greater impulse of weight or lightness, if other things are in like manner, are carried faster over an equal distance, and in the ratio which their magnitudes have to each other.
ὥστε καὶ διὰ τοῦ κενοῦ.
So that this should happen also through the void.
ἀλλʼ ἀδύνατον· διὰ τίνα γὰρ αἰτίαν οἰσθήσεται θᾶττον;
But this is impossible; for due to what cause will it be carried faster?
ἐν μὲν γὰρ τοῖς πλήρεσιν ἐξ ἀνάγκης· θᾶττον γὰρ διαιρεῖ τῇ ἰσχύϊ τὸ μεῖζον· ἢ γὰρ σχήματι διαιρεῖ, ἢ ῥοπῇ ἣν ἔχει τὸ φερόμενον ἢ τὸ ἀφεθέν, ἰσοταχῆ ἄρα πάντʼ ἔσται.
For in full media, it is of necessity; for the greater body divides the medium faster by its force; for it divides either by its shape, or by the impulse which the body carried or let go has. Therefore, all things will be of equal speed.
ἀλλʼ ἀδύνατον.
But this is impossible.
ὅτι μὲν οὖν εἰ ἔστι κενόν, συμβαίνει τοὐναντίον ἢ διʼ ὃ κατασκευάζουσιν οἱ φάσκοντες εἶναι κενόν, φανερὸν ἐκ τῶν εἰρημένων.
That, therefore, if there is a void, the contrary happens to that for the sake of which those who claim there is a void establish it, is clear from what has been said.
οἱ μὲν οὖν οἴονται τὸ κενὸν εἶναι, εἴπερ ἔσται ἡ κατὰ τόπον κίνησις, ἀποκεκριμένον καθʼ αὑτό· τοῦτο δὲ τοὐτόν ἐστι τῷ τὸν τόπον φάναι εἶναί τι κεχωρισμένον· τοῦτο δʼ ὅτι ἀδύνατον, εἴρηται πρότερον.
For they think that the void, if there is to be motion in place, is something separated by itself; and this is the same as saying that place is something separate; and that this is impossible has been said before.
καὶ καθʼ αὑτὸ δὲ σκοποῦσιν φανείη ἂν τὸ λεγόμενον κενὸν ὡς ἀληθῶς κενόν.
And to those who consider it by itself, the so-called void would appear to be truly void.
ὥσπερ γὰρ ἐὰν ἐν ὕδατι τιθῇ τις κύβον, ἐκστήσεται τοσοῦτον ὕδωρ ὅσος ὁ κύβος, οὕτω καὶ ἐν ἀέρι· ἀλλὰ τῇ αἰσθήσει ἄδηλον.
For just as if one places a cube in water, an amount of water equal to the cube will yield place, so too in air, though it is imperceptible to sense.
καὶ αἰεὶ δὴ ἐν παντὶ σώματι ἔχοντι μετάστασιν, ἐφʼ ὃ πέφυκε μεθίστασθαι, ἀνάγκη, ἂν μὴ συμπιλῆται, μεθίστασθαι ἢ κάτω αἰεί, εἰ κάτω ἡ φορὰ ὥσπερ γῆς, ἢ ἄνω, εἰ πῦρ, ἢ ἐπʼ ἄμφω, ὁποῖον ἄν τι ᾖ τὸ ἐντιθέμενον·
And indeed, in every body that is capable of displacement, it is necessary, in the direction in which it naturally displaces itself, if it is not compressed, to displace itself either always downward, if the motion is downward as that of earth, or upward, if fire, or in both directions, whatever the inserted body may be.
ἐν δὲ δὴ τῷ κενῷ τοῦτο μὲν ἀδύνατον (οὐδὲν γὰρ σῶμα), διὰ δὲ τοῦ κύβου τὸ ἴσον διάστημα διεληλυθέναι, ὅπερ ἦν καὶ πρότερον ἐν τῷ κενῷ, ὥσπερ ἂν εἰ τὸ ὕδωρ μὴ μεθίστατο τῷ ξυλίνῳ κύβῳ μηδʼ ὁ ἀήρ, ἀλλὰ πάντῃ διῇεσαν διʼ αὐτοῦ.
But in the void this is indeed impossible (for there is no body), and [it is necessary] that the equal dimension should have gone through the cube, which was also previously in the void, just as if the water had not displaced itself for the wooden cube, nor the air, but they went through it in every way.
ἀλλὰ μὴν καὶ ὁ κύβος γε ἔχει τοσοῦτον μέγεθος, ὅσον κατέχει κενόν· ὃ εἰ καὶ θερμὸν ἢ ψυχρόν ἐστιν ἢ βαρὺ ἢ κοῦφον, οὐδὲν ἧττον ἕτερον τῷ εἶναι πάντων τῶν παθημάτων ἐστί, καὶ εἰ μὴ χωριστόν· λέγω δὲ τὸν ὄγκον τοῦ ξυλίνου κύβου.
But surely, the cube also has as much magnitude as the void it occupies; which, even if it is hot or cold or heavy or light, is nonetheless different in its being from all these attributes, even if it is not separable; and I mean the bulk of the wooden cube.
ὥστʼ εἰ καὶ χωρισθείη τῶν ἄλλων πάντων καὶ μήτε βαρὺ μήτε κοῦφον εἴη, καθέξει τὸ ἴσον κενὸν καὶ ἐν τῷ αὐτῶ ἔσται τῷ τοῦ τόπου καὶ τῷ τοῦ κενοῦ μέρει ἴσῳ ἑαυτῶ.
So that, even if it were separated from all other things and were neither heavy nor light, it will occupy the equal void and will be in the same part of place and of the void, equal to itself.
τι οὖν διοίσει τὸ τοῦ κύβου σῶμα τοῦ ἴσου κενοῦ καὶ τόπου;
What, then, will the body of the cube differ from the equal void and place?
καὶ εἰ δύο τοιαῦτα, διὰ τί οὐ καὶ ὁποσαοῦν ἐν τῷ αὐτῶ ἔσται;
And if two such things [can be in the same place], why not also any number whatever in the same [place]?
ἓν μὲν δὴ τοῦτο ἄτοπον καὶ ἀδύνατον.
This, then, is one absurdity and impossibility.
ἔτι δὲ φανερὸν ὅτι τοῦτο ὁ κύβος ἕξει καὶ μεθιστάμενος, ὃ καὶ τὰ ἄλλα σώματα πάντʼ ἔχει.
Moreover, it is clear that the cube will have this even when it is displaced, which all other bodies also have.
ὥστʼ εἰ τοῦ τόπου μηδὲν διαφέρει, τί δεῖ ποιεῖν τόπον τοῖς σώμασιν παρὰ τὸν ἑκάστου ὄγκον, εἰ ἀπαθὲς ὁ ὄγκος;
So that, if it differs in nothing from place, why is there need to make a place for bodies besides the bulk of each, if the bulk is unaffected?
οὐδὲν γὰρ συμβάλλεται, εἰ ἕτερον περὶ αὐτὸν ἴσον διάστημα τοιοῦτον εἴη.
For it contributes nothing if there should be another such equal interval around it.
ὅτι μὲν τοίνυν οὐκ ἔστι κεχωρισμένον κενόν, ἐκ τούτων ἐστὶ δῆλον.
That, therefore, there is no separated void is clear from these things.

Notes

  1. 216a13ῥοπὴν ἔχοντα ἢ βάρους ἢ κουφότητος — The genitive phrase ἢ βάρους ἢ κουφότητος (of weight or lightness) modifies ῥοπὴν (impulse, inclination). In Aristotle's theory of motion, this refers to the downward or upward 'impulse' or 'momentum' caused by a body's inherent tendency to move toward its natural place (downward for weight, upward for lightness).
  2. 216a20ἰσοταχῆ ἄρα πάντʼ ἔσται — This is the absurd conclusion (reductio au absurdum) drawn by Aristotle: that in a void, because there is no resistance, all bodies, regardless of their weight or lightness, would move at the same speed. While this proposition anticipates the modern law of falling bodies in a vacuum, Aristotle himself rejects it as an impossibility.
  3. 216a26καθʼ αὑτὸ δὲ σκοποῦσιν — The present participle σκοποῦσιν is in the dative plural ('to those who consider'), referring back to the proponents of the void (οἱ φάσκοντες) or to researchers in general. Alternatively, it can be understood conditionally ('if one considers it by itself'), but here it functions as the dative of interest pointing to the subjects of inquiry.
  4. 216b11τοῦτο ὁ κύβος ἕξει — The referent of the demonstrative pronoun τοῦτο and the relative pronoun ὃ is the 'bulk' (ὄγκος) of the wooden cube under discussion, or its corresponding 'dimension/extension' (διάστημα). It expresses the physical intuition that a body retains its own volume even when it changes its position.

Cite this passage

Aristotle, Physics §4.8#3. Humanitext Reader, https://reader.humanitext.ai/en/text/urn:cts:greekLit:tlg0086.tlg031.humanitext-grc1:4.8%233

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