may move; the second emphasises the fact that, however slowly it moves, it will traverse an infinite distance.[1]
(3) The arrow in flight is at rest. For, if everything is at rest when it occupies a space equal to itself, and what is in flight at any given moment always occupies a space equal to itself, it cannot move.[2]
Here a further complication is introduced. The moving object itself has length, and its successive positions are not points but lines. The first two arguments are intended to destroy the hypothesis that a line consists of an infinite number of indivisibles; this argument and the next deal with the hypothesis that it consists of a finite[3] number of indivisibles.
(4) Half the time may be equal to double the time. Let us suppose three rows of bodies,[4] one of which (A) is at rest while the other two (B, C) are moving with equal velocity in opposite directions (Fig. 1). By the time they are all in the same part of the course, B will have passed twice as many of the bodies in C as in A (Fig. 2).
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Therefore the time which it takes to pass C is twice as long as the time it takes to pass A. But the time which B and C take
- ↑ As Mr. Jourdain puts it (Mind, 1916, p. 42), "the first argument shows that motion can never begin; the second argument shows that the slower moves as fast as the faster," on the hypothesis that a line is infinitely divisible into its constituent points.
- ↑ Phys. Z, 9, 239 b 30 (R. P. 138); ib. 239 b 5 (R. P. 138 a). The latter passage is corrupt, though the meaning is plain. I have translated Zeller's version of it: εἰ γάρ, φησίν, ἠρεμεῖ πᾶν ὅταν ᾖ κατὰ τὸ ἴσον, ἔστι δ' ἀεὶ τὸ φερόμενον ἐν τῷ νῦν κατὰ τὸ ἴσον, ἀκίνητον κ.τ.λ.. Of course ἀεί means "at any time," not "always," and κατὰ τὸ ἴσον is, literally, "on a level with a space equal (to itself)." For other readings, see Zeller, p. 598 n. 3; and Diels, Vors. 19 A 27.
- ↑ See Jourdain (loc. cit.).
- ↑ The word is ὄγκοι; cf. Chap. VII. p. 291, n. 3. The name is very appropriate for the Pythagorean units, which Zeno had shown to have length, breadth, and thickness (fr. 1).
