Early Greek Philosophy by John Burnet, with Burnet's notes
177. Relation to Ionic Cosmology 179. The Weight of the Atoms

From Chapter IX., Leukippos of Miletos

178. The Eternal Motion
Leukippos represented the atoms as having been always in motion. Aristotle puts this in his own way. The atomists, he says, "indolently" left it unexplained what was the source of motion, and did not say what sort of motion it was. In other words, they did not decide whether it was a "natural motion" or impressed on them "contrary to their nature."29 He even said that they made it "spontaneous," a remark which has given rise to the erroneous view that they held it was due to chance.30 Aristotle does not say that, however; but only that the atomists did not explain the motion of the atoms in any of the ways in which he himself explained the motion of the elements. They neither ascribed to them a natural motion like the circular motion of the heavens and the rectilinear motion of the four elements in the sublunary region, nor did they give them a forced motion contrary to their own nature, like the upward motion that may be given to the heavy elements and the downward that may be given to the light. The only fragment of Leukippos which has survived is an express denial of chance. "Naught happens for nothing," he said, "but everything from a ground and of necessity."31

Speaking historically, all this means that Leukippos did not, like Empedokles and Anaxagoras, find it necessary to assume a force to originate motion. He had no need of Love and Strife or Mind, and the reason is clear. Though Empedokles and Anaxagoras had tried to explain multiplicity and motion, they had not broken so radically as Leukippos with the Parmenidean One. Both started with a condition of matter in which the "roots" or "seeds" were mixed so as to be "all together," and they therefore required something to break up this unity. Leukippos, who started with an infinite number of Parmenidean "Ones," so to speak, required no external agency to separate them. What he had to do was just the opposite. He had to account for their coming together, and there was nothing so far to prevent his return to the old idea that motion does not require any explanation at all.32

This, then, is what seems to follow from the criticisms of Aristotle and from the nature of the case; but it is not consistent with Zeller's opinion that the original motion of the atoms is a fall through infinite space, as in the system of Epicurus. This view depends, of course, on the further belief that the atoms have weight, and that weight is the tendency of bodies to fall, so we must now consider whether and in what sense weight is a property of the atoms.

Burnet's Notes


29. Arist. Phys. Θ6, 1. 252 a 32 (R. P. 195 a); De caelo, Γ, 2. 300 b 8 (R. P. 195); Met. A, 4. 985 b19 (R. P. ib.).

30. Arist. Phys. B, 4. 196 a 24 (R. P. 195 d). Cicero, De nat. d. i. 66 (R. P. ib.). The latter passage is the source of the phrase "fortuitous concourse" (concurrere=συντρέχειν).

31. Aet. i. 25, 4 (Dox. p. 321), Λεύκιππος πάντα κατ' ἀνάγκην, τὴν δ' αὐτὴν ὑπάρχειν εἱμαρμένην. λέγει γὰρ ἐν τῷ Περὶ νοῦ· Οὐδὲν χρῆμα μάτην γίγνεται, ἀλλὰ πάντα ἐκ λόγου τε καὶ ὑπ' ἀνάγκης.

32. Introd. § VIII.

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