178. 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 they did not say what sort of motion it was. In other words, they did not decide whether it was a “natural motion” or one impressed on them “contrary to their nature.”[952] He even went so far as to say that they made it “spontaneous,” a remark which has given rise to the erroneous view that they held it was due to chance.[953] 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 which may be given to the heavy elements and the downward which 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.”[954] Footnote 952: Arist. _Phys._ Θ, 1. 252 a 32 (R. P. 195 a); _de Caelo_, Γ, 2. 300 b 8 (R. P. 195); _Met._ Α, 4. 985 b 19 (R. P. _ib._). Footnote 953: Arist. _Phys._ Β, 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). Footnote 954: 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. If we put the matter 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 did with the Parmenidean One. Both of them 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 give an explanation of their coming together, and there was nothing so far to prevent his return to the old and natural idea that motion does not require any explanation at all.[955] Footnote 955: Introd. § VIII.