The expression used by Empedokles to describe the movement of the elements is that they “run through each other” (fr. 17, 34). Aristotle tells us[595] that he explained mixture in general by “the symmetry of pores.” And this is the true explanation of the “attraction of like for like.” The “pores” of like bodies are, of course, much the same size, and these bodies can therefore mingle easily. On the other hand, a finer body will “run through” a coarse one without becoming mixed, and a coarse body will not be able to enter into the pores of a finer one at all. It will be observed that, as Aristotle says, this really implies something like the atomic theory; but there is no evidence that Empedokles himself was conscious of that. Another question raised by Aristotle is even more instructive. Are the pores, he asks, empty or full? If empty, what becomes of the denial of the void? If full, why need we assume pores at all?[596] These questions Empedokles would have found it hard to answer. They point to a real want of thoroughness in his system, and mark it as a mere stage in the transition from Monism to Atomism. Footnote 595: _Ibid._ Α, 8. 324 b 34 (R. P. 166 h). Footnote 596: Arist. _de Gen. Corr._ 326 b 6. [Sidenote: The four periods.] 110. It will be clear from all this that we must distinguish four periods in the cycle. First we have the Sphere, in which all the elements are mixed together by Love. Secondly, there is the period when Love is passing out and Strife coming in, when, therefore, the elements are partially separated and partially combined. Thirdly, comes the complete separation of the elements, when Love is outside the world, and Strife has given free play to the attraction of like for like. Lastly, we have the period when Love is bringing the elements together again, and Strife is passing out. This brings us back in time to the Sphere, and the cycle begins afresh. Now a world such as ours can exist only in the second and fourth of these periods; and it is clear that, if we are to understand Empedokles, we must discover in which of these we now are. It seems to be generally supposed that we are in the fourth period;[597] I hope to show that we are really in the second, that when Strife is gaining the upper hand. Footnote 597: This is the view of Zeller (pp. 785 sqq.), but he admits that the external testimony, especially that of Aristotle, is wholly in favour of the other. His difficulty is with the fragments, and if it can be shown that these can be interpreted in accordance with Aristotle’s statements, the question is settled. Aristotle was specially interested in Empedokles, and was not likely to misrepresent him on such a point. [Sidenote: Our world the work of Strife.]