In the explanation given by Alexander of Aphrodisias of the Peripatetic doctrine respecting chance--free-will, the principle of irregularity--[Greek: tu/chê] is no longer assigned to the material cause, but is treated as an [Greek: ai)ti/a kata\ sumbebêko/s], distinguished from [Greek: ai)ti/a proêgou/mena] or [Greek: kath' au(ta/]. The exposition given of the doctrine by Alexander is valuable and interesting. See his treatise De Fato, addressed to the Emperor Severus, in the edition of Orelli, Zurich. 1824 (a very useful volume, containing treatises of Ammonius, Plotinus, Bardesanes, &c., on the same subject); also several sections of his Quæstiones Naturales et Morales, ed. Spengel, Munich, 1842, pp. 22-61-65-123, &c. He gives, however, a different explanation of [Greek: to\ dunato\n] and [Greek: to\ a)du/naton] in pp. 62-63, which would not be at variance with the doctrine of Diodorus. We may remark that Alexander puts the antithesis of the two doctrines differently from Aristotle,--in this way. 1. Either all events happen [Greek: kath' ei(marme/nên]. 2. Or all events do not happen [Greek: kath' ei(marme/nên], but some events are [Greek: e)ph' ê(mi=n]. See De Fato, p. 14 seq. This way of putting the question is directed more against the Stoics, who were the great advocates of [Greek: ei(marme/nê], than against the Megaric Diodorus. The treatises of Chrysippus and the other Stoics alter both the wording and the putting of the thesis. We know that Chrysippus impugned the doctrine of Diodorus, but I do not see how. The Stoic antithesis of [Greek: ta kath' ei(marme/nên--ta\ e)ph' ê(mi=n] is different from the antithesis conceived by Aristotle and does not touch the question about the universality of regular sequence. [Greek: Ta\ e)ph' ê(mi=n] describes those sequences in which human volition forms one among the appreciable conditions determining or modifying the result; [Greek: ta\ kath' ei(marme/nên] includes all the other sequences wherein human volition has no appreciable influence. But the sequence [Greek: tô=n e)ph' ê(mi=n] is just as regular as the sequence [Greek: tô=n kath' ei(marme/nên]: both the one and the other are often imperfectly predictable, because our knowledge of facts and power of comparison is so imperfect. Theophrastus discussed [Greek: to\ kath' ei(marme/nên], and explained it to mean the same as [Greek: to\ kata\ phu/sin. phanerô/tata de\ Theo/phrastos dei/knusi tau)to\n o(\n to\ kath' ei(marme/nên tô=| kata\ phu/sin] (Alexander Aphrodisias ad Aristot. De Animâ, ii.).] [Side-note: Conclusion of Diodôrus--defended by Hobbes--Explanation given by Hobbes.]