See, respecting the different notions of Cause held by ancient philosophers, my remarks on the Platonic Phædon infrà, vol. ii. [ch. xxv].
[65] Aristot. Metaph. E. 1027, a. 13; A. 1071, a. 10.
ὥστε ἡ ὕλη ἔσται αἰτία, ἡ ἐνδεχομέν ἠ παρὰ τὸ ὡς ἐπὶ το πολὺ ἄλλως τοῦ συμβεβηκότος.
Matter is represented as the principle of irregularity, of τὸ ὁπότερ’ ἔτυχε — as the δύναμις τῶν ἐναντίων.
In the explanation given by Alexander of Aphrodisias of the Peripatetic doctrine respecting chance — free-will, the principle of irregularity — τύχη is no longer assigned to the material cause, but is treated as an αἰτία κατὰ συμβεβηκός, distinguished from αἰτία προηγούμενα or καθ’ αὑτά. 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 τὸ δυνατὸν and τὸ ἀδύνατον 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 καθ’ εἱμαρμένην. 2. Or all events do not happen καθ’ εἱμαρμένην, but some events are ἐφ’ ἡμῖν. See De Fato, p. 14 seq. This way of putting the question is directed more against the Stoics, who were the great advocates of εἱμαρμένη, 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 τα καθ’ εἱμαρμένην — τὰ ἐφ’ ἡμῖν is different from the antithesis conceived by Aristotle and does not touch the question about the universality of regular sequence. Τὰ ἐφ’ ἡμῖν describes those sequences in which human volition forms one among the appreciable conditions determining or modifying the result; τὰ καθ’ εἱμαρμένην includes all the other sequences wherein human volition has no appreciable influence. But the sequence τῶν ἐφ’ ἡμῖν is just as regular as the sequence τῶν καθ’ εἱμαρμένην: both the one and the other are often imperfectly predictable, because our knowledge of facts and power of comparison is so imperfect.
Theophrastus discussed τὸ καθ’ εἱμαρμένην, and explained it to mean the same as τὸ κατὰ φύσιν. φανερώτατα δὲ Θεόφραστος δείκνυσι ταὐτὸν ὃν τὸ καθ’ εἱμαρμένην τῷ κατὰ φύσιν (Alexander Aphrodisias ad Aristot. De Animâ, ii.).
Conclusion of Diodôrus — defended by Hobbes — Explanation given by Hobbes.
In what manner Diodorus stated and defended his opinion upon this point, we have no information. We know only that he placed affirmations respecting the future on the same footing as affirmations respecting the past: maintaining that our potential affirmation — May or May not be — respecting some future event, meant no more than it means respecting some past event, viz.: no inherent indeterminateness in the future sequence, but our ignorance of the determining conditions, and our inability to calculate their combined working.[66] In regard to scientific method generally, this problem is of the highest importance: for it is only so far as uniformity of sequence prevails, that facts become fit matter for scientific study.[67] Consistently with the doctrine of all-pervading uniformity of sequence, the definition of Hobbes gives the only complete account of the Impossible and Possible: i.e. an account such as would appear to an omniscient calculator, where May or May not merge in Will or Will not. According as each person falls short of or approaches this ideal standard — according to his knowledge and mental resource, inductive and deductive — will be his appreciation of what may be or may not be — as of what may have been or may not have been during the past. But such appreciation, being relative to each individual mind, is liable to vary indefinitely, and does not admit of being embodied in one general definition.
[66] The same doctrine as that of the Megaric Diodorus is declared by Hobbes in clear and explicit language (First Grounds of Philosophy, ii. 10, 4-5):—“That is an impossible act, for the production of which there is no power plenary. For seeing plenary power is that in which all things concur which are requisite for the production of an act, if the power shall never be plenary, there will always be wanting some of those things, without which the act cannot be produced. Wherefore that act shall never be produced: that is, that act is impossible. And every act, which is not impossible, is possible. Every act therefore which is possible, shall at some time or other be produced. For if it shall never be produced, then those things shall never concur which are requisite for the production of it; wherefore the act is impossible, by the definition; which is contrary to what was supposed.