In this chapter Aristotle distinguishes powers belonging to things, from powers belonging to persons — powers irrational from powers rational — powers in which the agent acts without any will or choice, from those in which the will or choice of the agent is one item of the aggregate of conditions. He here expressly recognises that the power of the agent, separately considered, is only conditional; that is, conditional on the presence and suitable state of the patient, as well as upon the absence of counteracting circumstances. But he contends that such absence of counteracting circumstances is plainly implied, and need not be expressly mentioned in the definition.
ἐπεὶ δὲ τὸ δυνατὸν τὶ δυνατὸν καὶ ποτὲ καὶ πῶς καὶ ὅσα ἄλλα ἀνάγκη προσεῖναι ἐν τῷ διορισμῷ —
τὸ δυνατὸν κατὰ λόγον ἅπαν ἀνάγκη, ὅταν ὀρέγηται, οὖ τ’ ἔχει τὴν δύναμιν καὶ ὡς ἔχει, τοῦτο ποιεῖν· ἔχει δὲ παρόντος τοῦ παθητικοῦ καὶ ὡδὶ ἔχοντος ποιεῖν· εἰ δὲ μή, ποιεῖν οὐ δυνήσεται. τὸ γὰρ μηθενὸς τῶν ἕξω κωλύοντος προσδιορίζεσθαι, οὐθὲν ἔτι δεῖ· τὴν γὰρ δύναμιν ἔχει ὥς ἔστι δύναμις τοῦ ποιεῖν, ἔστι δ’ οὐ πάντως, ἀλλ’ ἐχόντων πῶς, ἐν οἷς ἀφορισθήσεται καὶ τὰ ἕξω κωλύοντα· ἀφαιρεῖται γὰρ ταῦτα τῶν ἐν τῷ διορισμῷ προσόντων ἔνια. The commentary of Alexander Aphr. upon this chapter is well worth consulting (pp. 546-548 of the edition of his commentary by Bonitz, 1847). Moreover Aristotle affirms in this chapter, that when τὸ ποιητικὸν and τὸ παθητικὸν come together under suitable circumstances, the power will certainly pass into act.
Here then, it seems to me, Aristotle concedes the doctrine which the Megarics affirmed; or, if there be any difference between them, it is rather verbal than real. In fact, Aristotle’s reasoning in the third chapter (wherein he impugns the doctrine of the Megarics), and the definition of δυνατὸν which he gives in that chapter (1047, a. 25), are hardly to be reconciled with his reasoning in the fifth chapter. Bonitz (Notes on the Metaphys. pp. 393-395) complains of the mira levitas of Aristotle in his reasoning against the Megarics, and of his omitting to distinguish between Vermögen and Möglichkeit. I will not use so uncourteous a phrase; but I think his refutation of the Megarics is both unsatisfactory and contradicted by himself. I agree with the following remark of Bonitz:—“Nec mirum, quod Megarici, aliis illi quidem in rebus arguti, in hâc autem satis acuti, existentiam τῷ δυνάμει ὄντι tribuere recusarint,” &c.
Diodôrus Kronus — his doctrine about τὸ δυνατόν.
The doctrine which I have just been canvassing is expressly cited by Aristotle as a Megaric doctrine, and was therefore probably held by his contemporary Eubulidês. From the pains which Aristotle takes (in the ‘De Interpretatione’ and elsewhere) to explain and vindicate his own doctrine about the Potential and the Actual, we may see that it was a theme much debated among the dialecticians of the day. And we read of another Megaric, Diodorus[60] Kronus, perhaps contemporary (yet probably a little later than Aristotle), as advancing a position substantially the same as that of Eubulidês. That alone is possible (Diodorus affirmed) which either is happening now, or will happen at some future time. As in speaking about facts of an unrecorded past, we know well that a given fact either occurred or did not occur, yet without knowing which of the two is true — and therefore we affirm only that the fact may have occurred: so also about the future, either the assertion that a given fact will at some time occur, is positively true, or the assertion that it will never occur, is positively true: the assertion that it may or may not occur some time or other, represents only our ignorance, which of the two is true. That which will never at any time occur, is impossible.
[60] The dialectic ingenuity of Diodorus is powerfully attested by the verse of Ariston, applied to describe Arkesilaus (Sextus Emp. Pyrrh. Hyp. i. p. 234):
| Πρόσθε Πλάτων, ὄπιθεν Πύῤῥων, μέσσος Διόδωρος. |