13. The predicate may belong to its subject either necessarily, or usually, or by pure hazard. You will take notice in which of these three ways the respondent affirms it, and whether that which he chooses is conformable to the fact. If he affirms it as necessary, when it is really either usual or casual, the thesis will be open to your attacks. If he affirms it without clearly distinguishing in which of the three senses he intends it to be understood, you are at liberty to construe it in that one of the three senses which best suits your argument.[105]
[105] Ibid. b. 1-20. This locus seems unsuitable in that part of the Topica where Aristotle professes to deal with theses τοῦ συμβεβηκότος, or theses affirming or denying accidental predicates. It is one of the suppositions here that the respondent affirms the predicate as necessary.
14. Perhaps the thesis may have predicate and subject exactly synonymous, so that the same thing will be affirmed as an accident of itself. On this ground it will be assailable.[106]
[106] Ibid. b. 21-26.
15. Sometimes the thesis will have more than one proposition contrary to it. If so, you may employ in arguing against it that one among its various contraries which is most convenient for your purpose.[107] Perhaps the predicate (accidental) of the thesis may have some contrary: if it has, you will examine whether that contrary belongs to the subject of the thesis; and, should such be the case, you may use it as an argument to refute the thesis itself.[108] Or the predicate of the thesis may be such that, if the thesis be granted, it will follow as a necessary consequence that contrary predicates must belong to the same subject. Thus, if the thesis be that the Platonic Ideas exist in us, it follows necessarily that they are both in motion and at rest; both perceivable by sense, and cogitable by intellect.[109] As these two predicates (those constituting the first pair as well as the second pair) are contrary to each other, and cannot both belong to the same subject, this may be used as an argument against the thesis from which such consequence follows.
[107] Ibid. vii. p. 112, b. 28-p. 113, a. 19. δῆλον οὖν ἐκ τῶν εἰρημένων ὅτι τῷ αὐτῷ πλείονα ἐναντία συμβαίνει γίνεσθαι. — λαμβάνειν οὖν τῶν ἐναντίων ὁπότερον ἂν ᾖ πρὸς τὴν θέσιν χρήσιμον.
[108] Ibid. viii. p. 113, a. 20-23.
[109] Topic. II. viii. p. 113, a. 24-32: ἢ εἴ τι τοιοῦτον εἴρηται κατά τινος, οὗ ὄντος ἀνάγκη τὰ ἐναντία ὑπάρχειν· οἷον εἰ τὰς ἰδέας ἐν ἡμῖν ἔφησεν εἶναι· κινεῖσθαί τε γὰρ καὶ ἠρεμεῖν αὐτὰς συμβήσεται, ἔτι δὲ αἰσθητὰς καὶ νοητὰς εἶναι. Aristotle then proceeds to state how this consequence arises. Those who affirm the Platonic Ideas, assign to them as fundamental characteristic, that they are at rest and cogitable. But, if the Ideas exist in us, they must be moveable, because we are moved; they must also be perceivable by sense, because it is through vision only that we discriminate and know differences of form. Waitz observes (in regard to the last pair, καὶ αἰσθηταί): “Nam singulæ ideæ certam quandam rerum speciem et formam exprimunt: species autem et forma oculis cernitur.â€� I do not clearly see, however, that this is a consequence of affirming Ideas to be ἐν ἡμῖν; it is equally true if they are not ἐν ἡμῖν.
16. We know that whatever is the recipient of one of two contraries, is capable also of becoming recipient of the other. If, therefore, the predicate of the thesis has any contrary, you will examine whether the subject of the thesis is capable of receiving such contrary. If not, you have an argument against the thesis. Let the thesis be, The appetitive principle is ignorant. If this be true, that principle must be capable of knowledge.[110] Since this last is not generally admitted, you have an argument against the thesis.
[110] Topic. II. vii. p. 113, a. 33-b. 10.