[433] Topic. VIII. xi. p. 162, a. 8-11: τοῖς δὲ διὰ ψευδῶν ἀληθὲς συμπεραινομένοις οὐ δίκαιον ἐπιτιμᾶν — φανερὸν δ’ ἐκ τῶν Ἀναλυτικῶν.
When you have obtained your premisses and proved a conclusion, these same premisses will not serve as proof of any other proposition separate and independent of the conclusion; such may sometimes seem to be the case, but it is a mere sophistical delusion. If your premisses are both of them probable, your conclusion may in some cases be more probable than either.[434]
[434] Ibid. a.12-24.
Aristotle here introduces four definitions of terms, which are useful in regard to his thoughts but have no great pertinence in the place where they occur: ἔστι δὲ φιλοσόφημα μὲν συλλογισμὸς ἀποδεικτικός, ἐπιχείρημα δὲ συλλογισμὸς διαλεκτικός, σόφισμα δὲ συλλογισμὸς ἐριστικός, ἀπόρημα δὲ συλλογισμὸς διαλεκτικὸς ἀντιφάσεως.
One other matter yet remains in which your procedure as questioner may be blameable. The premisses through which you prove your conclusion may be long and unnecessarily multiplied; the conclusion may be such that you ought to have obtained it through fewer, yet equally pertinent premisses.[435]
[435] Ibid. a. 24-34.
The example whereby Aristotle illustrates this position is obscure and difficult to follow. It is borrowed from the Platonic theory of Ideas. The point which you are supposed to be anxious to prove is, that one opinion is more opinion than another (ὅτι ἐστὶ δόξα μᾶλλον ἑτέρα ἑτέρας). To prove it you ask as premisses: (1) That the Idea of every class of things is more that thing than any one among the particulars of the class; (2) That there is an Idea of matter of opinion, and that this Idea is more opinion than any one of the particular matters of opinion. If this Idea is more opinion, it must also be more true and accurate than any particular matter of opinion. And it is this last conclusion that Aristotle seems to indicate as the conclusion to be proved: ὥστε αὑτὴ ἡ δόξα ἀκριβεστέρα ἐστίν (a. 32).
As I understand it, Aristotle supposes that the doctrine which you are here refuting is, that all ἔνδοξα are on an equal footing as to truth and accuracy; and that the doctrine which you are proving against it is, that one ἔνδοξον is more true and accurate than another. If you attempt to prove this last by invoking the Platonic theory of Ideas, you will introduce premisses far-fetched and unnecessary, even if true; whereas you might prove your conclusion from premisses easier and more obvious.
The fault is (he says) that such roundabout procedure puts out of sight the real ground of the proof: τίς δὲ ἡ μοχθηρία; ἢ ὅτι ποιεῖ, παρ’ ὃ ὁ λόγος, λανθάνειν τὸ αἴτιον (a. 33). The dubitative and problematical form here is remarkable. How would Aristotle himself have proved the above conclusion? By Induction? He does not tell us.
The cases in which your argument will carry the clearest evidence, impressing itself even on the most vulgar minds, are those in which you obtain such premisses as will enable you to draw your final conclusion without asking any farther concessions. But this will rarely happen. Even after you have obtained all the premisses substantially necessary to your final conclusion, you will generally be forced to draw out two or more prosyllogisms or preliminary syllogisms, and to ask the assent of the respondent to these, before you can venture to enunciate the final conclusion. This second grade of evidence is however sufficient, even if the premisses fall short of the highest probability.[436]