But it is not every problem coming under one of these three heads that is fit for dialectic debate. If a man propounds as subject for debate, Whether we ought to honour the gods or to love our parents, he deserves punishment instead of refutation: if he selects the question, Whether snow is white or not, he must be supposed deficient in perceptive power.[25] What all persons unanimously believe, is unsuitable:[26] what no one believes is also unsuitable, since it will not be conceded by any respondent. The problem must have some doubts and difficulties, in order to afford scope for discussion; yet it must not be one of which the premisses are far-fetched or recondite, for that goes beyond the limits of dialectic exercise.[27] It ought to be one on which opinions are known to be held, both in the affirmative and in the negative; on which either the multitude differ among themselves, the majority being on one side, while yet there is an adverse minority; or some independent authority stands opposed to the multitude, such as a philosopher of eminence, a professional man or artist speaking on his own particular craft, a geometer or a physician on the specialities of his department. Matters such as these are the appropriate subjects for dialectic debate; and new matters akin to them by way of analogy may be imagined and will be perfectly admissible.[28] Even an ingenious paradox or thesis adverse to prevailing opinions may serve the purpose, as likely to obtain countenance from some authority, though as yet we know of none.[29]
[25] Ibid. xi. p. 105, a. 67: κολάσεως — αἰσθήσεως, δέονται. Yet he considers the question, Whether we ought rather to obey the laws of the state or the commands of our parents, in case of discrepancy between the two,-—as quite fit for debate (xiv. p. 105, b. 22).
[26] Ibid. x. p. 104, a. 5.
[27] Ibid. xi. p. 105, a. 7: οὐδὲ δὴ ὧν σύνεγγυς ἡ ἀπόδειξις, οὔδ’ ὧν λίαν πόῤῥω· τὰ μὲν γὰρ οὐκ ἔχει ἀπορίαν, τὰ δὲ πλείον ἢ κατὰ γυμναστικήν. The loose use of the word ἀπόδειξις deserves note here: it is the technical term of the Analyt. Post., denoting that application of the syllogism which contrasts with Dialectic altogether.
Aristotle here means only that problems falling within these limits are the best for dialectic discussion; but, in his suggestions later on, he includes problems for discussion involving the utmost generalities of philosophy. For example, he often adverts to dialectic debate on the Platonic Ideas or Forms (Topic. II. vii. p. 113, a. 25; V. vii. p. 137, b. 7; VI. vi. p. 143, b. 24. Compare also I. xi. p. 104, b. 14.)
[28] Topic. I. x. p. 104, a. 11-37.
[29] Ibid. xi. p. 104, b. 24-28: ἢ περὶ ὧν λόγον ἔχομεν ἐναντίον ταῖς δόξαις — τοῦτο γάρ, εἰ καί τινι μὴ δοκεῖ, δόξειεν ἂν διὰ τὸ λόγον ἔχειν.
These conditions apply both to problems propounded for debate, and to premisses tendered on either side during the discussion. Both the interrogator and the respondent — the former having to put appropriate questions, and the latter to make appropriate answers — must know and keep in mind these varieties of existing opinion among the multitude as well as among the special dissident authorities above indicated. The dialectician ought to collect and catalogue such Endoxa, with the opinions analogous to them, out of written treatises and elsewhere;[30] distributing them under convenient heads, such as those relating to good and evil generally, and to each special class of good, &c. Aristotle, however, admonishes him that he is debating problems not scientifically, but dialectically: having reference not to truth, but to opinion.[31] If the interrogator were proceeding scientifically and didactically, he would make use of all true and ascertained propositions, whether the respondent conceded them or not, as premisses for his syllogism. But in Dialectic he is dependent on the concession of the respondent, and can construct his syllogisms only from premisses that have been conceded to him.[32] Hence he must keep as closely as he can to opinions carrying extrinsic authority, as being those which the respondent will hesitate to disallow.[33]
[30] Topic. I. xiv. p. 105, b. 1-18. ἐκλέγειν δὲ χρὴ καὶ ἐκ τῶν γεγραμμένων λόγων.
[31] Ibid. b. 30: πρὸς μὲν οὖν φιλοσοφίαν κατ’ ἀλήθειαν περὶ αὐτῶν πραγματευτέον, διαλεκτικῶς δὲ πρὸς δόξαν.