[1] Soph. El. i. p. 165, a. 21, 28, 32: ἔστι γὰρ ἡ σοφιστικὴ φαινομένη σοφία οὖσα δ’ οὔ, καὶ ὁ σοφιστὴς χρηματιστὴς ἀπὸ φαινομένης σοφίας ἀλλ’ οὐκ οὔσης· — ἀνάγκη οὖν τοὺς βουλομένους σοφιστεύειν τὸ τῶν εἰρημένων λόγων γένος ζητεῖν· — ὅτι μὲν οὖν ἔστι τι τοιοῦτον λόγων γένος, καὶ ὅτι τοιαύτης ἐφίενται δυνάμεως οὓς καλοῦμεν σοφιστάς, δῆλον. Also xi. p. 171, b. 27.
The Sophistical Elenchus or Refutation, being a delusive semblance of refutation which imposes on ordinary men and induces them to accept it as real, cannot be properly understood without the theory of Elenchus in general; nor can this last be understood without the entire theory of the Syllogism, since the Elenchus is only one variety of Syllogism.[2] The Elenchus is a syllogism with a conclusion contradictory to or refutative of some enunciated thesis or proposition. Accordingly we must first understand the conditions of a good and valid Syllogism, before we study those of a valid Elenchus; these last, again, must be understood, before we enter on the distinctive attributes of the Pseudo-elenchus — the sophistical, invalid, or sham, refutation. In other words, an enumeration and classification of Fallacies forms the closing section of a treatise on Logic — according to the philosophical arrangement originating with Aristotle, and copied by most logicians after him.
[2] Ibid. x. p. 171, a. 1-5.
Aristotle begins by distinguishing reality and mere deceptive appearance; and by stating that this distinction is found to prevail not less in syllogisms than in other matters. Next he designates a notorious class of persons, called Sophists, who made it their profession to study and practise the deceptive appearance of syllogizing; and he then proceeds to distinguish four species of debate:— (1) Didactic; (2) Dialectic; (3) Peirastic; (4) Eristic or Sophistic.[3] In this quadruple arrangement, however, he is not consistent with his own definitions, when he ranks the four as distinct and co-ordinate species. The marked and special antithesis is between Didactic and Dialectic. Both Peirastic and Eristic fall as varieties or sub-species under the species Dialectic; and there is under the species Didactic a variety called Pseudo-graphic or Pseudo-didactic, which stands to Didactic in the same relation in which Eristic stands to Dialectic.[4]
[3] Soph. El. ii. p. 165, a. 38: ἔστι δὴ τῶν ἐν τῷ διαλέγεσθαι λόγων τέτταρα γένη, διδασκαλικοὺ καὶ διαλεκτικοὶ καὶ πειραστικοὶ καὶ ἐριστικοί.
[4] Ibid. xi. p. 171, b. 34.
Didactic discourse is not applicable to all matters indiscriminately, but only to certain special sciences; each of which has its own separate, undemonstrable principia, from which its conclusions, so far as true and valid, must be deduced. It supposes a teacher acquainted with these principia and deductions, talking with some one who being ignorant of them wishes to learn. The teacher puts questions, to which the learner makes the best answers that he can; and, if the answers are wrong, corrects them and proceeds to draw, according to syllogistic canons, conclusions from premisses which he himself knows to be the truth. These premisses the learner must believe upon the teacher’s authority. Properly speaking, indeed, the didactic process is not interrogative (in the same sense that Dialectic is): the teacher does not accept the learner’s answer and reason from it, if he thinks it wrong.[5]
[5] Ibid. xi. p. 172, a. 11: νῦν δ’ οὐκ ἔστιν ὁ διαλεκτιὸς περὶ γένος τι ὡρισμένον, οὐδὲ δεικτικὸς οὐδενός, οὐδὲ τοιοῦτος οἷος ὁ καθόλου. οὔτε γάρ ἐστιν ἅπαντα ἐν ἑνί τινι γένει, οὔτε εἰ εἴη, οἷόν τε ὑπὸ τὰς αὐτὰς ἀρχὰς εἶναι τὰ ὄντα. ὥστ’ οὐδεμία τέχνη τῶν δεικνυουσῶν τινὰ φύσιν ἐρωτητική ἐστιν· οὐ γὰρ ἔξεστιν ὁποτερονοῦν τῶν μορίων δοῦναι· συλλογισμὸς γὰρ οὐ γίνεται ἐξ ἀμφοῖν. ἡ δὲ διαλεκτικὴ ἐρωτηρική ἐστιν· εἰ δ’ ἐδείκνυεν, εἰ καὶ μὴ πάντα, ἀλλὰ τά γε πρῶτα καὶ τὰς οἰκείας ἀρχάς, οὐκ ἂν ἠρώτα. μὴ διδόντος γὰρ οὐκ ἂν ἔτι εἶχεν ἐξ ὧν ἔτι διαλέξεται πρὸς τὴν ἔνστασιν.
When Aristotle, therefore, reckons λόγους διδασκαλικούς as one of the four species τῶν ἐν τῷ διαλέγεσθαι λόγων (Soph. El. ii. p. 165, a. 38), we must understand τὸ διαλέγεσθαι in a very wide and vague sense, going much beyond the derivative noun διαλεκτική.
Dialectic, on the contrary, is applicable to all matters universally and indiscriminately, including even the undemonstrable principia which the teacher assumes as the highest premisses of his didactic syllogisms. It supposes, in place of teacher and learner, an interrogator (or opponent) and a respondent. The respondent declares a problem or thesis, which he undertakes to defend; while the other puts questions to him respecting it, with the purpose of compelling him either to contradict the thesis, or to contradict himself on some other point. The interrogator is allowed only to ask questions, and to deduce legitimate conclusions from the premisses granted by the respondent in answer: he is not permitted to introduce any other premisses. The premisses upon which the debate turns are understood all to be probable — opinions accredited either among an ordinary multitude or among a few wise men, but to have no higher authority. Accordingly there is often a conflict of arguments pro and con, much diversified. The process is essentially controversial; and, if the questioner does not succeed in exposing a contradiction, the respondent is victorious, and remains in possession of the field.