Aristotle thus draws a broad and marked line between Dialectic on the one hand, and Eristic or Sophistic on the other; and he treats the whole important doctrine of Logical Fallacies as coming under this latter department. The distinction that he draws between them is two-fold: first as to purpose, next as to subject-matter. On the part of the litigious or sophistical debater there is the illicit purpose of victory at all cost, or for profit; and probabilities merely apparent — such as any one may see not to be real probabilities — constitute the matter of his syllogisms.
Now, as to the distinction of purpose, we may put aside the idea of profit as having no essential connection with the question. It is quite possible to suppose the fair Dialectician, not less than the Sophist, as exhibiting his skill for pecuniary reward; while the eagerness for victory on both sides is absolutely indispensable even in well-conducted debate, in order that the appropriate stimulus and benefit of dialectical exercise may be realized. But, if the distinction of purpose and procedure, between the Dialectician and the Sophist, is thus undefined and unsatisfactory, still more unsatisfactory is the distinction of subject-matter. To discriminate between what is really probable (i.e., accredited either by the multitude or by a wise few), and what is only probable in appearance and not in reality — is a task of extreme difficulty. The explanation given by Aristotle himself[19] — when he describes the apparently probable as that which has only superficial show, and which the most ordinary intelligence discerns at once to be false — includes only the more gross and obvious fallacies, but leaves out all the rest. Nothing can be more incorrect than the assumption, in regard to fallacies generally, that the appearance of probability is too faint to impose upon any ordinary man. If all fallacies could be supposed to come under this definition, the theory of Fallacies would undoubtedly be worthless (as Mr. Poste suggests that it is, in the Preface to his translation of the Sophistici Elenchi); and the most dishonest Sophist would at any rate be harmless. But, in fact, Aristotle himself departs from this definition even in the beginning of the Sophistici Elenchi; for he there treats the sophistic syllogism and refutation as having a semblance of validity plausible enough to impose upon many persons, and to be difficult of detection; like base metals having the exterior appearance of gold and silver, and like men got up for the purpose of looking finer and stronger than they really are.[20] Here we have the eristic or sophistic syllogism presented as fallacious, yet as very likely to be mistaken for truth, by unprepared auditors, unless warning and precaution be applied; not (as it was set forth in the definition above cited) as bearing the plain and obvious stamp of falsehood, recognizable even by the vulgar. At the time when Aristotle constructed that definition, he probably had present to his mind such caricatures of dialectical questions as Plato (in the dialogue Euthydêmus) puts into the mouth of the Sophists Euthydêmus and Dionysodorus. And, since Aristotle chose to connect fallacious reasoning with dishonest purposes, and to announce it as employed exclusively by dishonest debaters, he seems to have found satisfaction in describing it as something which no honest man of ordinary understanding could accept as true: the Sophist being thus presented not merely as a knave but as a fool.
[19] Topic. I. i. p. 100, b. 24, seq.
[20] Soph. El. i. p. 164, a. 23-b. 27. τὸν αὐτὸν δὲ τρόπον καὶ συλλογισμὸς καὶ ἔλεγχος ὁ μὲν ἔστιν, ὁ δ’ οὐκ ἔστι μέν, φαίνεται δὲ διὰ τὴν ἀπειρίαν· οἱ γὰρ ἄπειροι ὥσπερ ἂν ἀπέχοντες πόῤῥωθεν θεωροῦσιν.
I think it a mistake on the part of Aristotle to treat the fallacies incidental to the human intellect as if they were mere traps laid by Sophists and litigants; and as if they would never show themselves, assuming dialectical debate to be conducted entirely with a view to its legitimate purposes of testing a thesis and following out argumentative consequences. It is true that, if there are infirmities incident to the human intellect, a dishonest disputant will be likely to take advantage of them. So far it may be well to note his presence. But the dishonest disputant does not originate these infirmities: he finds them already existing, and manifested undesignedly not merely in dialectical debate, but even in ordinary discourse. It is the business of those who theorize on the intellectual processes to specify and discriminate the Fallacies as liabilities to intellectual error among mankind in general, honest or dishonest, with a view to precaution against their occurrence, or correction if they do occur; not to present them as inventions of a class of professional cheats,[21] or as tares sown by the enemy in a field where the natural growth would be nothing but pure wheat.
[21] Soph. El. i. p. 165, a. 19, seq.
In point of fact the actual classification of Fallacies given by Aristotle is far sounder than his announcement would lead us to expect. Though he entitles them Sophistical Refutations, describing them as intentionally cultivated and exclusively practised by professional Sophists for gain, or by unprincipled litigants for victory, yet he recognises them as often very difficult of detection, and as an essential portion of the theory of Dialectic generally.[22] The various general heads under which he distributes them are each characterized by intellectual or logical marks.
[22] Ibid. xi. p. 172, b. 7.
His first and most general observation is, that language is the usual medium and instrument through which fallacies are operated.[23] Names and propositions are of necessity limited in number; but things named or nameable are innumerable; hence it happens inevitably that the same name or the same proposition must have several different meanings. Since we cannot talk of things except by means of their names, the equivocation inseparable from these names is a constant source of false conclusions.[24]
[23] Ibid. i. p. 165, a. 5.