[62] Mill, ‘System of Logic,’ Book V., to which is prefixed the following citation from Hobbes’s ‘Logica’. “Errare non modo affirmando et negando, sed etiam in sentiendo, et in tacitâ hominum cogitatione, contingit.”
Mr. Mill points out forcibly both the operation of moral or emotional bias in perverting the intellect, and causing sophisms or fallacies to produce conviction; and the increased chance afforded for the success of a sophism by the suppression of part of the premisses, which is unavoidable in informal discussions.
“Bias is not a direct source of wrong conclusions (v. 1-3). We cannot believe a proposition only by wishing, or only by dreading, to believe it. Bias acts indirectly by placing the intellectual grounds of belief in an incomplete or distorted shape before a man’s eyes. It makes him shrink from the irksome labour of a rigorous induction. It operates too by making him look out eagerly for reasons, or apparent reasons, to support opinions which are conformable, or resist those which are repugnant, to his interests or feelings; and when the interests or feelings are common to great numbers of persons, reasons are accepted or pass current which would not for a moment be listened to in that character, if the conclusion had nothing more powerful than its reasons to speak in its behalf. The natural or acquired prejudices of mankind are perpetually throwing up philosophical theories, the sole recommendation of which consists in the premisses which they afford for proving cherished doctrines, or justifying favourite feelings; and when any one of these theories has become so thoroughly discredited as no longer to serve the purpose, another is always ready to take its place.” — “Though the opinions of the generality of mankind, when not dependent upon mere habit and inculcation, have their root much more in the inclinations than in the intellect, it is a necessary condition to the triumph of the moral bias that it should first pervert the understanding.”
Again in v. 2, 3. “It is not in the nature of bad reasoning to express itself unambiguously. When a sophist, whether he is imposing upon himself or attempting to impose upon others, can be constrained to throw his argument into so distinct a form, it needs, in a large number of cases, no farther exposure. In all arguments, everywhere but in the schools, some of the links are suppressed: à fortiori, when the arguer either intends to deceive, or is a lame and inexpert thinker, little accustomed to bring his reasoning processes to any test; and it is in those steps of the reasoning which are made in this tacit and half-conscious, or even wholly unconscious, manner, that the error oftenest lurks. In order to detect the fallacy the proposition thus silently assumed must be supplied, but the reasoner, most likely, has never really asked himself what he was assuming; his confuter, unless permitted to extort it from him by the Socratic mode of interrogation, must himself judge what the suppressed premiss ought to be, in order to support the conclusion.” Mr. Mill proceeds to illustrate this confusion by an excellent passage cited from Whately’s ‘Logic’. I may add, that Aristotle himself makes a remark substantially the same — That the same fallacy may be referred to one general head or to another, according to circumstances. Sophist. Elench. 33, 182, b. 10.
Value of formal debate as a means for testing and confuting fallacies.
We thus see not only that the fallacious agencies are self-operative, generating their own weeds in the common soil of human thought and speech, without being planted by Athenian Sophists or watered by Eristic — but that this very Eristic affords the best means of restraining their diffusion. It is only in formal debate that the disputant can be forced to make clear to himself and declare explicitly to others, without reserve or omission, all the premisses upon which his conclusion rests — that every part of these premisses becomes liable to immediate challenge by an opponent — that the question comes distinctly under consideration, what is or is not sufficient evidence — that the premisses of one argument can be compared with the premisses of another, so that if in the former you are tempted to acquiesce in them as sufficient because you have a bias favourable to the conclusion, in the latter you may be made to feel that they are insufficient, because the conclusion which they prove is one which you know to be untrue (reductio ad absurdum). The habit of formal debate (called by those who do not like it, Eristic[63]) is thus an indispensable condition both for the exposure and confutation of fallacies, which exist quite independent of that habit — owing their rise and prevalence to deep-seated psychological causes.
[63] The Platonic critics talk about the Eristics (as they do about the Sophists) as if that name designated a known and definite class of persons. This is altogether misleading. The term is vituperative, and was applied by different persons according to their own tastes.
Ueberweg remarks with great justice, that Isokrates called all speculators on philosophy by the name of Eristics. “Als ob jener Rhetor nicht (wie ja doch Spengel selbst gut nachgewiesen hat) alle und jede Spekulation mit dem Nahmen der Eristik bezeichnete.” (Untersuchungen über die Zeitfolge der Plat. Schriften, p. 257.) In reference to the distinction which Aristotle attempts to draw between Dialectic and Eristic — the former legitimate, the latter illegitimate — we must remark that even in the legitimate Dialectic the purpose prominent in his mind is that of victory over an opponent. He enjoins that you are not only to guard against your opponent, lest he should out-manœuvre you, but you are to conceal and disguise the sequence of your questions so as to out-manœuvre him. Χρὴ δ’ ὅπερ φυλάττεσθαι παραγγέλλομεν ἀποκρινομένους, αὐτοὺς ἐπιχειροῦντας πειρᾶσθαι λανθάνειν. Anal. Prior. ii. 66, a. 32. Compare Topic. 108, a. 25, 156, a. 23, 164, b. 35.
Without the habit of formal debate, Plato could not have composed his Euthydêmus, nor Aristotle the treatise De Sophisticis Elenchis.
Without the experience acquired by this habit of dialectic debate at Athens, Plato could not have composed his Euthydêmus, exhibiting a reductio ad absurdum of several verbal fallacies — nor could we have had the logical theories of Aristotle, embodied in the Analytica and Topica with its annexed treatise De Sophisticis Elenchis, in which various fallacies are discriminated and classified. These theories, and the corollaries connected with them, do infinite honour to the comprehensive intellect of Aristotle: but he could not have conceived them without previous study of the ratiocinative process. He, as the first theorizer, must have had before him abundant arguments explicitly laid out, and contested, or open to be contested, at every step by an opponent.[64] Towards such habit of formal argumentation, a strong repugnance was felt by many of the Athenian public, as there is among modern readers generally: but those who felt thus, had probably little interest in the speculations either of Plato or of Aristotle. That the Platonic critics should themselves feel this same repugnance, seems to me not consistent with their admiration for the great dialectician and logician of antiquity: nor can I at all subscribe to their view, when they present to us the inherent infirmities of the human intellect as factitious distempers generated by the habit of formal debate, and by the rapacity of Protagoras, Prodikus, and others.