Note 62 — Chapter XXI · EUTHYDEMUS.

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.