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.] [Side-note: 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.