Familiarity with the valid forms of logical reasoning and with the errors to which they are subject are prerequisites to success. It is not sufficient that the student have a vague feeling that there is something wrong with an argument; he must be able to locate the defect exactly and to point it out to others in such a way that they will see it. Vagueness and ambiguity are the very substance of fallacies. Sometimes the student must use his knowledge of constructive logic to build up a parallel argument in the way it ought to stand and show more plainly by means of contrast the defects of the unsound argument. In such cases it often happens that the evidence points in an opposite direction from that which is needed to support a valid argument. All of these devices should be utilized in making plain the existence of fallacies.
II. Reductio ad absurdum.
This method of refutation adopts for the time being the argument of an opponent and then by carrying out that argument to its logical conclusion shows that it is absurd. For example, Beecher answered those who favored the South, during the late Civil War, because they were “the weaker party,” by reducing their argument to an absurdity. He said,
“Nothing could be more generous than your doctrine that you stand for the ‘weaker’ party in a controversy, when that weak party stands for its own legitimate rights against imperious pride and power. But who ever sympathized with a weak thief, because three constables had got hold of him? And yet the one thief in three policemen’s hands is the weaker party. I suppose you would sympathize with him.”
The following quotation from Laycock and Scales’ Argumentation and Debate still further illustrates this method of refutation.
“This method is effective because of its simplicity and directness. It also has in it an element of ridicule that is persuasive against an opponent. William Ellery Channing, in a reply to Henry Clay on the slavery question, used this method as follows:—
“‘But this property, we are told, is not to be questioned on account of its long duration. “Two hundred years have sanctioned and sanctified negro slaves as property.” Nothing but respect for the speaker could repress criticism on this unhappy phraseology. We will trust it escaped him without thought. But to confine ourselves to the argument from duration; how obvious the reply! Is injustice changed into justice by the practice of ages? Is my victim made a righteous prey because I have bowed him to the earth till he cannot rise? For more than two hundred years heretics were burned, and not by mobs, not by lynch law, but by the decrees of councils, at the instigation of theologians, and with the sanction of the laws and religions of nations; and was this a reason for keeping up the fires, that they had burned two hundred years? In the eastern world, successive despots, not for two hundred years, but for twice two thousand, have claimed the right of life and death over millions, and with no law but their own will, have beheaded, bowstrung, starved, tortured unhappy men without number who have incurred their wrath; and does the lapse of so many centuries sanctify murder and ferocious power?’
“Again:—‘But the great argument remains. It is said that this property must not be questioned, because it is established by law. “That is property which the law declares to be property.” Thus human law is made supreme, decisive, in a question of morals. Thus the idea of an eternal, immutable justice is set at naught. Thus the great rule of human life is made to be the ordinance of interested men. But there is a higher tribunal, a throne of equal justice, immovable by the conspiracy of all human legislatures. “That is property which the law declares to be property.” Then the laws have only to declare you, or me, or Mr. Clay, to be property, and we become chattels and are bound to bear the yoke! Does not even man’s moral nature repel this doctrine too intuitively to leave time or need for argument?’”
III. The dilemma.
The dilemma is one of the most conclusive forms of refutation. It consists in forcing upon an opponent a choice between two possible solutions to the question under discussion, and then showing that both conclusions are unsound. These two conclusions are called the “horns of the dilemma.” It matters not which of the “horns” an opponent selects; the result is disastrous. For example, Lincoln used the dilemma against those who charged that the Republicans stirred up insurrection among the slaves and pointed to John Brown and his men as a specific example showing the truth of that charge. Lincoln said, “John Brown was no Republican; and you have failed to implicate a single Republican in his Harper’s Ferry enterprise. If any member of our party is guilty in that matter, you know it or you do not know it. If you do know it, you are inexcusable for not designating the man and proving the fact. If you do not know it, you are inexcusable for asserting it, and especially for persisting in the assertion after you have tried and failed to make the proof. You need not be told that persisting in a charge which one does not know to be true, is simply malicious slander.” In effect Lincoln said, “You know it or you do not know it. If you know it you are inexcusable. If you do not know it you are inexcusable. Whichever horn of the dilemma you accept, your conduct is inexcusable.”