If you make an induction, and your opponent grants you the particular cases by which it is to be supported, you must refrain from asking him if he also admits the general truth which issues from the particulars, but introduce it afterwards as a settled and admitted fact; for, in the meanwhile, he will himself come to believe that he has admitted it, and the same impression will be received by the audience, because they will remember the many questions as to the particulars, and suppose that they must, of course, have attained their end.
If the conversation turns upon some general conception which has no particular name, but requires some figurative or metaphorical designation, you must begin by choosing a metaphor that is favourable to your proposition. For instance, the names used to denote the two political parties in Spain, Serviles and Liberates, are obviously chosen by the latter. The name Protestants is chosen by themselves, and also the name Evangelicals; but the Catholics call them heretics. Similarly, in regard to the names of things which admit of a more exact and definite meaning: for example, if your opponent proposes an alteration, you can call it an innovation, as this is an invidious word. If you yourself make the proposal, it will be the converse. In the first case, you can call the antagonistic principle “the existing order,” in the second, “antiquated prejudice.” What an impartial man with no further purpose to serve would call “public worship” or a “system of religion,” is described by an adherent as “piety,” “godliness”: and by an opponent as “bigotry,” “superstition.” This is, at bottom, a subtle petitio principii. What is sought to be proved is, first of all, inserted in the definition, whence it is then taken by mere analysis. What one man calls “placing in safe custody,” another calls “throwing into prison.” A speaker often betrays his purpose beforehand by the names which he gives to things. One man talks of “the clergy”; another, of “the priests.”
Of all the tricks of controversy, this is the most frequent, and it is used instinctively. You hear of “religious zeal,” or “fanaticism”; a “faux pas” a “piece of gallantry,” or “adultery”; an “equivocal,” or a “bawdy” story; “embarrassment,” or “bankruptcy”; “through influence and connection,” or by “bribery and nepotism”; “sincere gratitude,” or “good pay.”
To make your opponent accept a proposition, you must give him the counter-proposition as well, leaving him his choice of the two; and you must render the contrast as glaring as you can, so that to avoid being paradoxical he will accept the proposition, which is thus made to look quite probable. For instance, if you want to make him admit that a boy must do everything that his father tells him to do, ask him “whether in all things we must obey or disobey our parents.” Or, if a thing is said to occur “often,” ask whether by “often” you are to understand few or many cases; and he will say “many.” It is as though you were to put grey next black, and call it white; or next white, and call it black.