Page:The art of controversy and other posthumous papers (IA artofcontroversy00schouoft).pdf/34

 are false in themselves but true for your opponent, and argue from the way in which he thinks, that is to say, ex concessis. For a true conclusion may follow from false premisses, but not vice versâ. In the same fashion your opponent's false propositions may be refuted by other false propositions, which he, however, takes to be true; for it is with him that you have to do, and you must use the thoughts that he uses. For instance, if he is a member of some sect to which you do not belong, you may employ the declared opinions of this sect against him, as principles.

Another plan is to beg the question in disguise by postulating what has to be proved, either (1) under another name; for instance, "good repute" instead of "honour"; "virtue" instead of "virginity," etc.; or by using such convertible terms as "red-blooded animals" and "vertebrates"; or (2) by making a general assumption covering the particular point in dispute; for instance, maintaining the uncertainty of medicine by postulating the uncertainty of all human knowledge. (3) If, vice versâ, two things follow one from the other, and one is to be proved, you may postulate the other. (4) If a general proposition is to be proved, you may get your opponent to admit every one of the particulars. This is the converse of the second.