To prove the truth of a proposition, you may also employ previous propositions that are not true, should your opponent refuse to admit the true ones, either because he fails to perceive their truth, or because he sees that the thesis immediately follows from them. In that case the plan is to take propositions which 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.[1] [Footnote 1: Aristotle, _Topica_ bk. viii., chap. 2.] VI. 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.[1] [Footnote 1: _Idem_, chap. 11. The last chapter of this work contains some good rules for the practice of Dialectics.] VII. Should the disputation be conducted on somewhat strict and formal lines, and there be a desire to arrive at a very clear understanding, he who states the proposition and wants to prove it may proceed against his opponent by question, in order to show the truth of the statement from his admissions. The erotematic, or Socratic, method was especially in use among the ancients; and this and some of the tricks following later on are akin to it.[1] [Footnote 1: They are all a free version of chap. 15 of Aristotle's _De Sophistici Elenchis_.] The plan is to ask a great many wide-reaching questions at once, so as to hide what you want to get admitted, and, on the other hand, quickly propound the argument resulting from the admissions; for those who are slow of understanding cannot follow accurately, and do not notice any mistakes or gaps there may be in the demonstration. VIII. This trick consists in making your opponent angry; for when he is angry he is incapable of judging aright, and perceiving where his advantage lies. You can make him angry by doing him repeated injustice, or practising some kind of chicanery, and being generally insolent. IX.