namely, the conclusion which he
draws, that because his proposition is true, ours is false. In this
way his refutation is itself directly refuted by a denial of his
conclusion, _per negationem consequentiae_. Another trick is to refuse
to admit true premisses because of a foreseen conclusion. There are
two ways of defeating it, incorporated in the next two sections.

IV.

If you want to draw a conclusion, you must not let it be foreseen, but
you must get the premisses admitted one by one, unobserved, mingling
them here and there in your talk; otherwise, your opponent will
attempt all sorts of chicanery. Or, if it is doubtful whether your
opponent will admit them, you must advance the premisses of these
premisses; that is to say, you must draw up pro-syllogisms, and get
the premisses of several of them admitted in no definite order.
In this way you conceal your game until you have obtained all the
admissions that are necessary, and so reach your goal by making a
circuit. These rules are given by Aristotle in his _Topica_, bk.
viii., c. 1. It is a trick which needs no illustration.

V.

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 versa_. 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, maintaini