First of all, we must consider the essential nature of every dispute:
what it is that really takes place in it.
Our opponent has stated a thesis, or we ourselves,--it is all one.
There are two modes of refuting it, and two courses that we may
pursue.
I. The modes are (1) _ad rem_, (2) _ad hominem_ or _ex concessis_.
That is to say: We may show either that the proposition is not in
accordance with the nature of things, i.e., with absolute, objective
truth; or that it is inconsistent with other statements or admissions
of our opponent, i.e., with truth as it appears to him. The latter
mode of arguing a question produces only a relative conviction, and
makes no difference whatever to the objective truth of the matter.
II. The two courses that we may pursue are (1) the direct, and (2) the
indirect refutation. The direct attacks the reason for the thesis; the
indirect, its results. The direct refutation shows that the thesis is
not true; the indirect, that it cannot be true.
The direct course admits of a twofold procedure. Either we may
show that the reasons for the statement are false (_nego majorem,
minorem_); or we may admit the reasons or premisses, but show that the
statement does not follow from them (_nego consequentiam)_; that is,
we attack the conclusion or form of the syllogism.
The direct refutation makes use either of the _diversion_ or of the
_instance_.
_(a)_ The _diversion_.--We accept our opponent's proposition as true,
and then show what follows from it when we bring it into connection
with some other proposition acknowledged to be true. We use the two
propositions as the premisses of a syllogism giving a conclusion which
is manifestly false, as contradicting either the nature of things,[1]
or other statements of our opponent himself; that is to say, the
conclusion is false either _ad rem_ or _ad hominem_.[2] Consequently,
our opponent's proposition must have been false; for, while true
premisses can give only a true conclusion, false premisses need not
always give a false one.
[Footnote 1: If it is in direct contradiction with a perfectly
undoubted, truth, we have reduced our opponent's position _ad
absurdum_.]
[Footnote 2: Socrates, in _Hippia Maj. et alias_.]
_(b) The instance_, or the example to the contrary.--This consists in
refuting the general proposition by direct reference to particular
cases which are included in it in the way in which it is stated, but
to which it does not apply, and by which it is therefore shown to be
necessarily false.
Such is the framework or skeleton of all forms of disputation; for to
this every kind of controversy may be ultimately reduced. The whole of
a controversy may, however, actually proceed in the manner described,
or only appear to do so; and it may be supported by genuine or
spurious arguments. It is just because it is not easy to make out
the truth in regard to this matter, that debates are so long and so
obstinate.
Nor can we, in ordering the argument, separate actual from apparent
truth, since even the disputants are not certain about it beforehand.
Therefore I shall describe the various tricks or stratagems without
regard to questions of objective truth or falsity; for that is a
matter on which we have no assurance, and which cannot be determined
previously. Moreover, in every disputation or argument on any subject
we must agree about something; and by this, as a principle, we must be
willing to judge the matter in question. We cannot argue with those
who deny principles: _Contra negantem principia non est disputandum_.