ave no argument _ad rem_, and none
either _ad hominem_, you can make one _ad auditores_; that is to say,
you can start some invalid objection, which, however, only an expert
sees to be invalid. Now your opponent is an expert, but those who form
your audience are not, and accordingly in their eyes he is defeated;
particularly if the objection which you make places him in any
ridiculous light. People are ready to laugh, and you have the laughers
on your side. To show that your objection is an idle one, would
require a long explanation on the part of your opponent, and a
reference to the principles of the branch of knowledge in question, or
to the elements of the matter which you are discussing; and people are
not disposed to listen to it.

For example, your opponent states that in the original formation of a
mountain-range the granite and other elements in its composition were,
by reason of their high temperature, in a fluid or molten state; that
the temperature must have amounted to some 480 deg. Fahrenheit; and that
when the mass took shape it was covered by the sea. You reply, by an
argument _ad auditores_, that at that temperature--nay, indeed, long
before it had been reached, namely, at 212 deg. Fahrenheit--the sea would
have been boiled away, and spread through the air in the form of
steam. At this the audience laughs. To refute the objection, your
opponent would have to show that the boiling-point depends not only on
the degree of warmth, but also on the atmospheric pressure; and that
as soon as about half the sea-water had gone off in the shape of
steam, this pressure would be so greatly increased that the rest of it
would fail to boil even at a temperature of 480 deg.. He is debarred from
giving this explanation, as it would require a treatise to demonstrate
the matter to those who had no acquaintance with physics.

XXIX.[1]

[Footnote 1: See sec. xviii.]

If you find that you are being worsted, you can make a
_diversion_--that is, you can suddenly begin to talk of something
else, as though it had a bearing on the matter in dispute, and
afforded an argument against your opponent. This may be done without
presumption if the diversion has, in fact, some general bearing on the
matter; but it is a piece of impudence if it has nothing to do with
the case, and is only brought in by way of attacking your opponent.

For example, I praised the system prevailing in China, where there is
no such thing as hereditary