XXVII.

Should your opponent surprise you by becoming particularly angry at an argument, you must urge it with all the more zeal; not only because it is a good thing to make him angry, but because it may be presumed that you have here put your finger on the weak side of his case, and that just here he is more open to attack than even for the moment you perceive.

XXVIII.

This is chiefly practicable in a dispute between scholars in the presence of the unlearned.  If you have 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.