“That’s all very well in theory, but it won’t do in practice.” In this sophism you admit the premisses but deny the conclusion, in contradiction with a well-known rule of logic. The assertion is based upon an impossibility: what is right in theory must work in practice; and if it does not, there is a mistake in the theory; something has been overlooked and not allowed for; and, consequently, what is wrong in practice is wrong in theory too.
When you state a question or an argument, and your opponent gives you no direct answer or reply, but evades it by a counter-question or an indirect answer, or some assertion which has no bearing on the matter, and, generally, tries to turn the subject, it is a sure sign that you have touched a weak spot, sometimes without knowing it. You have, as it were, reduced him to silence. You must, therefore, urge the point all the more, and not let your opponent evade it, even when you do not know where the weakness which you have hit upon really lies.
There is another trick which, as soon as it is practicable, makes all others unnecessary. Instead of working on your opponent’s intellect by argument, work on his will by motive; and he, and also the audience if they have similar interests, will at once be won over to your opinion, even though you got it out of a lunatic asylum; for, as a general rule, half an ounce of will is more effective than a hundredweight of insight and intelligence. This, it is true, can be done only under peculiar circumstances. If you succeed in making your opponent feel that his opinion, should it prove true, will be distinctly prejudicial to his interest, he will let it drop like a hot potato, and feel that it was very imprudent to take it up.
A clergyman, for instance, is defending some philosophical dogma; you make him sensible of the fact that it is in immediate contradiction with one of the fundamental doctrines of his Church, and he abandons it.
A landed proprietor maintains that the use of machinery in agricultural operations, as practised in England, is an excellent institution, since an engine does the work of many men. You give him to understand that it will not be very long before carriages are also worked by steam, and that the value of his large stud will be greatly depreciated; and you will see what he will say.
In such cases every man feels how thoughtless it is to sanction a law unjust to himself—quam temere in nosmet legem sancimus iniquam! Nor is it otherwise if the bystanders, but not your opponent, belong to the same sect, guild, industry, club, etc., as yourself. Let his thesis be never so true, as soon as you hint that it is prejudicial to the common interests of the said society, all the bystanders