"Keep to the point" is excellent advice in any kind of speaking or writing; and nowhere is it more desirable than in argument. But many people find it desperately difficult, especially, as is only natural, when they are not clear in their mind as to what the exact point is.
Consider the course of the following discussion
A: No patriot would refuse to take up arms in defence of his country.
B: Oh, come! What about the Quakers? They are forbidden by their religion to fight.
A: Yes, but they performed useful services in the last war—they acted as stretcher-bearers and hospital orderlies. It all comes to the same thing, doesn't it?
"A" is shifting his ground or ignoring the point. As it turns out, his original proposition does not mean what it says; it means something else that was at the back of "A"'s mind; it means, in effect, "No patriot would refuse to do what I consider a patriot ought to do." And that is not a very fruitful subject for discussion, is it?
"A"'s evasion of the point was no doubt unintentional and due more to haziness and carelessness than to deliberate intention to mislead. But it is a device commonly practised deliberately by those who have a weak case. If a barrister, acting for the prosecution in a criminal case, instead of proving that the accused had committed an atrocious fraud, concentrated his efforts on proving that the fraud of which he was accused was atrocious, he is deliberately throwing the jury "off the scent" by "dragging a red-herring across the trail."
Macaulay somewhere vehemently accuses the apologists of Charles I of blatantly ignoring the point: for, he says, when that ill-fated king's statesmanship is called in question, they harp on his piety, his faithfulness as a husband, his paternal solicitude for his children, etc. "Ample apologies indeed for fifteen years of persecution, tyranny and falsehood " —thus Macaulay clinches his argument.
Writers on logic have special names for the various kinds of ignoring the point. I will give you them because they are easy to understand and convenient to use for purposes of classification. They are all opposed to argumentum ad rem (i e. , to the point).
Argumentum ad hominem, i.e., an argument directed towards an individual. I overheard the following remark in the train the other day: "You shouldn't have any use for these new tariffs, for your bread and butter depends on the import trade." The speaker is trying to dissuade his opponent from the view the latter had expressed, by suggesting that his own livelihood would be adversely affected if it was adopted. But the argumentum ad hominem may be legitimately applied to individual people when we are taxing them with inconsistency. If, for example, someone has repeatedly asserted that the State system of education is the best and that the State primary schools provide by far the most satisfactory and efficient form of elementary education, and that it is everyone's duty to support them, and sends his own children to private preparatory schools, we should be justified, in the absence of any special circumstances affecting the case, in retorting, "Why, then, don't you send your children to the State primary schools?" But this type of argument, even when properly applied, is addressed to the peculiar circumstances, character, avowed opinions or past conduct of the individual, and therefore has a reference to him only, and does not bear directly and absolutely on the real question, and is thus not an argumentum ad rem.
Argumentum ad baculum (baculus = the "big stick"). This, strictly speaking, is not argument at all, but an appeal to force.
Argumentum ad populum is an appeal to popular passion or prejudice. "It's not done among the best people." "It's not cricket." "It's not British." The use of words or phrases with an emotional appeal, calculated to arouse passion or prejudice in the minds of their hearers, is a common rhetorical device to cloud the issue or to divert attention from the real point.
Argumentum ad ignorantiam is attempting to prove an affirmative by showing that the negative has never been established. "Mermaids must exist, because no one has ever proved that they don't." "Nobody has a good word to say for him; therefore he must be a scoundrel."
Argumentum ad verecundiam is appealing to reverence for some respected authority, or some venerable institution, or some long-cherished tradition, or one's own qualifications to speak with the voice of authority. Watch the correspondence column in your newspaper for expressions like these: "Speaking as a schoolmaster of some 35 years' experience..."
"Having spent the better part of a lifetime in the service of the British Raj in India. . . ." Observe also the attempts made to disguise an appeal ad verecundiam by the use of mock-modest introductory phrases; e.g., "I happen to be a licensed lay-reader. Naked appeals to authority usually arise from prejudice.
Perhaps the commonest form of ignoratio elenchi or ignoring the point is summed up in the legal tag, "No case: abuse plaintiff's attorney." This should explain itself.
These arguments are all irrelevant, but they are not dishonest, unless the man who uses them deliberately intends to deceive.