Most argument is a wandering from the subject, a confusion of the question, an increasing divergence from the point. Stick to the matter in hand.
When your adversary brings in subjects not relevant, do not attempt to answer them. Ignore them, lest you both go astray and drift into empty vituperation.
For instance, President Wilson, in the “Lusitania” incident, called Germany’s attention to the fact that her submarines had destroyed a merchant ship upon the high seas, the whole point being that this had been done without challenge or search and without giving non-combatant citizens of a neutral country a chance for their lives. Germany’s reply discussed points that had no bearing upon this issue, such as various acts of England. Mr. Wilson, in his reply, wisely refused to discuss these irrelevant things, an example of intelligent controversy.
Keep cool. The worse your case, the louder your voice.
Be courteous. Avoid epithets. Do not use language calculated to anger or offend your opponent. Such terms weaken the strength of your position.
A controversy is a conflict of reasons, not of passions. The more heat the less sense.
Keep down your ego. Do not boast. Do not emphasize what you think, what you believe, and what you feel; but try to put forth such statements as will induce your opponent to think, believe, and feel rationally.
Wait. Give your adversary all the time he wants to vent his views. Let him talk himself out. Wait your turn, and begin only when he is through.
Agree with him as far as you can. Give due weight, and a little more, to his opinions. It was the art of Socrates, the greatest of controversialists, to let a man run the length of his rope, that is, to talk until he had himself seen the absurdity of his contention.
Most men argue simply to air their convictions. Give them room. Often when they have fully exhausted their notions they will come gently back to where you want them. They are best convinced when they convince themselves.