Introduction
The Circular Argument or "Begging the Question" fallacy, as it is sometimes known, is probably one of the most common fallacies employed in argument. Some are easy to pick out; other not so easy. This fallacy seeks to win an argument based on a premise that is based on the actual question at hand. The scholastic philosophers of the Middle Ages some times ran into this problem as they developed a formal style of debate. The whole point of argument is to convice someone that a proposition is true by appealing to facts and reasons that the other side concedes are true. There is no benefit to anyone to ask the other side to grant the very question at hand. A variant form of this fallacy is sometimes known as a complex question, which seeks to trap an opponent into accepting a proposition by proposing a question that presupposes the proposition. The classic example of this kind of fallacy is the "have you stopped beating your wife?" line.
Definition
The fallacy which attempts to defend a proposition by using the proposition itself as a premise in the argument.
Illustration
Jack: "No true Christian venerates relics. It's nothing less than idol worship!
Jill: "What about Catholics and the Orthodox?"
Jack: "But they are not genuine Christians."
Jill: "Why not?"
Jack: "Because they venerate relics."
Diagnosis
Circular Arguments are the most common form of fallacy, but they are not always the easiest thing to pick out. More complicated forms of this fallacy occur in multiple layers where sometimes the proposition in question is camoflaged with a little bit of dressing. Your opponent might start off with a number of premises which all seem to point to the conclusion, but one of those premises is closely related to the conclusion you are trying to deny. Other times it is very important to weed out the premises which presuppose the conclusion in order for them to have any weight. For instance, if I am arguing with an atheist about the existence of God, I cannot use the bible as "God's Word" to convince him since the bible assumes God's existence.
Antidote
The most effective way of exposing this argument is to carefully examine each premise your opponent is using, and ensure that he is not leveraging himself with a premise which relies on his conclusion for support. Many fallacious arguments can be shown to have this "look."
John Pacheco
The Catholic Legate
February 23, 2003