Circulus in demonstrando (circular argument). Circular argumentation occurs when someone uses what they are trying to prove as part of the proof of that thing. Here is one of my favorite examples (in pared down form): "Marijuana is illegal in every state in the nation. And we all know that you shouldn't violate the law. Since smoking pot is illegal, you shouldn't smoke pot. And since you shouldn't smoke pot, it is the duty of the government to stop people from smoking it, which is why marijuana is illegal!"

Circular arguments appear a lot in debate, but they are not always so easy to spot as the example above. They are always illegitimate, though, and pointing them out in a debate round looks really good if you can do it. The best strategy for pointing out a circular argument is to make sure you can state clearly the proposition being proven, and then pinpoint where that proposition appears in the proof. A good summing up statement is, "In other words, they are trying to tell us that X is true because X is true! But they have yet to tell us why it's true."


TMT