Circular Argument
Circular Argument or Arguing in a circle, also known as Begging the Question and Petitio Principii, is a very common fallacy, very easy to fall into.
The etymology of the phrase begging the question according to logician Dr Gary N. Curtis on his Fallacy Files web site, is interesting:
The phrase "begging the question", or "petitio principii" in Latin, refers to the "question" in a formal debate—that is, the issue being debated. In such a debate, one side may ask the other side to concede certain points in order to speed up the proceedings. To "beg" the question is to ask that the very point at issue be conceded, which is of course illegitimate.
His clear and detailed analysis of Circular Argument fallacies is here.
Confusion about the term "begging the question"
An annoying non-logical problem that confuses our thinking about Circular Arguments is that the term "beg the question", meaning use a circular argument (see its origin above) has come to be used in a completely different sense, meaning merely "raise the question", "suggest the question", "invite the question", "bring to mind the question". On the assumption that people who use beg the question this way don't understand its use as a logical term, we should probably avoid it completely, and talk instead about arguing in a circle.
