To mportillo14; Daniel Risberg; JohnD: Good question and good discussion!
Increasingly, in popular usage, the phrase ‘…such and such begs the question’ is used in discourse with the sense of ‘that gives rise to another question’ or ‘that presupposes another proposition’. I note somewhere in the lessons that it is probably useless to attempt to swim against the tide of popular usage at this stage and to insist on the logical meaning of the phrase.
As Daniel has neatly pointed out, the logical fallacy of BTQ is essentially that of assuming in a proof the very thing you are trying to prove. It’s rarely as obvious as, say, ‘Moral relativism is an untenable position because moral relativism is an untenable position”; more often, what is presented as evidence for a given conclusion is merely a verbal reformulation of the very conclusion one is aiming to establish. as, e.g. ‘Moral relativism is an untenable position because one cannot hold moral positions that are relative.’
Of course, such an argument form is formally valid! Quite clearly, if P is true, then P is true! The fallacy is informal because, of course, we want P to be derived from something other than just P.
Sometimes, BTQ is used to describe a form of circular argumentation, as in some of the examples Daniel provides in his second post.
I’m not at all confident that this is a ‘more structured and thorough answer’ that Daniel was certain I would provide but I think the material covered in the posts effectively gives the essence of the fallacy.
As I mention in the lessons, the material on the fallacies, though it has been around in one form or another since the time of Aristotle, has never achieved a universally definitive formulation. While there are many books and articles on the subject, some popular, some technical, the lists of fallacies, the precise definition of the fallacies, the typology of the fallacies – all these are theoretically contested matters. The good news, however, is that an acquaintance with those fallacies on which there is more or less a consensus will stand one in good stead in practical argumentation even if borderlines remain disputed and theory contested.