Being vicious, circularly

We all beg for things from time to time, don't we? Remember the purple bike with the banana seat you wanted so badly when you were eight? And surely we ask questions of all sorts -- like "Why do cats purr?" and "When will the Martians return?" -- in contexts appropriate and inappropriate, maddening and marveling. So in what contexts is it appropriate to say that one "begs the question?"

Let's settle this once and for all. Begging the question entails committing an informal fallacy in which the speaker assumes in her premises just the thing that she is attempting to prove. Clever, and often useful at cocktail parties, begging the questions is a rhetorical spinning jenny, where the argument's thread goes round and round in a vicious circle.

What begging the question is not: a situation in which a certain question, like "Hey, isn't that Ingrid?", just NEEDS to be asked.

Miss Dickinson knew the difference between begging the question and having a question that was begging to be asked. Thus the Dickinsonian oracle recommends:

Lest this be Heaven indeed
An Obstacle is given
That always guages a Degree
Between Oursevles and Heaven.
(E. Dickinson, 1000)