Recently I was helping a friend with a manuscript she was preparing and she had used the phrase "begs the question" -- but it didn't sound right, not in that context. She had used it in the sense of "demands that the question be asked" but I was pretty sure that wasn't what the phrase really means. Kinda like the judge who said, "I can't define porn but I know it when I see it."
Here's a fine example from an old Burns and Allen sketch.
Gracie: Gentlemen prefer blondes.
George: How do you know that?
Gracie: A gentleman told me.
George: How did you know he was a gentleman?
Gracie: Because he preferred blondes.
Alas, since looking it up, I've seen example after example in the press or on the internet of people using the phrase as my friend did. I have a real feeling that this incorrect usage is on its way to acceptance. Which isn't surprising as to beg the question certainly sounds like it means to ask for the question.
Our changing language . . .
Be on the lookout for circular reasoning if you find yourself at the Thanksgiving table and involved in one of those arguments that your irascible uncle or your holier-than-thou mother-in-law is likely to prompt.