I Beg to Differ

For Giggles:

Begging the Question (petitio principii, or "assuming the initial point") is a logical fallacy characterized by the initial proposition to be proved is assumed in the logic.  The initial proposition is never proved by the progression of the logic.  The word beg, unlike in the title of this post, has nothing whatsoever to do with asking for something.  Instead, it means to dodge, or avoid.

The Latin version, petitio principii, can literally be translated as "a request for the beginning or premise."  In other words, the premise (or argument) depends on the truth of the very matter in question.

Examples:

• Opium induces sleep because it has a soporific quality.
• To allow every man an unbounded freedom of speech must always be, on the whole advantageous to the State, for it is highly conducive to the interests of the community that each individual should enjoy a liberty perfectly unlimited of expressing his sentiments.

Or, more simply:

Person 1:  He is annoyed right now.

Person 2:  How can you tell?

Person 1:  Because he is really angry.

As Giggles pointed out in a comment on a previous post, "It's definitely not the same as 'raising a question.'"  However, it's being used more and more often as a synonym of raising a question and whether or not this common usage should be considered correct or incorrect is a question for experts in linguistic description and prescription of a living language.

(Most of this post was shamelessly plagiarized, albeit with slight alterations, from Wikipedia.)