Possible Duplicate:
“All but” idiom has two meanings?
It seems kind of counterintuitive, but saying that:
I'm all but convinced that ponies eat leprechauns.
means
I'm absolutely convinced that ponies eat leprechauns.
It seems that this is backwards; it would seem to mean "I'm everything except convinced that ponies eat leprechauns," meaning that I'm not convinced, but open to the possibility.
What does this "all but (adjective)" conjunction mean?