Is the phrase “I’m afraid not,” such as in the below exchange, an idiom? It does not seem to make sense to me.
“May I please have the newspaper?” “I’m afraid not.”
Would that construction not indicate “I am not afraid?” To me, it seems that perhaps the phrase came from the shortening of “I’m afraid I can not” by dropping the “can” which completely ruins the ability of the phrase to make logical sense.
Even if I am correct in my assumptions, the phrase is still commonly used and understood. However, in formal writing, should I purposely avoid using this phrase due to my above concerns?