Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
afraid (adj.)
combines with of, as in We were afraid of causing more trouble, with for, as in I was afraid for my life, or with to plus an infinitive, as in She was afraid to ask. It is Standard in all. Afraid is almost always a predicate adjective. Even when no symptoms of fear are involved, afraid is perfectly proper in “regrettable, unfortunate” circumstances, as in I’m afraid I must disappoint you, even as it continues to involve real fear in other uses: In the dark and creaky house that night, he was afraid.
