Kenneth G. Wilson (1923–). The Columbia Guide to Standard American English. 1993.
incredible, incredulous (adjs.)
Incredible means “unbelievable”: The news you brought is incredible. Incredulous applies to people and their attitudes and means “unable or unwilling to believe”: She was incredulous, and she found his story incredible. The claim he made was outrageous, and the expressions on their faces were uniformly incredulous. Using incredulous to mean “unbelievable” was Standard until about two hundred years ago, but not today, except humorously as a malapropism. See CREDENCE.
