This investigation studied the development of certain predicates called factives, such as "sad,""happy,""know," and "true," by studying the semantic effects of negation on the complements of both factive and non-factive predicates. The subjects were 60 children, divided into three age groups of ten boys and ten girls each; group one, ages 3 1/2 to 4 1/2; group two, ages 4 1/2 to 5 1/2; and group three, ages 6 to 8. The children's comprehension of factive and non-factive predicates was studied by having them choose one of two possible agents after hearing affirmative and negative factive and non-factive sentences. They could choose the agent mentioned in the complement, thus affirming the complement, or choose the unmentioned agent, thus denying the complement. Competence increased into the early school years; the oldest subjects showed a fair mastery of the factive predicates of the study and also showed both general and fine discrimination of the semantics of the non-factive predicates, particularly between the semantics of "true" and "posible" versus those of "think,""want," and "desire," The simplest factive, "know" was comprehended earliest of the studied factives. Affective factives such as "happy" and "nice" were acquired later. (MKM)