Human development from about ages 2 to 5 is presented in terms of the history of a child conceptualized in terms of stimulus and response functions and his interactions in current situations which consist of organismic, physical, and social conditions. The concepts describing the changes that occur during this developmental period, such as exploratory behavior, cognitive behavior, and moral behavior are invariably cast in nonobservable terms indigenous to the psychoanalytic, social learning, and cognitive approaches. To make them consistent with the objectives, assumptions, and principles of a functional analysis of behavior, these concepts must be reanalyzed and redefined. The resulting reformulations would have extensive implications for research and for practical applications. (Author/CS)