A model for the analysis of simple human conceptual behavior, based on the apparent similarities of human conceptual behavior and that of infrahuman subjects, is developed. A minimum definition of conceptual behavior is given: A single response, verbal or nonverbal, under the discriminative control of a group of stimuli whose parameters are defined by the differential reinforcement of the environment. In addition to the role of differential reinforcement in the development of stimulus control, other variables which are very important for the form of that control are procedures effecting stimulus presentation or stimulus programming. It is likely that programming procedures play increasingly important roles in the development of conceptual behavior as that behavior becomes more complex. One important set of behaviors which appears to fall into successive levels of complexity is mathematics; an analysis of the behavior of counting is given. The model developed consists basically of two assumptions about concept formation: (1) concepts are discriminated operants, with the major controlling variable being differential reinforcement; and (2) learning set procedures teach an organism to discriminate and quickly respond to differential consequences, and the same lesson may be learned at a slower rate while acquiring a large group of concepts in childhood. (DB)