Even among individuals operating at Piaget's highest cognitive level (Formal Operations Stage) there is a range of behaviors on important cognitive characteristics. Various substages and their performance criteria are suggested. (JD)

Intended as a nontechnical review of current scientific knowledge in the field, this essay considers the nature of primary and secondary intellectual abilities, plus the major features of, and the development of individual differences in, the skills and capacities constituting intelligence. Part of a theme issue on intelligence. (Author/SJL)