Development of formal hypothesis-testing ability.

The ability to test hypotheses, which has been postulated to play a central role in a va-riety of cognitive processes (e. g., Inhelder & Piaget, 1958; Neimark & Santa, 1975; Wason & Johnson-Laird, 1972), is one of those very general aspects of cognition that can be studied in some form at any level of development. At the level of formal operations, one might expect the development of relatively conscious hy-pothesis testing based on conceptualization of hypotheses as such. Both Piagetian theory and available evidence (see below) suggest the in-volvement of at least three cognitive capacities: (a) comprehension of implication relationships (if p then q; all p are q; or any logically isomor-