For 90 college students, matched for SAT scores, there was differentiation of ability to identify correctly complex conjunctive concepts in a card-sorting task, as demonstrated by ability to learn the concepts to an errorless trial and to apply the newly formed concepts to other materials. Some Ss were able to learn the concepts to an errorless trial and to apply each concept to new sorts but were then unable to verbalize correctly those rules they had just employed. The same Ss who had previously learned an equivalent principle for sorting in one situation, then having tried unsuccessfully to verbalize the concept which they had just employed, were unable to apply the same principle in a new, equivalent situation.
