ABSTRACT
THE main difference between the operational classifications of stage III and the imaginal or graphic classifications found at stage I is that the child who is more mature is very much more flexible in the way he handles the elements. This applies both to his mental perspective and to the actual shuffling and reshuffling of which he is capable. He shows flexibility in hindsight when he can change the criterion, either because he notices some property which he failed to take into account when he started, or because the experimenter brings in additional elements to add to an existing classification. He shows flexibility in foresight when he can mentally anticipate a classification before putting it into practice, and particularly when he is able to choose the best classification out of a number of possible alternatives without overt trial-and-error.
