ABSTRACT
IN chs. I-IV we found that the difficulty of operational classification is largely due to the fact that young children cannot co-ordinate extension and intension. This sort of co-ordination is foreign to perception; nor does it play any part in sensori-motor organization. As a result we find a considerable time-lag between graphic collections, which are dominated by perceptual and sensori-motor configurations, and hierarchical classifications, which rely on the relation of class-inclusion. Multiplicative classification (as in matrices or multiple-entry tables) is somewhat nearer on the surface to the corresponding perceptual organization, since the logical interference of two or more properties is closely mirrored by an intuitive, symmetrical arrangement of objects. Nevertheless, we found that the operational organization is not a continuous development out of the perceptual organization, but that it relies on its own structurization—without which the correct solution of matrix problems tends to be misleading. Let us now see whether the development of seriation shows any parallel to what we have found in classification.
