Abstract
A human life-span model was derived from Piaget''s population-dynamic interpretation of the 2-tiered function of logic in adaptation: logical intercoordination and variation, and contextual-pragmatic selection. In this model specialization, concern with concrete pragmatics and pressures towards social system stability are all seen to be aspects of progressive, directional and structural change in adulthood. Suggestions bearing on interpretations of adult cognitive change are offered.