Piaget Jean (1896–1980), Swiss psychologist and epistemologist who profoundly influenced questions, theories, and methods in the study of cognitive development. The philosophical interpretation and implications of his work, however, remain controversial. Piaget regarded himself as engaged in genetic epistemology, the study of what knowledge is through an empirical investigation of how our epistemic relations to objects are improved. Piaget hypothesized that our epistemic relations are constructed through the progressive organization of increasingly complex behavioral interactions with physical objects. The cognitive system of the adult is neither learned, in the Skinnerian sense, nor genetically preprogrammed. Rather, it results from the organization of specific interactions whose character is shaped both by the features of the objects interacted with (a process called accommodation) and by the current cognitive system of the child (a process called assimilation). The tendency toward equilibrium results in a change in the nature of the interaction as well as in the cognitive system. Of particular importance for the field of cognitive development were Piaget’s detailed descriptions and categorizations of changes in the organization of the cognitive system from birth through adolescence. That work focused on changes in the child’s understanding of such things as space, time, cause, number, length, weight, and morality. Among his major works are The Child’s Conception of Number (1941), Biology and Knowledge (1967), Genetic Epistemology (1970), and Psychology and Epistemology (1970). See also EPISTEMOLOG. R.A.Sa.