  Piaget generally ignored Behaviorism, and conducted experimental studies on the child’s evolving conception of the world. His extensive research agenda included the child’s understanding of space, time, God, objects, causality, morality, dreams, number, being alive, and more. Piaget’s specific questions and experimental results—which were reciprocally (mostly) ignored by Behaviorists—have served as a jumping off point for many Nativist-oriented theorists. But Piaget was not a Nativist. The heart of the Piagetian paradigm is his stage theory. On this view, children start with a very different conception of the world than adults have—in fact, Piaget thought that they start without a conception of an external world at all—and they go through a series of identifiable stages that culminate in adult understanding. The powerful unifying idea here is that there is something about the general character of these stages that is the same across all domains of understanding, and that the dynamics of stage transition is also uniform. To a first approximation, for Piagetians there are no significant distinctions between the developmental patterns in different domains of understanding. If we consider any domain, the stage theory imposes a uniform grid of steps in the development of that domain knowledge. The dynamic picture, again very roughly, is that a child at a stage proceeds until she faces an insurmountable obstacle; her present grasp of things makes it impossible for her to deal with a recalcitrant problem. This disequilibrium propels her to the next (pre-plotted) stage, in which new internal resources become available—an enriched conception of the world or a new flexibility in physical interaction—and the earlier problem can be resolved. The child recovers equilibrium until coping with problems again causes a crisis that leads to the availability of more new resources, and so on. The articulation of the Piagetian paradigm involved understanding the general nature of these stage-transitions better, exploring how the stage theory operates in specific domains, and understanding the new cognitive and behavioral resources that make these transitions possible.