Responds to Maccoby's and Hinde's commentaries on the Belsky, et al. article in this issue. Highlights several points of concurrence and disagreement. Draws attention to the potential benefits of asking questions about proximal and ultimate causation simultaneously and, thus, the need for child developmentalists to think about both the how and why…

Specifies some problems in the Piagetian characterizations of assimilation and accommodation and offers an alternative formulation intended to resolve some conceptual anomalies. On the basis of the revision, the orthogenetic law of developmental progression is explicitly derived. Further, Piaget's notion of "equilibrium" is extended into…