The eras of an intellectual discipline are delineated by sets of central questions, each yoked to preferred methods of inquiry. Some questions are answered, if only temporarily; many are discarded because they were improperly framed; most are reworded to accommodate to new information. Physicists know why eclipses occur, do not worry about the "aether," and attempt to determine the number of basic particles rather than define an atom.
Psychologists too, have answered, discarded, or rephrased questions during the short history of the discipline. We now have some insight into the nature of color vision, do not ask about the essence of will, and probe the conditions that monitor the performance of a coherent set of actions rather than seek the intrinsic meaning of reinforcement. Developmental psychologists, in a field with an even shorter history, have clarified some puzzles that provoked brooding among sixteenth century scholars. Infants apparently see hues as adults ( Bornstein, 1975) and are afraid of events they do not understand ( Kagan, 1976). We have stopped looking for the spirits that bewitch infants, and have begun to substitute statements about the developmental course of specific competences in task contexts for principles about intelligence.
One of the most vital changes in perspective regards the role of experience. We used to ask, "How does experience alter the child's behavior?" because we assumed that all experience had some effect on the young child. We now entertain the possibility that maturational constraints