ABSTRACT
This chapter focuses on developmental research by emphasizing transitions and changes in addition to continuities and stabilities. It attempts to present a modest conceptualization of some of the major transitions in the mental development of infants in the first three years of life and to relate those transitions to changes in a variety of mental and social/emotional events typical of this period. The chapter presents two general conceptual orientations. One concerns the different ways in which developmental transitions may be manifest, and the second represents a developmental orientation toward the nature-nurture issue. A developmental function is continuous when changes over age are quantitative rather than qualitative, that is, when the fundamental nature of the attribute does not change. The most direct evaluation of a stage theory requires the creation of a pool of behavioral items that directly assess the hypothesized fundamental characteristic of each stage as well as behaviors encompassed by proposed horizontal decalages.
