MODELS AND RULERS IN DYNAMICAL DEVELOPMENT

Non-linear dynamics holds enormous promise for transforming the field of development, moving it from rich but loose descriptions of developm ental processes toward powerfully explicated dynamical models of chang e that are closely linked to empirical data about growth functions. Th e study of cusp catastrophes in developmental transitions provides an example of the beginning of this transformation. For the dynamics revo lution to live up to its promise, researchers need not only to build o n the tools that are explained in this special issue but also to move beyond catastrophe models of transition to deal with a fuller range of developmental processes, including hierarchical-growth and predator-p rey models. If researchers are to ground these models effectively in o bservations, they must focus on building sound rulers of development t o replace the poorly constructed scales that are the norm in the study of cognitive development. The papers in this special issue point the way towards achieving important parts of this agenda.