Developmental transitions: So what's new?

Structural approaches to development, such as Piaget's stage theory, have proved to be problematic in dealing with developmental transitions. More promising in this respect are models of qualitative change that address macroscopical phase shifts in non-linear dynamicalsystems that arise from quantitative changes at the microscopical level. In this introductory paper, we attempt to clarify the meanings of some of the core terms used in these models so as to set the scene for the subsequent contributions. We stress the relevance of recent advances in catastrophe theory for detecting developmental transitions and suggest that the concept of self-organisation as formulated in irreversible thermodynamics provides a framework for explaining them. As yet, there is a lack of convincing evidence that transitions of interest to developmental psychologists comply with principles of self-organisation that have become well-established for time-evolving systems in other disciplines such as chemistry and biology. Demonstrations of self-organisation in psychologically-relevant simulation models are a first step in attaining such evidence. In this special issue, we concentrate primarily on a common approach to the detection of transitions across a number of domains of development.However, in doing so illustrations are given of the ways in which the hypothesis of selforganisation can be used to account for the mechanisms of developmental transitions.