Identity: key to children's understanding of belief.

Is knowledge structured and acquired as independent facts and concepts, as parcels of independent domains, or as domains that share conceptual abilities? For an answer, we looked at the development of two concepts, belief and identity. These concepts are not part of the same domain, but the application of both depends on the common ability to separate sense from reference. We show that both capacities become functional between the ages of 3 and 5 years, which provides empirical support for the contention that deep conceptual structures play an important role in cognitive development.