In undertaking a comprehensive scientific study of religion, as in the comprehensive study of any area of life, it is essential to include a developmental perspective. We cannot really comprehend an individual's present beliefs without knowing the past that has brought them into being. The study of religious cognition therefore demands a consideration of cognitive development. And no figure has had more influence on the study of cognitive development than Jean Piaget (1896—1980), the founder of constructivism, author or editor of over eighty books and over 500 articles and reports, and by his own admission, “the most criticized author in the history of psychology” (quoted by Smith 1996: vi). Despite his enormous contributions to child psychology, Piaget was not primarily interested in children for their own sake, but rather in what the study of children's minds could reveal about how adult cognition comes into being. He commented that “after having tried to describe the child's mentality as distinct from the adult's we have found ourselves obliged to include it in our descriptions of the adult mind in so far as the adult still remains a child” (Piaget 1932: 77). In Piaget's view, similar cognitive processes are found in both adults and children; yet qualitative differences in cognition arise because certain processes predominate in adults and others in children.