Harris presents a detailed overview of his own work in psychology (along with a survey of related literature), that explore the ways in which imagination and an understanding of causality and the mental states of others advance in children from about 24 to 60 months. Harris takes a position against Freud and Piaget, who felt that imagination was opposed to realism, and that an excess of imagination was a sign of a failure to understand and adapt to the real world, to demonstrate that even very young children can partake in fictive stances while understanding that they are fictional. Furthermore, several scales of imagination at different age groups appear to be strongly correlated with each other, along with linguistic development and social skills.

Harris provides a useful corrective to older theories in developmental psychology, but while I agree with his premise that imagination is a fundamental human capacity, I'm not sure that the evidence is strong enough to make his conclusions necessary.