Words, Thoughts, and Theories articulates and defends the "theory theory" of cognitive and semantic development—the idea that infants and young children, like scientists, learn about the world by forming and revising theories, a view of the origins of knowledge and meaning that has broad implications for cognitive science. Gopnik and Meltzoff interweave philosophical arguments and empirical data from their own and other's research. Both the philosophy and the psychology, the arguments and the data, address the same fundamental epistemological question: How do we come to understand the world around us? Recently, the theory theory has led to much interesting research. However, this is the first book to look at the theory in extensive detail and to systematically contrast it with other theories. It is also the first to apply the theory to infancy and early childhood, to use the theory to provide a framework for understanding semantic development, and to demonstrate that language acquisition influences theory change in children.