Project Summary (Concepts and theories in human development) This proposal launches two new directions in the study of essentialist reasoning in children. Essentialism is the idea that certain categories have an underlying reality that determines identity and is responsible for commonalities among category members. Essentialism is argued to be an early cognitive bias (Gelman, 2003). Young children's concepts reflect a deep commitment to essentialism, which leads children to look beyond the obvious in many converging ways: when learning words, generalizing knowledge to new category members, contemplating the role of nature versus nurture, and constructing causal explanations. This framework thus argues against the standard view of children as concrete or focused on the obvious, instead claiming that children have an early, powerful tendency to search for non-obvious features. Essentialism also runs counter to claims that children build up their knowledge of the world wholly based on associative learning strategies, arguing instead that children's concepts are embedded in rich folk theories. This competing renewal builds on past work to address two aims. Part 1 examines how language serves as a mechanism for constructing and transmitting essentialist beliefs in preschool-aged children. Generic noun phrases (e.g., Bats fly at night) are a vital means of conveying essentialist concepts in natural language: they are frequent in parental input across widely distinct languages, are readily learned by young children, are understood appropriately by young children, and are retained in long-term memory. An in-depth training study is proposed that will teach young children a new concept under varied wording conditions, to chart the effects of generics and labeling on essentialist reasoning. This section will also examine the implications of different input language for children's memory for and learning of new information. Finally, studies in this section will test competing claims regarding the process by which generics are learned, and the mechanisms by which language affects categorization and similarity judgments. Part 2 examines one key hypothesized developmental underpinning of essentialism: attention to the historical path of objects, as manifest in concepts of origins, ownership, and authenticity. A series of studies is proposed to investigate the development of these core concepts in children from toddler age through elementary school. The theory predicts that preschool children will display keen sensitivity to historical path, and that such judgments will hold even when controlling for material features of objects, and when item desirability is placed in conflict with historical path. Furthermore, young children are predicted to judge that origins and ownership transmit special value to objects, although the scope of this belief is also predicted to broaden with age. Altogether, these 19 studies will provide converging and precise evidence regarding the links among concepts, language, and theory construction in early childhood, using naturalistic language analyses and experimental studies with children 2 to 10 years of age.