 Infants are able to make generalizations concerning kinds and categories in their first year of life (e.g., Baldwin, Markman, and Melartin 1993), and by the mid-preschool years, children hold richly structured and detailed beliefs about the general properties of members of kinds (e.g., Gelman 2003). An important question in cognitive development concerns the nature of these generalizations. How might we characterize these cognitively fundamental generalizations? To what sorts of information is our most basic way of generalizing sensitive? And how might these generalizations be articulated in natural language, once it is acquired?