The project will continue research on human concepts and their representation in the mind. The two main questions of interest are 1. how world knowledge and stimulus structure interact when people learn concepts, and 2. how concepts are involved in word meaning and language understanding. One group of studies investigates conceptual combination--how people combine two concepts to form a new, more complex concept. This work is important because it bears on the representation of individual concepts and on issues of language understanding. A theory of conceptual combination should explain how people use their concepts of bicycle and chain to understand a phrase like "bicycle chain." Thus, this work is closely connected to research on language comprehension. The proposed experiments investigate the construction of these concepts within sentences. One set of studies examines how emergent features are constructed, features that are true of the complex concept but not of its components (e.g., peeled apples are white, even though apples aren't normally white). Other experiments examine how sentence and discourse focus influences the construction process. Still other experiments study conceptual combination through the memory structures that such concepts create. A second group of studies involves adjective representation--how adjectives are represented in the mental lexicon. Theories of the lexicon have claimed that adjectives are organized by synonymy and antonymy, and the experiments will investigate the nature of these two relations. In particular, the experiments will discover how antonyms of adjectives vary depending on the nouns that they modify. This work has implications for explaining how people comprehend noun phrases. The third group os studies involves concept learning. Here, subjects are given examples of two categories and are asked to learn to tell the categories apart. The experiments investigate how knowledge of the domain helps to structure this task. In one experiment, different kinds of knowledge of the categories are compared to see how each component influences learning. In another experiment, different category structures are compared to discover how subjects learn each one. This research investigates one of the most basic of all our though processes--how we form classes of objects and then manipulate those classes during thinking and language understanding. This is a central topic in our understanding of the mind, and it is equally important in our understanding of cognitive disturbances in mental illness and brain damage. This work will also help us better understand word learning and the development of categorization in children.