Children face a major problem of induction in trying to learn the conventional object categories encoded by their language. From a severely limited amount of information about how a category term is used, the child must determine what the word refers to and how it relates to other terms in the child's lexicon. Part of the solution to this problem is that children can effectively focus on the correct meaning because they consider only some kinds of hypotheses. The goal of this project is to explore some of the ways in which children limit these hypotheses. The investigation will be organized around the following four topics. 1. When someone points to an object and labels it, how does the child determine that the term refers to the object category as opposed to all of the other possible things it could mean? The answer may be that children first assume that a new world will refer to a category of objects. The proposed studies examine the origins and boundary conditions of this assumption. Some of the studies will use preferential looking techniques with prelinguistic infants to determine what role hearing a word plays in guiding their attention to objects. 2. Another way children may constrain the meaning of terms is to assume that they are mutually exclusive. Children will be taught new terms that either adhere to or violate mutual exclusivity to determine how this constraint develops and how children use it to figure out the meaning of novel words. 3. Children may also narrow down a word's meaning by relying on the linguistic context in which the word is used. In some cases, this can be accomplished in a single exposure. The proposed studies examine how children use linguistic contrast to figure out the meanings of words across various semantic domains. 4. The final set of studies examines what children do when the context provides insufficient information about what a word means. How certain does a child have to be about the meaning of a word to set up a lexical entry? Whether children are conservative or use an error prone strategy will have strong implications for what the language mechanism is like. Together these studies will help explain the extraordinary ability children have to acquire new terms.