The Acquisition of Logical Words Stephen Crain, Andrea Gualmini and Luisa Meroni University of Maryland at College Park Introduction This study investigates children's interpretation of logical words. The main focus is children's understanding of the disjunction operator or, but we will also comment on children's understanding of the indefinite article, and the interaction between negation and logical connectives. A brief review of previous research on child language indicates the importance of different design features of the experimental techniques used to assess children's semantic competence. We compare two techniques, the act-out task and the truth value judgment task, and conclude that use of the act-out task has led to a misleading picture of children's semantic knowledge. We review the findings of our own recent studies using the truth value judgment task, the results of which are more in keeping with the expectations of current linguistic theory. The findings of these studies are then interpreted within the framework of a specific model of the language processing system, called the modularity matching model. Finally, we report the design and results of a new experiment designed to test a further prediction of the modularity matching model. 1 The Interpretation of Scalar Terms In current semantic research it is often assumed that language users assign to logical words a semantics which conforms to classical logic (see Chierchia and McConnell-Ginet, 1990). Assuming that Universal Grammar provides the truth conditions for logical operators, language learners are expected to know the truth conditions associated with logical operators as soon as they identify the words of the language that map onto them. For example, the disjunction operator corresponds to the word or in English. This operator is assumed to have truth conditions such that “S 1 or S 2 ” is true if either S 1 is true, or S 2 is true, or both S 1 and S 2 are true. Children are expected to judge sentences according to these truth conditions as soon as they figure out that the English word or maps onto the disjunction operator (presumably at Logical Form). In producing and understanding sentences containing logical words, however, language users are also influenced by pragmatic factors. The most basic principle