Extensive longitudinal data were gathered on a child's entry into the symbolically mediated modal world by examining changes in the semantics and pragmatics of her uses of modal auxiliary verbs. The data are 53 transcripts of natural conversations between a girl, Nina, and her mother recorded periodically from her 23rd month to her 39th month. The focus is on 1,826 modal expressions she produced. The three major analyses used were a semantic analysis, conversational act analysis to ask what she is doing when she uses a modal, and a third analysis to ascertain what worlds her modal utterances referred to. The modalities fall into three categories: (1) the dynamic, or logic of factual conditions for action; (2) the deontic, or the normative conditions; and (3) the epistemic, or logic of knowledge or belief claims. Nina's first modals were produced at age 2 years, 2 months. Her overall modal production increased in each of the 4-month periods, along with a steady increase in the number of different forms. The overall analysis shows that Nina used modals more frequently to initiate than to respond to turns of talk. By her use of modals, she formulates and communicates plans, structures and enriches the world of pretend play she creates, and coordinates and shares her meaningful actions with others. (AMH)