Researchers in the field of language acquisition may adopt various particular theoretical approaches to the description and explanation of linguistic phenomena. They need this theory to describe the nature of what is or is not undergoing change over time. However linguistic theory normally makes no reference to the time dimension, a dimension crucial to any study of development. Psycholinguists, on the other hand, focus on temporal phenomena but these are normally measured in milliseconds. At the same time, they still need a coherent model of linguistic structure to carry out their investigations. The logic of this suggests that a framework is needed that integrates linguistic theories about the properties of language, i.e., linguistic knowledge, with theories about on-line processing. The need to integrate these two ways of looking at language is also crucial for researchers who study linguistic development in the individual. One such approach is Modular Growth and Use of Language (MOGUL), a theoretical framework based on a close examination of research in several disciplines and within which utterance processing plays a vital role in explaining development. In fact, in that part of MOGUL which is devoted to explaining acquisition, the claim is that development is a side-effect of making sense of language to which we are exposed. No special learning mechanisms are involved.