In this volume, the author reviews the results of research on language performance and proposes a model of production and comprehension. Although recent developments in linguistics are taken into account, consideration of other requirements of a performance model leads to the conclusion that the grammar the speaker has in mind differs from the grammar as currently conceived of by most linguists. The author is also critical of recent computer simulations of language performance on the basis that they fall short of describing what goes on in human production and comprehension. The author therefore proposes that the basic issues must be rethought and new theoretical foundations reformulated, in order to arrive at a viable theory of language functioning. In developing the framework of the model presented in this book, requirements of flexibility in the performance mechanisms, the probabilistic nature of comprehension processes, and the interleaving of linguistic rules with context and knowledge of the world are emphasized.