A mainstay of functional linguistics has been the claim that linguistic elements and patterns that are frequently used in discourse become conventionalized as grammar. This book addresses the two issues that are basic to this claim: first, the question of what types of elements are frequently used in discourse and second, the question of how frequency of use affects cognitive representations. Reporting on evidence from natural conversation, diachronic change, variability, child language acquisition and psycholinguistic experimentation the original articles in this book support two major principles. First, the content of people's interactions consists of a preponderance of subjective, evaluative statements, dominated by the use of pronouns, copulas and intransitive clauses. Second, the frequency with which certain items and strings of items are used has a profound influence on the way language is broken up into chunks in memory storage, the way such chunks are related to other stored material and the ease with which they are accessed to produce new utterances.