A usage-based view takes grammar to be the cognitive organization of one's experience with language. Aspects of that experience, for instance, the frequency of use of certain constructions or particular instances of constructions, have an impact on representation that is evidenced in speaker knowledge of conventionalized phrases and in language variation and change. It is shown that particular instances of constructions can acquire their own pragmatic, semantic, and phonological characteristics. In addition, it is argued that high-frequency instances of constructions undergo grammaticization processes (which produce further change), function as the central members of categories formed by constructions, and retain their old forms longer than lower-frequency instances under the pressure of newer formations. An exemplar model that accommodates both phonological and semantic representation is elaborated to describe the data considered.