operative in the process of grammaticalization or the creation of new grammar (see also Boyland 1997 for a discussion of the psychological mechanisms involved).Some comparable research in the phonological domain has begun to appear in recent years. For instance, several studies have shown that speakers judgments of the grammaticality of phonotactic patterns is based on the frequency of consonant and vowel combinations actually occurring in the language (Pierrehumbert 1994, Frisch 1996). In addition, speakers ability to access the lexicon may involve a complex interplay between the frequency of words and the number and frequency of words with similar phonological shape (Pisoni et al. 1985). Connectionism offers the possibility of formally modeling the effect of use on mental representations of language, and such models have been tested in the phonological and morphological domains (for example in Dell 1989 and Daugherty and Seidenberg 1994).(...)First, I present evidence that many, if not all, sound changes progress in lexical items as they are used, with more frequently used words undergoing change at a faster rate than less frequently used words. Then I examine alternating environments -- cases in which a sound in a particular word or morpheme is sometimes in the environment for the change to take place and sometimes not. In cases in which the targeted sound is at the edge of a word, the change can go through even where the sound is not in the appropriate phonetic environment and thus no alternation is produced. In such cases, we have evidence for the restructuring of the lexical representation of the word. However, when the alternating environment is inside of a word, the change can be retarded even in the appropriate environment, but eventually an alternation can be created, showing, again, restructuring of the lexical representation of the word. I argue that lexical representations are restructured gradually on the basis of actually occurring variants of a word and that postulating words and frequent phrases as the units of representation explains the development of word-level phonology. In addition, it will be argued that reference to the frequency with which words begin in consonants explains why a final word boundary often conditions changes as though it were a consonant.2. The frequency effect on sound changeOne of the aims of this chapter is to explore from a phonological perspective the size and nature of storage and processing units. I will present evidence that words and often longer units, such as frequent phrases, are the units of lexical storage. For the moment, however, I assume that words are the units of lexical storage. It is reasonable to assume that lexically stored words are in many ways like other mental records of a persons experience. First, there is no reason to believe that these memorial records have details and predictable features abstracted away from them (Langacker 1987; Ohala and Ohala 1995), and second, it is reasonable to believe that new experiences are categorized, to the extent possible, in terms of the already-stored record of past experiences (see Klatzky 1980).Each use of a word requires retrieval by the speaker and a