In Part I, a framework for discussion has been established in which the mechanisms of linguistic change have been identified. In Part II the interaction of these mechanisms will be exemplified by looking at selected developments in all four levels of language conventionally distinguished: writing-system and sound system (often linked together as 'transmission'), grammar and lexicon. In each case, outcomes traditionally assigned to one of these categories will be shown to be the result of dynamic interaction between intra- and extralinguistic processes. Thus, for instance, the Great Vowel Shift (the main example discussed in Chapter 5) will be shown to be the result of dynamic intralinguistic interaction between grammatical, phonological and lexical developments within an overall extralinguistic framework of sociohistorical change.
The theme of these four chapters, therefore, is to do with the interaction of linguistic levels with each other and/or with the world in which they are situated. Now the precise dividing-lines between the levels of language conventionally distinguished, of course, are extremely controversial amongst linguists. But for the present purposes it is convenient simply to take a fairly traditional view, whereby meaning ('semantics') is expressed through words ('lexicology') and grammatical rules ('grammar') themselves conveyed by sounds ('sound-system' or 'phonology') or writing ('writing-system'). The limitations of this model were already discussed in Chapter 1, and do not need repeating here. But there is one advantage: this communicative model draws attention to the truth that there are special relationships between lexicon and grammar on the one hand and between writing and speech on the other. Semantics would appear to have an independent, underlying status.
Many scholars would exclude consideration of writing-systems from their discussion of linguistic matters, either ignoring it completely or considering it part of a separate discipline; after all, the written mode undoubtedly