In Chapter 3, it was observed that linguistic variation arose in two ways: through divergence from a common inherited ancestor, and through contact with other varieties or languages, that is, through the interaction of intra- and extralinguistic phenomena. In the last chapter, the standardisation of written English in particular was placed within its extra-linguistic and intralinguistic context. In this chapter, the attention shifts to the transmission of the spoken mode, that is, phonology and phonetics, and it will be observed that dynamic interaction between extra- and intralinguistic processes is similarly of key importance. In short, it is argued here that a given sound-change is the result of a number of factors, both intra- and extralinguistic, acting in combination.
Historical linguists have traditionally focused their attention on soundsystems-that is, phonology-rather than phonetic detail, and there are good reasons for this. If we leave aside the science of phonological reconstruction, the history of sounds, before the widespread use of mechanical and electronic methods of recording language in the twentieth century, has to depend on the study of written language. As was noted in Chapter 2, alphabetic writing-systems, such as that in which English is and has been recorded, are designed to distinguish the smallest meaningfully distinctive units of language, and are thus broadly phonemic in the way in which they map the spoken mode-even though, given spelling-traditions, this mapping may reflect an earlier stage in the language's history.
Linguists have traditionally compiled a language's or variety's phonemic inventory by noting the existence of 'minimal pairs', that is, pairs of words in which a difference of a single sound in an identical phonetic environment indicates a difference of meaning. To distinguish allophones (i.e. varying realisations of phonemes) in orthography is in principle uneconomical and would be communicatively confusing. Efficient written communication therefore depends on a correlation between grapheme and phoneme. As a result, we can expect at least a tendency for allophonic variation not to be reflected in the written mode.