A rate of change index for language

Although the rates of changes in language are customarily described in relative terms, this paper presents a method of quantifying the rate of a given change during a specific time period. Utilizing the results of recent studies of sound change in progress, the Rate of Change Index is applied to the data for the purpose of indicating precisely the speed of these changes. Also measured in this manner are the rates of change of a variable in different phonetic contexts and among different social classes. The comparisons made here lend support to two important theories: that linguistic change follows an S-curve and that change proceeds more rapidly in urban than in rural areas. The Index contributes, then, to an inductive model of sociolinguistic change. It is also suggested that the Index can be applied to syntactic and lexical changes as well. (Linguistic change, Sociolinguistics, Phonology.) Scholarly interest in the rate of language change can be traced back over a century; Hymes (1973) has recently sketched a history of nineteenth century interest in lexicostatistics and glottochronology.1 Perhaps the best known attempt to specify quantitatively the rate of change is that of Morris Swadesh, 'to all intents and purposes the inventor of lexico-statistics and glottochronology in our time,' who used 'basic vocabulary as an index of diversity due to time, (Hymes 1973: I24). To investigate rate of linguistic change one can focus on an entire language or a sector of language such as phonology, syntax or basic vocabulary (as did Swadesh) or on specific instances of documented changes. The time span considered can be across several centuries or as few as two demographic generations. Perhaps because of the resistance of many linguists to quantitative measurement of language change, especially regarding glottochronology, current historical textbooks either ignore the issue or present a brief sketch of glottochronology, pointing out problems inherent in the method (Antilla 1973: 396-8). What we usually find are impressionistic statements about 'fast' and 'slow' changes (Cassidy 1973) or a claim that change spreads gradually (King