Pursuing the Cascade Model
William Labov, University of Pennsylvania
Granted that language is a social fact, and not the property of any individual, it follows that a linguistic change is equivalent to the diffusion of that change. An understanding of language change therefore demands an understanding of the mechanism of diffusion. It has long been observed that linguistic features spread outward from an originating center, but in a progressively weaker form as distance increases.
The Atlas of North American English has traced the progress of a number of linguistic changes in progress (Labov, Ash and Boberg. in press). Of these, the Northern Cities Shift is the most likely candidate for a study of the cascade model, since it was first discovered in the major cities of Chicago, Detroit and Buffalo, and is now seen to cover a vast area involving many cities (71 cities with a population of 17,000,000 people in a territory of 33,000 square miles). This shift is a rotation of five vowels of English in the pattern of Figure 2.
Figure 2. The Northern Cities Shift
. The earliest and most extended elements of the change involve the raising and fronting of /ae/ and the fronting of /o/, followed by the lowering of /oh/ to low back position. The most recent changes are the lowering and backing of /e/ and the backing of /^/ to the position formerly occupied by /oh/.
The NCS is found in the North (the broken isogloss in Figure 3).a dialect region defined by the conditions that permit the NCS to occur . These are (1) the relatively back position of /ow/ (F2 of the nucleus < 1200 Hz) and a lax front nucleus for /ey/ (F2 of the nucleus < 2200 Hz).