Age as an external constraint has most often been taken for granted as a factor with a solid biological basis. Its sociocultural context has not been studied much, and, as this study suggests, more information is needed about the linguistic behaviour of people of different ages. Historical data provide opportunities for longitudinal studies of some individuals' language from relatively long periods of time.
This chapter suggests that morphosyntactic changes spread in the speech community in both a communal and a generational manner. It has become evident that some people change their language during their lifetimes while others do not. Why this happens is a challenging research problem. Reasons can be sought in the personal histories of individuals - a matter that emphasizes the role of micro-level studies. A step in this direction has been taken in our analysis of the linguistic behaviour of individuals during ongoing changes. The proportion of people who participate in each change varies with time. The highest incidence of a variable grammar fluctuates and does not coincide with the same area in the S-curve of the different changes.
In this chapter we hope to have shown that the apparent-time analysis of historical data can provide new information about the way linguistic changes diffuse among people, hence addressing the general problem of transition. One advantage of the combination of real- and apparent-time approaches is theoretical: the validity of the apparent-time construct can be tested. Our data show that, although the apparent-time analysis often correctly predicts the progression of an individual change, counterexamples also occur. The existence of counterexamples cannot be explained by age models but has to be analysed with other tools, both linguistic and nonlinguistic. In the end, age is just one dimension in an individual's social space.