In this chapter, our focus of interest will be on syntactic variation and change both within the speech community and within the individual speaker. We will mainly be concerned with the question whether certain patterns of variability target the grammatical knowledge of the speakers or whether they are rather a reflex of how this knowledge is put into use. The former would be the case when UG-constrained parametric differences are at stake which, in addition to language-universal principles, constitute the speakers’ core grammar (cf. Chomsky 1981: 7). Such cases of parametric variation can be observed not only when comparing different languages. Parametric differences might also be relevant, as we will lay out below, when comparing varieties of a single language such as dialects, sociolects or registers. Finally and most importantly for the purpose of this book, syntactic differences between two diachronic states of a language or variety could also reflect an underlying parametric change. We assume that the core grammar constitutes a homogeneous knowledge base shared by the speakers of a certain language or variety. Variability at this level would hence indicate the presence of different grammatical systems, either synchronically or diachronically.

The second possibility relates to variation at the level of language use. This can be observed, for example, in domains where the grammar allows for different surface realizations of a single structural base. This kind of variation is typically conditioned by a multitude of environmental factors which may be of either a linguistic, a pragmatic or an extralinguistic, i.e. social or stylistic, type.

Both parametric variation and variation in language use may result in the same surface effects. The major methodological challenge for the analyst is hence to disentangle for each instance of morphosyntactic variation which of these two types of variation is actually involved. In the following, we will examine a number of variable phenomena and discuss whether they can more plausibly be ascribed to parametric variation, i.e. to differences relating to the mental representation of the speakers’ grammatical knowledge, or whether they rather reflect variation in use.