Quantitative approaches to diachronic corpus linguistics

English Historical Linguistics has a rich and long-standing tradition of corpus-based work (cf. the surveys in Rissanen 2008, Kytö 2012). Resources such as the HELSINKI corpus, the BROWN family of corpora, and ARCHER have spawned active research programs for the study of lexical and grammatical change, both long-term (Curzan 2008) and short-term (Mair 2008). In addition, corpus resources inform the analysis of diachronic variation in genres (Mair & Hundt 1999), registers (Biber & Gray 2011), and varieties (Tagliamonte 2006a). The present chapter will discuss a currently developing line of research which uses the methods of quantitative corpus linguistics for the analysis of diachronic corpora. This research program draws on, and is informed by, the aforementioned areas, but at the same time, it uses particular kinds of data and handles that data in specific ways that merit discussion. Diachronic corpora are understood here as textual resources that represent comparable types of language use over sequential periods of time, thus comprising at least two periods, as in the Diachronic Corpus of Present-Day Spoken English (DCPSE, Wallis et al. 2006), but typically many more, as in the Corpus of Historical American English (COHA, Davies 2010), a monitor corpus which at the time of writing samples 21 sequential decades of language use. The English diachronic corpora that are currently available represent different varieties and text types and vary in their respective time depths, but it is a design feature of most diachronic corpora to hold the type of text constant, so that diachronic language change within a given text type may be studied with as few confounding factors as possible. Quantitative corpus linguistics (Biber & Jones 2008) is a research tradition in which research questions are formulated in such a way that frequency counts from corpora may provide answers. Quantitative corpus work thus often engages in hypothesis testing, so that a testable empirical question (e.g. 'Have adolescent women been leading the development of the quotative be like in Tyneside English?') may receive an answer in terms of either 'yes' or 'no'. Of at least equal importance are so-called exploratory techniques, which are designed to transform a complex dataset into a summary (and often visual) representation (which may then be interpreted by the analyst and that may in turn lead to the formulation of hypotheses). To give an example, Szmrecsanyi (2010) studies the use of genitive constructions in different text types of British and American English in the 1960s and the 1990s, exploring whether there are changes that could be seen as Americanization or colloquialization (cf. Mair 2006). The frequency counts that enter quantitative corpus studies often represent token frequencies, but a much wider variety of measures is routinely used, including measures of type frequency, dispersion, and collocation. The main point of this chapter will be an overview of how the two, diachronic corpora and quantitative corpus linguistics, are put together in fruitful ways. Quantitative studies of how units of linguistic structure change across corpus periods can address questions of more general linguistic interest, including the following ones: