Word Classes in Studies ofPhonological Variation: Conditioning Factors or Epiphenomena?

Typological studies have demonstrated that all languages possess different parts of speech and, for instance, cross-linguistically all languages distinguish nouns from verbs. In fact, so pervasive is this linguistic truth, that, as noted by Vigliocco, Vinson, Druks, Barber, & Cappa (2011), it is widely maintained that grammatical category is itself cognitively separable from other types of linguistic information. Indeed, grammatical class has been argued to be a type of linguistic information independent of other pragmatic or semantic features and to be an active, organizing principle of the lexicon. Traditional models of speech production (e.g.; Levelt 1989) suggest fundamental cognitive processing differences required in the production of different word classes such as function and content words, and such processing differences may, thus, in turn affect production (Jurafsky, Bell, & Girand 2002, Phillips 2006, Gahl 2008). Precisely what the mechanisms underlying the production of word classes are, or how they operate upon phonological form, however, has not been entirely established. In line with this view, studies of phonological variation and change include word or grammatical class as an independent linguistic variable thought to constrain variation. Significant word class effects have been noted in a wide range of studies (e.g.; Labov 2001). Often it is found that rates of reduction for a specific linguistic variable under investigation correlate significantly with different grammatical classes of words, and this is true both diachronically (e.g.; Phillips 2006) and synchronically (e.g.; Jurafsky, Bell, Gregory & Raymond 2001, Clark & Trousdale 2009). In Spanish, word class effects have been noted in studies on a multitude of phonological variables such as word-final /n/ velarization (Hoffman 2010), word-final /s/ realizations (Brown & Torres Cacoullos 2003, Valentin-Marquez 2006, Poplack 1980), intervocalic /d/ weakening (Moya Corral & Garcia Wiedemann 2009), and hiatus resolution (Alba 2008), to name just a few. Clearly, word classes matter. However, despite its frequent use as a factor in linguistic analyses, few attempts are made to explicitly state by what mechanism a word class can actively constrain variation. Indeed, the focus of this current paper will be to question whether, in fact, such a mechanism operates, and, alternatively, whether word class effects can be characterized as secondary symptoms of unidentified correlations in the data with variables known to promote reduction. Such correlations are known to exist for other linguistic predictors of reduction such as word frequency, but have not been studied for word classes. The assertion that word class effects may be merely epiphenomenal is in line with viewing grammar as emergent (Bybee 2010). Word class distinctions, such as the difference between a noun and a verb, can be argued to arise in language as a result of differential semantic and pragmatic uses. Lexical representations of words (Bybee 2001), thus, are not independent of grammatical information and no categorically distinct representations or processes are presumed for separate word classes. Word class identity can be seen as indistinguishable from the significantly different patterns of use that naturally arise in discourse for words from different classes (Bybee 2002). Indeed, it is precisely such