Evans & Levinson (E&L) make an important point to cognitive scientists about language universals. The nature of language is seriously misrepresented by Chomskyan generative linguistics, which is all too often taken as the standard theory of language that must be accommodated by any interdisciplinary research in cognitive science. In particular, the Chomskyan emphasis on absolute unrestricted universals of grammatical structure flies in the face of overwhelming empirical evidence of the structural diversity of languages. This structural diversity has to be the starting point for any theory that attempts to come up with universals of language. I have only two additions to make to E&L's argument: First, their critique of syntax, the heartland of Chomskyan linguistics, is too timid; and second, the dynamic evolutionary approach to language that E&L advocate already has a lengthy pedigree in linguistics.
E&L's approach to syntax contrasts with their assertions about sound structure. E&L state that phonologists are abandoning the idea of a fixed inventory of possible human speech sounds in favor of a model where languages construct sound systems from fine phonetic details that vary substantially. But in syntax, they assume that word classes of the traditional sort (noun, verb, adjective, etc.) exist, and they respond to diversity by arguing that some languages do not take advantage of some of these classes or add others. This is very much like Jackendoff's notion of a syntactic toolkit, which the authors otherwise reject. In fact, E&L should abandon the assumption that nouns, verbs, and so on, have theoretical, cross-linguistic validity as part of a fixed inventory of word classes, just as they have abandoned the parallel assumption for sound inventories.
Linguists identify word classes by using syntactic criteria or tests. These criteria are the possible occurrence of words of a particular class in a set of grammatical constructions (including morphological inflectional contexts), and their inability to occur in other constructions. This is called the distribution of the words, or word class. But the fact of all languages, including English, is that the distribution of words is highly variable, so that there are no large coherent word classes in any language (see Gross Reference Gross1979). Thus, it makes no sense to say (as E&L do) that English words like willy-nilly and heeby-jeebies differ from ideophones in other languages in kind rather than degree, or that lunch and train in do lunch or take a train are just regular nouns; they are not (Wierzbicka Reference Wierzbicka1982). Instead, the only cross-linguistically valid – and language-internally valid – conclusion is that each construction defines its own word classes; words do not enter into a small number of large classes; and noun, verb, and so on, should be abandoned as word classes (Croft Reference Croft1991; Reference Croft2001; Reference Croft2007; Reference Croft2009).
This is not to deny that there are language universals constraining syntax, just as one cannot deny universals governing sound inventories; but they are not in the form of universal word classes found in traditional grammar and generative grammar. Instead, there are typological prototypes for parts of speech reflecting the preference of particular propositional acts (reference, predication, modification) for particular semantic classes; these are basically the same as E&L's clusters or attractors.
A similar argument applies to E&L's analysis of so-called subjects. A division of functions into topic, agent, and pivot is insufficient to reflect the diversity of encoding participants in clauses and the categorization of participant roles across constructions with different functions. Unlike word classes and propositional acts, there is no simple typological prototype to account for the diversity of participant encoding in clauses. Yet there are universal patterns that constrain the types of grammatical relations used for different construction types (Croft Reference Croft2001; Kazenin Reference Kazenin1994) and that constrain grammatical relations relative to each other in a clause (Croft Reference Croft1991).
The chief sense in which the dynamic, complex adaptive systems approach to language that E&L advocate is now emerging (as they put it) is that it is finally emerging from under the shadow of generative linguistics. Cognitive science must embrace language diversity and the consequences it entails for our understanding of the nature of language. But cognitive scientists need not wait for linguists to draw those consequences; there is much existing research to guide a nonlinguist cognitive scientist interested in the approach to language presented by E&L. A few examples are given here, linked to E&L's seven theses in their conclusion.
Linguistic diversity (thesis 1) is the basic starting point of typological analysis. An important omission in an article asserting the centrality of linguistic diversity is the existence of diversity (variation) within speech communities, not just across speech communities (see Labov Reference Labov1994; Reference Labov2001; Milroy Reference Milroy1992). Numerous databases and inventories of typological diversity (thesis 2) already exist. Although there are clusters (thesis 3) or attractors (thesis 4) governing the distribution of some linguistic diversity (typological prototypes), these are only some of the patterns of typological distribution that have been observed, as mentioned earlier. Greenberg (Reference Greenberg1969; Reference Greenberg1978a; Reference Greenberg1979) presents a model of language that shifts away from synchronic language states to language history (thesis 7). A detailed evolutionary theory of language (theses 2 and 5) which integrates variation across languages, within speech communities, and in language use is presented in Croft (Reference Croft2000a) and in Mufwene (Reference Mufwene2001; Reference Mufwene2008). Although this work is not coevolutionary, it balances the extensive recent work on the biological evolutionary origins of the language capacity by providing a cultural evolutionary framework for understanding language. Cognitive and functional constraints have been investigated in cognitive linguistics for a quarter of a century (theses 2 and 6; see Croft & Cruse [Reference Croft and Cruse2004] and Langacker [Reference Langacker2008] for recent overviews, and Tomasello [Reference Tomasello1998; Reference Tomasello2003b] for an introduction oriented to cognitive scientists).
Much of course remains to be done in evolutionary linguistics. Cognitive science can draw on these strands of linguistic theory and empirical discovery, and evolutionary linguistics can draw on the rest of cognitive science for a better understanding of the factors that motivate speakers' creation and use of the linguistic structures that are found in the world's languages – before they disappear.
