In my talk, I bring together two research strands that rarely interact and might even seem incommensurable, namely sociolinguistic approaches to linguistic fluidity and multi-competence on the one hand, and structural approaches to linguistic coherence and grammatical systems on the other hand.

Current sociolinguistics approaches typically take a perspective of language as a fluid and dynamic resource realised through such practices as (trans-/poly-) languaging. Such approaches are often critical of attempts to identify and distinguish separate linguistic varieties, rejecting the idea of bound “languages” and deconstructing distinct language systems and named languages as an invention of European nation states. Against this background, a view of an overall linguistic “multi-competence” replaces assumptions about competences in several distinct languages.

In stark contrast, grammatical analysis in theoretical linguistics typically relies on the implicit assumption of discrete and coherent linguistic systems, be it at the level of languages or of varieties/dialects. Such analyses target grammatical structure and systematicity within linguistic systems, and cross-linguistic interactions including transfer between different systems.

I show that we can reconcile insights from these two strands in a linguistic architecture that takes communicative situations as the core of linguistic systematicity, and integrates them into grammatical representations. Under this view, communicative situations are the basis for linguistic coherence and grammatical systems, and can support the emergence of languages as sociolinguistic indeces. I discuss this approach for four domains that illustrate different aspects of linguistic diversity and fluidity: urban markets, minority/heritage language settings, multiethnic adolescent peer-groups, and digital social media.