In this article, I investigate the implications of socially meaningful sociolinguistic variation for competence grammar, working from the point of view of HPSG as a kind of performance-plausible sign-based grammar. Taking data from African American Vernacular English variable copula absence as a case study, I argue that syntactic constraints and social meaning are intertwined. I present an overview of the literature on social meaning, discuss what grammars are models of, and argue that in order to model socially meaningful variation, competence grammars need to be extended to include social meaning, precompiled phrases, and probabilistic or frequentistic information. I then explore different heuristics for defining the boundaries of competence grammar and discuss the commonalities between the proposed additions and the kind of linguistic knowledge which is generally assumed to comprise competence grammar.