Code-Switching and the Variable Grammar Hypothesis: Evidence from Moroccan Arabic–French Bilinguals

This study investigates whether grammatical models of code-switching grounded in informal, linguist-generated judgments hold up when tested against formal acceptability ratings from bilingual speakers with varying second language (L2) proficiencies. Specifically, it evaluates the Functional Parameter Constraint (FPC), a syntactic model that predicts code-switching must preserve the hierarchical structure of functional heads. To test the FPC’s generalizability beyond fluent bilinguals, 36 Moroccan Arabic–French bilinguals ( split into high and low L2 proficiency groups—rated the acceptability of 23 constructed sentences, some adhering to the FPC and others violating it. Ratings were collected using a three-point scale, then analyzed quantitatively through match-rate comparisons and two-proportion z-tests, followed by a qualitative interpretation of the results. The results reveal that high-proficiency speakers aligned more closely with FPC predictions than low-proficiency speakers, but that neither group fully conformed to the model. In several cases, low-proficiency speakers produced acceptability patterns that contradicted the FPC, and even high-proficiency ratings diverged from those recorded in previous naturalistic corpora. These discrepancies suggest that grammatical judgments are influenced not only by linguistic structure but also by speaker proficiency and the elicitation method used. These findings challenge the assumption that code-switching constraints derived from fluent speakers can be applied universally. They underscore the importance of formal, experimentally controlled methods in bilingual syntax research and support the adoption of gradient models that account for speaker variability. The study contributes to refining grammatical theories of code-switching and highlights the need to incorporate L2 proficiency and methodological rigor into their formulation.