This project focuses on implications for linguistic theory of a phenomenon found in some Basque dialects known as allocutivity—morphological agreement with non-participant addressees. Current syntactic literature is besotted with this phenomenon for the privileged access it offers into syntactic representations of Speaker and Hearer speech act roles, which are encoded syntactically in all human languages. Basque is special as a laboratory variety for exploring the syntax of speech act roles in that no other language so far described approximates Basque in terms of (i) the direct morphological evidence that it offers about the relationship among allocutivity, thematic addressees and vocative expressions, and (ii) its rich patterns of cross-dialectal/cross-speaker variation revealing loci of formal variation. The principal goal of this project is to describe three facets of this phenomenon wholly ignored in extant formal and psycholinguistic descriptions: (i) the nature of cross-dialectal variation and change in the syntax of allocutivity; (ii) the relationship of allocutivity to vocative expressions across dialects; and (iii) differences in grammatical constraints across levels of politeness marking. The project team —spanning diverse fields of expertise and from several different institutions— will gather two kinds of data to address these issues: survey data through a web-based application (N ?500), and interview data with a smaller set of participants (N ?120). Data will be made publicly accessible through an online data dashboard and through summaries in peer-reviewed publications.