ABSTRACT Diglossia poses a particular challenge to both grammatical and variation theory. Parametric theories of grammar must be compatible with the varieties of language in a diglossia, and statements of the variation in a diglossia should also integrate with the parametric properties of grammatical theory. As an approach to this problem, this research proposes a notion of "functional articulation", which allows a formal theory of grammar to be informed by language use patterns, by associating different grammatical features with different communicative attitudes. This notion will be developed in a detailed study of Sinhala diglossia. Sinhala has been chosen since it exhibits theoretically significant differences between its two main varieties, and intermediate varieties of language required to test hypotheses based on functional articulation. The study will examine samples of the language found in a wide range of contexts (e.g. textbooks, newspapers, broadcast news, advertising, personal and formal letters, sermons, speeches, literatures, etc.). Comparison and cross-referencing of selected texts will be facilitated by HyperCard. The distribution of several grammatical features over the different contexts will be analyzed in terms of their functional correlates and current grammatical theory, focusing on the relationship between agreement and case. The study will address the implications of functional articulation for modern theories of grammatical universals, and the implications for other diglossic language situations, education, and language teaching.