An attempt at methodologically founding a functionalist language theory, and more particularly a 'Functional Procedural Grammar' (a psychological production model for natural language). In the first chapter, the nature of studying the psychology of language is considered, and the implications for a conception of the science of language are discussed; the second chapter contains a phenomenology of linguistic behavior, more particularly of its functionality in communicative situations; the third chapter considers the concept of functional explanation, and a discussion of the Chomskyan formalist language theory, in particular with respect to its claims concerning the innateness of language.