The discussion throughout this paper is devoted to answering the question: What is the nature of our knowledge of language and what theoretical assumptions does the answer entail for linguistic description? Discussed are--(1) what it means to know a language, (2) the distinction between linguistic competence and performance, (3) justification of the transformational model as the theory of linguistic competence, (4) rule-governed creativity versus simple analogy, (5) underlying and superficial structures, (6) transformational grammar and its organization, (7) the theory of language and the grammar of a language, (8) the language acquisition device and the construction of the theory of language, (9) evaluation measure, and (10) justification of grammars. A short bibliography is appended. (DO)