Abstract Noam Chomsky, the founding father of generative grammar and the instigator of some of its core research programs, claims that linguistics is a part of psychology, concerned with a class of cognitive structures employed in speaking and understanding. In a recent book, Ignorance of Language, Michael Devitt has challenged certain core aspects of linguistics, as prominent practitioners of the science conceive of it. Among Devitt's major conclusions is that linguistics is not a part of psychology. In this thesis I defend Chomsky's psychological conception of grammatical theory. My case for the psychological conception involves defending a set of psychological goals for generative grammars, centring on conditions of descriptive and explanatory adequacy. I argue that generative grammar makes an explanatory commitment to a distinction between a psychological system of grammatical competence and the performance systems engaged in putting that competence to use. I then defend the view that this distinction can be investigated by probing speakers' linguistic intuitions. Building on the psychological goals of generative grammar and its explanatory commitment to a psychological theory of grammatical competence, I argue that generative grammar neither targets nor presupposes non-psychological grammatical properties. The latter nonpsychological properties are dispensable to grammarians' explanations because their explanatory goals can be met by the theory of grammatical competence to which they are committed. So generative grammars have psychological properties as their subject matter and linguistics is a part of psychology.