In this paper, we argue that under certain prevalent interpretations of the nature and aims of cognitive science, theories of cognition generate a forced choice between a conception of cognition which depends on the possibility of a private language, and a conception of cognition which depends on mereological confusions. We argue, further, that this should not pose a fundamental problem for cognitive scientists since a plausible interpretation of the nature and aims of cognitive science is available that does not generate this forced choice. The crucial difference between these interpretations is that on the one hand the aim of theories of cognition is to tell us what thinking (etc.) is, and on the other it is to tell us what is causally necessary if an intelligent creature is to be able to think. Our argument draws heavily on a Wittgensteinian conception of philosophy in which no philosophical theory can explain what thinking, perceiving, remembering, etc. are, either. The positive, strictly therapeutic, purpose of a philosophy of cognitive science should be to show that, since the traditional problems which constitute the philosophy of mind are chimerical, there is nothing for philosophical theorizing in cognitive science to achieve.