 The dominant paradigm within cognitive science involves postulating representational states at the subpersonal or subdoxastic levels (for philosophical discussion see Stich 1978, Davies 1989). Examples are the representational states implicated in tacit knowledge of the rules of syntax. It is a fundamental tenet of a broadly Chomskyan approach to syntax that speakers are credited with tacit knowledge of a grammar for their language and that this tacit knowledge is deployed in understanding spoken language. Yet when linguists give theoretical specifications of the syntactic rules contained within the grammar they frequently employ concepts that are not in the conceptual repertoire of the language-user. That is, the language-user is ascribed knowledge of rules formulated in terms of concepts that he does not possess. A similar point holds for the representational states postulated in computational theories of vision such as that put forward by Marr (1980). The contents of such states are formulated in terms of concepts (such as the concept of a zero-crossing) that are clearly not possessed by the average perceiver.