Two mental states can share identical causal roles yet differ in their proper functions.

The compatibility of functionalism and representationalism is not evident on its face, though a number of prominent contemporary philosophers appear to embrace both positions (e.g., Fodor 1968, 1975, 1981, 1990; Armstrong 1973; Harman 1973; Lycan 1981a, 1981b; Stalnaker 1984; Lewis 1994). As Millikan (1984), Papineau (1984), and others have suggested, it seems one thing to say that to believe is to be in a state that fills a particular causal role, and it seems quite another to say that beliefs