 The first to be considered are the “absent” and “inverted” qualia objections most closely associated with Ned Block (1980b; see also Block and Fodor 1972). The “inverted qualia” objection to functionalism maintains that there could be an individual who (for example) is in a state that satisfies the functional definition of our experience of red, but is experiencing green instead—and similarly for all the colors in the spectrum. It is a descendant of the claim, discussed by philosophers from Locke to Wittgenstein, that there could be an individual with an “inverted spectrum” who is behaviorally indistinguishable from someone with normal color vision; both objections trade on the contention that the purely relational characterizations in question cannot make distinctions among distinct experiences with isomorphic causal patterns. (Nida-Rümelin, 1996, argues that the science of color vision leaves open the possibility that there could be functionally equivalent red-green “inverts”, but even if inverted qualia are not really an empirical possibility for human beings, given certain asymmetries in our “quality space” for color, and differences in the relations of color experiences to other mental states such as emotions (Hardin 1988), it seems possible that there are creatures with perfectly symmetrical color quality spaces for whom a purely functional characterization of color experience would fail.)