 Some philosophers will no doubt respond that it is still imaginable that you and I are functionally identical in all relevant respects yet phenomenally different. But this claim presents a problem at least for those philosophers who oppose functionalism but who accept physicalism. For it is just as easy to imagine that there are inverted qualia in molecule-by-molecule duplicates (in the same external, physical settings) as it is to imagine inverted qualia in functional duplicates. If the former duplicates are really metaphysically impossible, as the physicalist is committed to claiming, why not the latter? Some further convincing argument needs to be given that the two cases are disanalogous. As yet, to my mind, no such argument has been presented. (Of course, this response does not apply to those philosophers who take the view that qualia are irreducible, non-physical entities. However, these philosophers have other severe problems of their own. In particular, they face the problem of phenomenal causation. Given the causal closure of the physical, how can qualia make any difference? For more here, see Tye 1995, Chalmers 1996).