 How might an a posteriori physicalist respond to this objection? The obvious response is to reject the derivation view of the necessary a posteriori in favor of the non-derivation view. But this is just to say that if one wants to defend a posteriori physicalism, one will have to defend the non-derivation view of the necessary a posteriori. However, the non-derivation view is controversial, so it is not something that we can hope to solve here. (For discussion, see Byrne 1999, Chalmers 1996, 1999, Jackson 1998, Loar 1997, Lewis 1994, Yablo 1999, and the papers in Gendler and Hawthorne 2004)