Towards the end of the discussion we began to discuss what was involved in conceiving of the shombie world. Dave seemed to think that doing so involved conceiving of a possible world where physicalism was true. This amounts to the claim that <>(P–>Q), i.e. that it is possible that it is necessary that the physical facts of our world entail that there are qualitative facts. In S5 if something is possibly necessary it is necessary (this is intuitive since if there is one possible world where a necessary truth is true then, if it is to be necessary, it must be true at all worlds including the actual one). This way of reading the shombie/illuminati argument has it more like contemporary versions of the ontological argument.
This is a bad way of thinking about the shombie argument since once we start to think about the possibilities of necessities we have to think about the entire space of possible worlds and our intuitions about how this space will turn out become very untrustworthy. I agree with Dave that we are better off just trying to conceive of one specific possible world. So to conceive of the shombie world all we need to do is to conceive of one possible world where physical facts entail qualitative facts (or alternatively where qualitative properties just are physical properties). That world is negatively conceivable (call this the illuminati claim) and plausibly positively conceivable (call that the shombie claim). Now is this a world where physicalism is true? Well that depends on your views about the necessity of identity statements. As is well know there is a very simple proof of the necessity of identities. The following is taken from Kripke’s Identity and Necessity,
3. (x)(y) (x=y)–>((x=x)–> (x=y))
4. (x)(y) (x=y)–> (x=y)
The first premise says that if x and y are the same thing then if x has a property y has that property also. The second premise just says that it is necessary that every object is self identical. The third premise is a substitution instance of 1. What it says is that if x and y are the same thing then if x has the property of being necessarily self identical then so does y. From that we get four since we know that (x=x) is true (though I suppose one could block the argument if they denied this…maybe someone like Dave will do this?)
At any rate 3 makes clear the point I am trying to make. The postulated identity in the antecedent is one thing and the hypothesis that if there is an identity then it is necessary is another. Thus we do not have to conceive of the shombie world as one where it is possible that some necessary truth is true. We simply need to conceive of a world where P=Q for some subset of the total physical facts and some qualitative fact. It is true that this by itself will not rule out dualism. The dualist might counter that the shombie world is conceivable but dualism still might be true of our world (though as a side note this is a much less attractive view for the dualist since if they admit that it is possible to have shombies then we probably should be focused on empirically finding out which is true) but this can be ruled out independently with the above argument.
Towards the end of the discussion Barbara Montero brought up the possibly of what she called “blocker worlds”. A blocker world is one where there are illuminati, or shombies, but in addition there are nonphysical properties or entities that ‘block’ the qualitative properties. Thus in this world there are physical duplicates of us, the physical facts entail that there are qualitative facts, but the nonphysical blockers block these facts. Barbara and dave seemed to think this was a problem for physicalism. Jim Pryor suggested that it wasn’t since even though in this world there were no qualitative properties if one just took the physical facts by themselves we would get qualitative facts. Kati seemed to think that this world wouldn’t be a world where there was a minimal physical duplicate of me since a minimal physical duplicate is one that has only the properties that I do and nothing else. Others were pressing here suggesting that blocker world folk are minimal physical duplicates because they have all of the very same physical properties as I do. I seemed to think that these creatures wouldn’t really even be physical duplicates of me since the blockers were interfering with the physical processes in such a way as to make a physical difference (how else could they block the qualitative properties? Barbara suggested that the blockers were like aspirin, but this works by effecting physical processes…I mean clearly there is a physical difference between someone who took aspirin for a headache and someone who did not.)
Anyway, I have to get ready to head out to Benji Kozuch’s cog sci talk at the Graduate Center….