The discussion of Richard Chappell’s post Understanding (Zombie) Conceivability Arguments: Part II over at Philosophy, etc has prompted me to clarify the sense in which I take (P & ~Q) to be contestable and the reasons whyI take the primary and secondary intensions of statement in Q not to be identical; as it turns out the two claims are related.
We first start with the primary and secondary intensions of a statement. Let’s take our old standby ‘water is H2O’ and our two ways of considering possible worlds as either actual or counter factual. So, ‘water is H2O’ is true when we consider any possible world as counter factual. This is because ‘water is H2O’ is an a posteriori necessity. There are no worlds, considered as counter-factual, where water isn’t H2O. But there are possible worlds, which if we consider as actual instead of counter factual, ‘water is H2O’ comes out false. So, take Twin Earth. On Twin Earth ‘water is XYZ’ is true and so when we consider Twin Earth as actual ‘water is H2O’ is false. That is to say that if Twin Earth were the actual world ‘water is not H2O’ would be true (because ‘water is XYZ’ is true there). What we have here is the makings of the distinction between primary and secondary intensions. The primary intension of a statement is given by asking whether it is true or false at possible worlds considered as actual while the secondary intension of a statement is given by asking whether it is true or false at possible worlds considered as counter factual. In effect then the primary intension of a statement is given by some kind of reference fixing description and then we determine whether the statement is true or not by taking a possible world and letting the description fix the reference at that world and the secondary intension of a statement is given by assigning the actual reference of the terms in question and holding that fixed as we vary our counter factual worlds.
Primary and secondary conceivability are then defined in terms of the kind of intension at work. So, take ‘water is not H20’. Chalmers accepts that there is a sense in which this is not conceivable. This is the sense in which we give ‘water’ the reference that it actually has. Then ‘water is not H20’ is equivalent to saying ‘H20 is not H20’ which is a contradiction. But this is to use secondary conceivability. ‘Water is not H2O’ is still primarily conceivable since if we consider Twin Earth as actual it will be true. This is because we assign ‘water’ just the reference fixing description and so to say that water is not H2O is just to say that ‘the stuff picked out in the same way we pick out H2O is not H2O’ which is true at Twin Earth. This captures Kripke’s way of putting it. When we think that we are conceiving of water not being H2O were are really conceiving of a person who is in the same epistemic situation as we are when we pick out H2O but isn’t picking that stuff out (i.e. Twin Earth). Now, Chalmers continues, the zombie argument relies only on primary conceivability, not secondary conceivability; in fact Chalmers himself accused my zoombie argument of relying on secondary conceivability and not primary conceivability. I think my response at the time isn’t as good as it could be because it focused on P and not Q So let me try and restate the case.
A crucial premise of Chalmers’ argument is that when it comes to pains and other phenomenal properties their primary and secondary intensions are identical. What that means is that the statements in question pick out the same property no matter whether we consider the world as actual or counter factual. This is supposed to capture Kripke’s claim that it is impossible for there to be someone in the same epistemic situation as someone who was in pain and yet for that person not to be in pain (and that it is impossible for there to be a person who was in the same epistemic situation as someone who wasn’t in pain and yet to be in pain. There is no appearance/reality distinction when it comes to pains. So then the upshot here is to try to show that there is a difference between the way ‘water is not H2O’ works and the way ‘pain is not C-fiber firing’ works that preserves Kripke’s general idea but is made precise by the 2-D framework. Kripke’s basic idea was that when we think that some identity is contingent what is really going on is that there is some identity statement involving a description that is contingent but this can’t be the way we explain away the seeming contingency of ‘pain is C-fiber firing’ since there is no alternate contingent identity involving a description in the case of pains. This translates into the 2-D framework as the claim that Kripkean a posteriori necessities have a contingent primary intension (i.e. ‘water isn’t H2O’ comes out true at some possible world considered as actual) but ‘pain isn’t C-fiber firing’, according to physicalist, has a necessary primary intension (there are no worlds considered as actual where this comes out true).
But what are we to make of this claim? Is it really the case that the primary and secondary intensions of ‘the painful stuff is C-fiber firing’ are identical? Or another way of asking the question; can the painful stuff fail to be c-fiber firing at some possible world considered as actual even though the painful stuff picks out C-fiber firing here? The answer is arguably yes! This is something that may be surprising but it is arguably shown to be true by empirical results. In particular cases of Dental Fear show that we can pick out mental states as painful which are not pains. Pain Asymboilia also, arguably, shows that we can pick out pain states without picking them out as painful. So the primary intension of ‘pain is not C-fiber firing’ is contingent. There is a possible world, say, where the painful stuff is ABC, where ABC is some distinct property from C-fiber firing, and if that world were actual it would be true that pain is not C-fiber firing. But does that world threaten physicalism? Obviously not. It is not physically identical to our world so is no threat. What needs to be shown is that there is a possible world where you have C-fiber firing and no painful stuff. Is there one? Well, obviously there might be one that is physically distinct from ours (that is, a world that was NOT a micro-physical duplicate of ours, say with different laws of physics there, might have C-fiber firing and no painful stuff and if that world were actual then it would be true that ‘c-fiber firing isn’t pain’) but again this world is not threat to physicalism. But of course (P & ~Q) is supposed to describe a world that IS micro physically identical to ours and which lacks qualitative properties. But this clearly isn’t conceivable on the present account. To see this, compare the water=H2O case. Given that the watery stuff is H2O in the actual world we know that in a world micro-physically identical to ours is a world in which H2O is picked out by ‘the watery stuff’. So too, then, if pain=C-fiber firing in the actual world then we know that any world micro-physically identical to ours is a world in which C-fiber firing is picked out by ‘the painful stuff’. So IF physicalism is true of our world then zombies are not conceivable. But this is not to rely on secondary conceivability. This is to rely of the non-identity of the primary and secondary intensions of ‘pain is not C-fiber firing’ in just the same way as we do in the water/H2O case. This is why my view is in the Kripkean-tradition, and so akin to type B physicalism but not wholly so.
Notice that the upshot of this is that when the dualist says that (P & ~Q) is semantically neutral they are either wrong or do not threaten physicalism. When they go to explicitly fill in the place holder ‘~Q’ with statements like ‘RB is consciously having a pain’ they assign a semantics to terms like ‘pain’ where the primary and secondary intensions are identical, whereas a physicalist like me will assign those terms a semantics just like other natural kind terms (where these intensions are not identical). If you really were to remain neutral on this semantic issue the conceivability of (P & ~Q) is no threat to physicalism (since you need the premise (PI=SI) to make the argument go through). So to get the zombie argument off the ground you must assume a certain semantics for the terms in Q, just as to get the zoombie argument off the ground you have to assume a certain semantics for NP (namely one that stipulates that there are no qualitative properties in NP. This nicely mirrors the zombie argument where the dualist has to stipulate that there are no physical properties in Q). It may be the case that this is more obvious in the zoombie case but it still helps to expose the same flaw in teh zombie argument.