Deprioritizing the A Priori Arguments against Physicalism

Richard Brown

ABSTRACT:

In this paper I argue that a priori arguments fail to present any real problem for physicalism. They beg the question against physicalism in the sense that the argument will only seem compelling if one is already assuming that qualitative properties are nonphysical. To show this I will present the reverse-zombie and reverse-knowledge arguments. The only evidence against physicalism are a priori arguments, but there are also a priori arguments against dualism of exactly the same, but opposite variety. Each of these parity arguments has premises that are just as intuitively plausible, and it cannot be the case that both the traditional scenarios and the reverse-scenarios are all ideally conceivable. Given this only empirical methods will advance the debate between the physicalist and the dualist. Furthermore, by the time a priori methodology will be of any use it will be too late.

Roughly speaking, physicalism is the view that only physical things exist.[1] Physical things are those things that are postulated by a completed physics. Currently they include quarks, electrons and various forces but these may or may not be part of the completed theory. To say that only physical things exist is not to deny that tables, chairs, cars, and brains exist. They do but only because they are composed of physical things. To put this a bit more formally the physicalist holds that a complete microphysical duplicate of the actual world is a complete duplicate simpliciter. So, the physicalist in the philosophy of mind holds that a complete microphysical duplicate of me would be a complete qualitative duplicate of me as well. Given this, and some other assumptions, the physicalist is committed to being able to deduce that these things exist from a completed physics (Jackson and Chalmers XXXX).[2] I am a physicalist but I do not intend, in this paper, to argue that physicalism is true. Rather I intend to argue for the more modest claim that no current a priori argument shows that it is false. This does not mean that physicalism is in fact true. There may be empirical arguments against it or perhaps other a priori arguments. Currently the empirical case for physicalism is very strong, but that may change. There are other a priori arguments against physicalism, like Kripke’s well known modal argument, but all of these rely on the same intuitions as found in the knowledge and zombie arguments. What we say here can be extended to them easily. All of this taken together shows that the case fore physicalism is quite strong but here I want to focus more on the a priori case against physicalism.

I am willing to grant that physicalism could be shown to be false a priori (if in fact it is false); of course I also hold that it can be shown to be true a priori (if in fact it is true).[3] To see how, it is important to recognize that something is a priori just in case it can be known independently of experience and this introduces a new modality (Kripke 1981). While it is true that if we idealize the rationality and knowledge of the agent all things would be immediately be a priori it does not follow that to us now these things are known a priori or that the way we first come to know them is via a priori means. For instance, before the modern theory of chemistry it was a priori that the totality of physical facts entail that there are water facts and this could be known a priori but people in 1505 were not in a position to know that this was the case. They could have known that a certain conditional statement would have been true --if the world turns out a certain way then water facts are entailed by physical facts, if it turns out another way then not—but could not have known which of these it was. The way we came to know which was actually the case was empirically and so this is an a posteriori discovery but now, we can see that water facts are entailed by the physical facts. Indeed we can see that this is a priori and that it is a priori false that a world physically identical to ours could lack water.

Given this I can restate the aims of my argument more precisely. I hold that we are not yet in a position to see whether it is a priori true that physicalism is false (or that is true) and that the way we will actually come to know which is true will be via empirical means. An idealized agent would know which, but we are not idealized agents. I am willing to grant that we can make some kinds of claims about what ideal reasoning would look like but this is not the main problem in my view. The problem comes from our lack of empirical knowledge. As the water/H2O case shows, to be in a position to see that the water facts are entailed by the H2O facts required that we know that water is actually H2O. Therefore in order to know whether physicalism is true or false a priori requires knowing whether it or dualism is actually false. Once we know that we will be in a position to a priori deduce, or not, the qualitative facts from the physical facts. But, of course, once we know whether physicalism is actually false we won’t need a priori methods to see that. It is therefore the case that from where we are now, only empirical work will advance the debate between the physicalist and the dualist.[4] From where we are now offering a priori arguments are of little to no use for showing that physicalism is false. All it can do, I argue, is to let one know where one stands with respect to the question but cannot answer it.

What results is a position that falls under what is known as type-C physicalism but not quite of the usual type. To make this argument I will present 4 parity arguments, two of them familiar from the literature two of them not. Afterwards I will turn to examining a number of objections, which will help clarify and defend the claims made here.

1. The Reverse-Thought experiments

1.1. Zoombies

Zoombies are creatures that are nonphysically identical to me in every respect and which lack any nonphysical phenomenal consciousness.[5] Put a bit more formally we can say that where NP is the totality of the nonphysical facts about me now and Q is some qualitative fact about me, say that I am now seeing green, it is conceivable that NP & ~Q obtain. That is to say that I can conceive of all the actual nonphysical properties being instantiated, in just the way they are now, and yet not including qualitative properties. There is no obvious contradiction that emerges from conceiving of all actual nonphysical properties being instantiated and yet not including phenomenal properties. From this it follows, in exactly the same way as in the zombie argument, that dualism is false. Zoombies closely resemble zombies. The traditional zombie is a creature that has everything I do physically but lacks phenomenal properties, a zoombie is likewise a creature that has everything I do nonphysically but lacks phenomenal properties. We can formalize the zombie argument as follows,

1. NP and ~Q is conceivable

2. If (NP & ~Q) is conceivable, then (NP & ~Q) is possible

3. If (NP & ~Q) is possible then dualism is false

4. Therefore dualism is false

This argument is in every way parallel to the original. So it either shows that dualism is false or it shows that there is the very same problem with the original zombie argument. The problem here is that we have just assumed that qualitative properties are not nonphysical properties which seems unfair to the dualist. This is, of course, the precise complaint that the physicalist makes about the traditional zombie argument.

1.2. Shombies

A shombie is a creature that is micro-physically identical to me, has conscious experience, and is completely physical.[6] Shombie pain is just as painful as my pain is and shombie orgasms are every bit as pleasurable as mine are. My shombie twin and I all have the same experiences. The only difference, if it is a difference, is that shombie pain is completely physical. That doesn’t make it in the any different from the inside. What is like for me to have a pain and what it is like for my shombie twin to have a pain are identical in all respects. We have stipulated that shombie pain is just like my pain in every respect (qualitatively) and that my shombie twin is a complete micro-physical duplicate of me and that this is all there is to a shombie. The shombie is NOT a zombie. A zombie lacks phenomenal consciousness; a shombie doesn’t. The qualitative does, therefore, logically supervene on the physical and dualism is false. Zombies are metaphysically impossible.

We can formalize the shombie argument as below; where P is a complete physical description which includes a ‘that’s all’ phrase.

1. P and Q is conceivable

2. If (P & Q) is conceivable, then (P & Q) is possible

3. If (P & Q) is possible then dualism is false

4. Therefore dualism is false

(4) follows because in order for dualism to be true there has to be a zombie world but shombies show that there is no zombie world since the world physically identical to ours also has consciousness just like ours.

Again we see that this argument is exactly parallel to the original zombie argument. And again what this demonstrates is that either dualism is false or that the original zombie argument makes the same mistake that this one does. The mistake here is the same as before. We have simply assumed that qualitative properties are physical properties, which begs the question against the dualist.

1.3. Maria

Maria is Mary’s twin sister who was separated from her at birth and so is the intellectual equivalent of her super-scientist sister. However the evil scientists who raised Maria raised her as a super phenomenologist. She was raised in a special room where she was taught from a very early age to focus on her own experience. She learns to master all of the platitudes of folk psychology and so is a master of such things as that red is more like pink than it is blue and that turquoise is more like blue than it is like red and on and on to a degree that we can only dream of. Maria is able to discriminate between shades of color that we cannot (though perhaps we could with the proper training) also she is able to describe her experience as accurately as humanly possible. She, in short, knows everything there is to know about her own experience. She is, however, kept completely ignorant about all physical theories of our time are anyone else’s. She knows that she has a body but does not know anything about the way it works.

Then one day Maria is taught the completed science of her day. This includes everything from Aristotle’s theories to the completed physics of her time. She comes to know everything there is to know about the brain and color processing in the brain as well as the physical theory about light and the way it is reflected all the way down to the completed microphysics.[7] I have the intuition that Maria will then learn that her visual experience of red is just a brain state, just as she learns that water is H2O. She will learn that her color experience is a physical event in her brain. Maria will learn something that she would express by saying ‘oh, so that’s what my color experience is!’ Once she sees the identities she will be in a position to deduce the qualitative facts from the physical facts a priori.

We can reformulate the Reverse-Knowledge argument as follows,

1. ‘P àQ’ is a priori (the reverse-Knowledge intuition)

2. If ‘P àQ’ is a priori, it is necessary

3. If it is necessary, dualism is false

4. Dualism is false

This way of formulating it puts it in reverse-form to the way that Chalmers formulates the original knowledge argument. This argument is to me very compelling. In fact I suspect it describes the way that most physicalists come to be convinced of physicalism. And as with the previous two arguments what it shows is that either dualism is false or that it makes the very same mistake that this one does. The mistake here is just the assumption that the qualitative facts are a special subset of the physical facts just as in the original knowledge argument the assumption is just that they aren’t.

1.4. Mark

Mark is the name given by Yujin Nagasawa (Nagasawa XXXX) to Churchland’s (Churchland XXXX) Mary-like super-scientist who learns the completed nonphysical science without seeing red. When Mark is let out of his special black and white room and sees his first red ripe tomato there is no reason to think that he won’t learn what it is like to see red in exactly the same way that Mary did. This argument exactly parallels Jackson’s (Jackson XXXX) original formulation of the knowledge argument. Mark knows all of the nonphysical facts but yet learns something new when he sees red for the first time, therefore phenomenal facts cannot be deduced from the nonphysical facts. Whatever response the dualist gives to Mark can be given to Mary.

2. Type-C Physicalism

It will be useful for us to remind ourselves of David Chalmers’ (Chalmers XXXX) well-known classification of physicalist theories in terms of how they respond to the a priori arguments against it.[8] As we have seen the a priori arguments for and against physicalismt have a common structure. They start with a conceivability claim move to a possibility claim and then make a metaphysical conclusion. Type-A physicalists deny the conceivability claim. They deny that zombies are conceivable and insist that the zombie world is a world where there is consciousness. Typical type-A physicalists include Dan Dennett and Paul Churchland and often claim that it is analytically true that pain is a functional state. Chalmers, in fact, seems to equate type–A physicalism with being an eliminative materialist.

Type-B physicalists deny the possibility claim. They take the intuitive conceivability of zombies and Mary to be compelling but deny the zombies are therefore possible. They typically invoke Kripke’s notion of a posteriori identities. So take our empirical discovery that water is in fact H2O. We know that water equals H2O and that this identity is necessary (since all of them are). But still it is conceivable that water is not H2O in the sense that we can imagine a world where the watery stuff is not H2O; this is our old friend Twin Earth. On Twin Earth the stuff that falls from the skies, and which life depends on, and which people bathe in, etc is not H2O. It is some other stuff with a very complicated chemical formula we can abbreviate by XYZ. So the Twin Earth world is conceivable but not possible. I must admit the Kripkean picture influences me and I do think that the zombie and Mary intuitions are prima facie plausible.

The type-C physicalist admits that zombies seem conceivable but then denies that they are ideally conceivable. At the ideal limit we will be able to make the required deductions and we will see that zombies are not ideally conceivable. Type-C physicalism is clearly the most plausible kind of physicalism. It allows us to agree with the dualist that the anti-physicalist thought experiments are intuitively compelling, given what we know now, and also admit the intuitive principle that an ideally rational agent who knew all of the physical facts would be in a position to determine which things were contradictory and which things weren’t. Given the traditional rationalist assumption that contradiction is a guide to what is knowable a priori this agent would be in a position to know, a priori, all of the truths. The type-B physicalist denies this.

We can see that there are corresponding types of dualism. The type-A dualist will deny the conceivability claim in the reverse-thought experiments. The type-B dualists will admit that both are conceivable and then deny that they are both possible. The type-C dualist will hold that they both are prima facie conceivable but that only one of them is ideally conceivable. Chalmers at times has talked like a type-A dualist (Chalmers XXXX), which is partially what inspires the physicalist’s reaction that he is simply refusing to take physicalism seriously. Type-A dualism is plausible only if one assumes a kind of analytic dualism on which our concepts of qualitative properties explicitly noted that they were nonphysical. But stipulating that qualitative properties are nonphysical is question begging. And this is the heart of the matter. What non question-begging reason can one give to show that zombies are really conceivable and zombies and shombies aren’t? But he has also talked like a type-C dualist (Chalmers XXXX). Once we have set aside stipulative answers to the problem of consciousness and as long as we refuse to give up the thesis that conceivability in some sense entails possibility then type-C dualism is the only viable alternative. Since there are no a priori reasons to choose between type-C physicalism and type-C dualism only empirical discoveries will decide the issue. Thus the way that we will come to know whether physicslism is true or false will be a posteriori even though it can be known a priori.

3. Objections and Replies

3.1. To Type-C Physicalism

The main argument against type-C physicalism is that it threatens to collapse into either type-A or type-B physicalism and then will have all of the problems associated with those positions. But the kind of type-C physicalism advanced here does not fall to any of these objections. Let us take them in turn.

The argument against type-A physicalism is just that they have failed to take consciousness seriously. Consciousness cannot be eliminated or explained away. It is a real phenomena that is perhaps the one thing we know best about the world and there are no conceptual connections between physical and phenomenal concepts. So I am with Chalmers in setting aside analytic functionalism and all other eliminative views about conscious mental states. According to the kind of physicalism I am arguing for what allows us to complete the deduction of phenomenal facts from the physical facts is the a posteriori discovery of identities between phenomenal and physical properties. It is because of these a posteriori identities that we are able to deduce the mental facts from the physical facts. This is the position usually associated with type-B physicalism and so one may think that I fall to the other horn of the dilemma but that is not the case.

Chalmers has developed further arguments against type-B physicalism in quite a bit more detail and invokes his two-dimensional semantics. Chalmers argues that there is clearly a sense in which ‘water is not H2O’ is primarily ideally conceivable and so metaphysically possible. It is conceivable in the sense that if Twin Earth had turned out to be actual it would have been the case that water was not H2O. If Twin Earth were actual, as opposed to counter-factual, then water would have been XYZ. Whether we call the watery-stuff on Twin Earth, which would have been water if Twin Earth were actual, ‘water’ or not is irrelevant. When we are imagining Twin Earth we really do have access to some possible situation and if that possible situation had been actual then it would have been true that water was not H2O. This invokes the distinction between primary and secondary conceivability and the corresponding kind of intentions. The primary intention of a sentence gives us the truth-value for that sentence in possible worlds that we consider as actual. Thus, if twin Earth were actual water would be XYZ, and so ‘water is not H2O’ is primarily conceivable. The simple way to think about primary intensions is that they are descriptions that pick out different referents in different possible worlds (‘water’ has the primary intension ‘the watery stuff’ for instance). The secondary intention of a sentence gives us of the truth-value of that sentence at possible worlds considered as countered-factual. In other words we hold the actual world fixed and then ask what could be true of it. So, ‘water is not H2O’ is not secondarily conceivable since its secondary intention is false. There are no worlds where H2O is not H2O and given that water is actually H2O it is impossible for water not to be H2O.

Chalmers then argues that if we are careful to start with ideal primary conceivability then the zombie argument goes through. If the zombie world had been actual it would be the case that physicalism is false. This gets us to the claim that the zombie world is primarily possible, and Chalmers argues that this is enough to falsify physicalism. Therefore physicalists who endorses a posteriori identities between qualitative states and brain states cannot avoid the zombie argument by invoking Kripke. The dualist is in some sense conceiving a real primary possibility when they imagine a zombie world (just like the person conceiving Twin Earth is conceiving something which is metaphysically possible). Whether we apply our word ‘consciousness’ to it is irrelevant. The realm of possibilities has not shrunk and ideal primary conceivability is still a good guide to what is metaphysically possible.

But what the reverse-thought experiments show is that it is not clear that zombies really are primarily ideally conceivable. Zoombies and shombies seem to me to be just as primarily ideally conceivable as zombies; which is to say that they only seem contradictory when one has tacitly accepted a theory about what qualitative properties are but doing so begs the question against physicalism from the beginning. Chalmers starts with the assumption that zombies or the Mary intuition is in fact ideally and primarily conceivable. But it isn’t obvious that it is, at least it isn’t until one has shown what is wrong with the reverse-thought experiments and why they aren’t primarily ideally conceivable. I can even grant that the zombie world might be negatively conceivable in the sense that there is no obvious contradiction in imagining the zombie scenario to be true –just as Chalmers grants this for physicalism— but it is not positively conceivable. To be positively conceivable is to do more than merely be unable to detect a contradiction. We may simply not know enough to see that there is a contradiction. It is to actively envision the scenario holding in detail. So to positively conceive of the zombie world is to succeed in imagining a world that is physically identical to ours and which lacks qualitative consciousness.

But this cannot work since we do not yet know if physicalism is in fact true. If the identity theory is true then there is a contradiction in the specification of the zombie world for it asks us to imagine a world where a certain physical property is present and also not present at the same time; after all if the two properties are really the same property then wherever there is the one there must be the other. So if the identity theory is true zombies are not really ideally conceivable and so cannot yet be evidence against physicalism or used an argument that tries to show that physicalism is false. Just as in the shombie case. If dualism is true then there is a contradiction in the shombie world since it would have to both have phenomenal conscious (since it is described that way) and yet lack it (since there are no nonphysical properties). Someone must be begging the question here, but both sets of arguments are exactly parallel so there is no good a priori reason to say who is doing the begging. So Chalmer’s standard objection to type-B physicalism doesn’t apply to me. This is because unlike the thype-B physicalist I do not think that zombies are ideally conceivable.

One other objection to type-B physicalism comes from strong necessities. 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 be in pain). In short the idea is that 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 (‘the watery-stuff=H2O’ 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). Chalmers takes this to show that the postulated mind-brain identities do not behave like Kripkean posteriori necessities.

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 in the actual world? Chalmers, and Kripke, seem to think that it is a priori that the answer is no but there is empirical evidence that suggests that it is at least not contradictory to think that the answer is yes. In particular cases of Dental Fear shows 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.

David Rosenthal discusses dental fear in his (XXXX). Here is what he says,

Dental patients occasionally report pain when physiological factors make it clear that no pain could occur. The usual explanation is that fear and the non-painful sensation of vibration cause the patient to confabulate pain. When the patient learns this explanation, what it’s like for the patient no longer involves anything painful. But the patient’s memory of what it was like before learning the explanation remains unchanged. Even when what it’s like results from confabulation, it may be no less vivid and convincing than a non-confabulatory case.

Now, I have always felt that this dental fear stuff was a really convincing way of showing that there really is a reality/appearance distinction for pains, but when I have tried to research this I have not been able to find very much on it (and Rosenthal offers no citations), but it does seem to be a relatively common phenomenon.

Here is an excerpt from a paper on dental fear in children that tells a dentists how to deal with this

Problems that a dentist is convinced are associated with misinterpretation of pain may be addressed by explaining the gate theory of pain. A very basic explanation which is suitable for children as young as five is as follows. ‘You have lots of different types of telephone wires called nerves going from your mouth to your brain (touch appropriate body parts). Some of them carry “ouch!” messages and the others carry messages about touch (demonstrate) and hot and cold. The sleeping potion stops the ouch messages being sent, but not the touch and the hot and cold messages. So you will still know that I am touching the tooth and you will still feel the cold of the water. Your brain looks out for messages all the time. If you are convinced that it will hurt, it will. This is because if I make the ouch nerves go off to sleep and I touch you, a touch message gets sent. But your brain is looking for ouch messages and it says to itself, ‘There’s a message coming. It must be an ouch message.’ So you go ‘ouch’ and it hurts, but all I did was to touch you. It’s just that your brain was confused.’ (The language may, of course, be adjusted for older children.) If this fails to work, then active treatment should be stopped. (from Dental Fear in Children)

This is clearly fool’s pain, as evidenced by the fact that the way they treat it is not with more medication, but with an explanation, pitched at the kids level, of why what they are feeling is not pain. So it is possible to be in the epistemic position of someone in pain and yet not be in pain. When we conceive of pain that isn’t c-fiber firing we may be conceiving of someone in a dental fear-like position. This person picks out some state in the same way that we normally pick out c-fiber firing, that is, as painful, even though the state they pick out is not c-fiber firing. Just as in the water/H2O case.

But could it be the case that the painfulness of pain and the sensation of pain are contingently related? If this were the case it would have to be the case that the very sensation of pain that I now have could have existed and failed to be painful for the creature that had it. Is this possible? Yes. There is evidence from what is known as pain asymbolia (Grahek 2001). Pain asymbolics have a specific kind of brain damage which leaves them able to feel pain but not as something unpleasant. They are able to discriminate painful stimuli, saying for instance that something hurts and that it is a burning pain, or a pinching pain. They are also able to reliably judge how intense the stimulus is. Yet they fail to be motivated to withdraw and say that they do not find the sensation unpleasant at all. They often laugh at the pain. They seem to know that pain is supposed to be this horrible thing that we want to avoid at all costs, but when the pain actually comes it is a pathetic joke. Our intuitions that pain and painfulness cannot come apart thus turn out to be wrong.

Something that Kripke says in another context is useful here. He says,

The fact the we identify light in a certain way seems to be crucial, even though it is not necessary; the intimate connection may create the illusion of necessity. (p 139)

He is here responding to the objection that a world where something besides photons, say heat, was the cause of visual experiences (rather than photons) would not be a world where light was heat. So also it seems that being unpleasant is crucial to the way we identify being a pain. But this crucial connection generates an illusion of necessity. The fact that pain is painful for us is a contingent feature of the sensation of pain, as evidenced by pain asymbolia. The state we pick out via this contingent property, the sensation of pain, cannot be other than it is. If it turns out to be identical to a brain state then pain will be a brain state in all possible worlds. When we think that we are conceiving of pain existing without the brain state we are really imagining that there were a creature who was in the same epistemic situation as we are when we are in pain but is mistaken. We thus imagine someone who is in the situation of the dental fear patient. This person thinks they are in pain when they are not. But can we conceive that the pain was not physical? No. If physicalism is true then pain is essentially physical and only contingently unpleasant. To conceive of pain as being non-physical is as impossible as conceiving that H2O were non-physical. The illusion of contingency is thus explained away in the very same way as all the others. What is contingent is that pain should be unpleasant to us.

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. Just as Twin Earth offer no threat to the identity of water and H2O. What needs to be shown to threaten physicalism is that there is a possible world which is a microphysical duplicate of the actual world and 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 microphysical duplicate of ours, say with different laws of physics, 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 microphysically 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 microphysically 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 microphysically 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.

One may think that this ignores Chalmers’ appeal to primary conceivability and focuses on secondary conceivability.[9] 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. The traditional type-B physicalist agrees, at least tacitly, that whatever ‘the painful-stuff’ picks out here will be identical to what it picks out in all modal contexts but it is not obvious that this is the case. This opens up the space for the kind of view I am defending. One can hold that ‘the painful=c-fiber firing’ behaves exactly like ‘the watery-stuff is H2O’ and so disputes that .

I conclude that the present view neither collapses into type-A or Type-B physicalism and so is not threatened by any of the objections to those positions. Let us now turn to addressing objections specifically to the reverse-thought experiments.

3.2. To the Zoombie Argument

The zoombie intuition relies on there being nothing contradictory in the totality of the nonphysical properties not including phenomenal properties. Though as formulated it is valid one might argue that it is unsound.[10] One might, for instance, think that this is so because nonphysical properties, though necessary for qualitative consciousness (according to the dualist), need not be sufficient. That is, there might be a creature that was identical to me in all nonphysical respects (that is, had all of the nonphysical properties that I in fact do) but because it lacked a certain physical element these nonphysical properties were ‘inert’ and so the creature does not have any conscious experience (a special kind of neuron or a certain kind of firing pattern, might be needed in order to ‘turn on’ the nonphysical properties in such a way as to get consciousness). If this is possible then the existence of zoombies does not show that dualism is false.[11]

But there cannot be inert nonphysical properties in the zoombie world as properly conceived. The zoombie world is one nonphysically exactly like our world. So if the dualist thinks that they need certain physical properties, or certain laws of physics, in order for me to consciously experience, say, pain, then that will be present in the zoombie world.[12] If there were nonphysical qualitative properties in the zoombie world they would result in conscious experience. This is because the zoombie world is stipulated to contain exactly the same nonphysical properties that I actually have and to contain them in exactly the same way that they are actually contained. This is not to deny that worlds like the one in the objection are possible; they may be, but these worlds are not the zoombie worlds. Compare: the physicalist like myself admits that there are physical worlds where there is no consciousness but these worlds are not physical duplicates of our world and so are not truly zombie worlds. In fact the physicalist like me thinks that it is one these worlds that the dualist actually succeeds in conceiving.

Some philosophers argue that the zoombie argument is not really a parody of the zombie argument. If this is so then one can argue that the zombie argument is indeed a bad argument but the flaws it has do not infect the traditional zombie argumtn.[13] The basic reason for this is that there is an alleged important dis-analogy between the original zombie argument and the zoombie argument. This alleged dis-analogy resides in the fact that no self-respecting dualist can accept NP as a complete list of the nonphysical properties. This is because the dualist will insist that a complete list of the nonphysical properties that I in fact have will explicitly include qualitative properties. NP is thus contentious as it already assumes that dualism is false, they allege, and so the zoombie argument really does beg the question against the dualist. On the other hand all the parties to the zombie debate, this objection proceeds, agree on the physical description specified in P and so the traditional zombie argument does not beg the question in the way that the zombie argument does.

Suppose for a second that we grant that there is this difference between the zombie and zombie arguments does it then follow that the traditional zombie argument is not a bad argument? It is not obvious that it does. The dualist can presumably make sense of whatever way we fill out NP though they will not think that it is ideally conceivable. That is, the issue here is of the conceivability of NP & ~Q. I can’t see any reason to think that it isn’t conceivable unless you already think that qualitative properties are in fact nonphysical. Compare the property of being a table or of being water. Chalmers thinks that water facts are deducible a priori from a complete microphysical description of the actual world so someone who claimed to be able to conceive of all of the physical facts (and so there being H2O just like there is here) without water facts would be mistaken. He can grasp what the opponent seems to be conceiving when they say ‘P & ~W’ is conceivable but he denies that it is actually conceivable because it contains a contradiction. So too in the zoombie case.

But is it right that the zoombie argument begs the question in a way that the zombie argument doesn’t? The basic objection was that the way the zoombie argument is set up rules out dualism from the beginning and so is unfair to the dualist. It is true that the dualist allows the physicalist to fill in the placeholder description in P with whatever theory of physics they want but the problem lies not with P but with Q. The upshot of the discussion about dental fear and pain asymbolia was 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 placeholder ‘~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 one cannot then rule out that the Q which are lacking from the zombie world are the same qualitative properties we have here. The dualist may be conceiving of a world physically identical to ours and which lack a different kind of qualitative property than the one we have around here. This does not threaten physicalism since this world does not lack the kind of qualitative properties that the actual world has. So to get the zombie argument off the ground you must assume a semantics for the terms in Q, just as to get the zoombie argument off the ground you have to assume a semantics for NP. This may be more obvious in the zoombie case but it was designed to highlight the flaw.

3.3. To the Shombie Argument

Shombies are creatures that are physically identical to me and which have consciousness and lack all nonphysical properties. One objection to shombies might be that it amountes to no more than asserting “it is conceivable that physicalism is true, physicalism is a modal thesis and if true at any world physically just like ours it is true at all possible worlds that are physically just like ours, therefore since it is true at one possible world it is true of our world”.[14] This way of putting it makes the shombie argument sound like a version of the ontological argument as advanced by people like Plantinga. But this kind of argument isn’t very interesting, one might think, because it is not as though we have found something from which the truth of physicalism follows. We’ve simply insisted that it is true. One thing to note before we address this is the fact that this is exactly what is going on in the traditional zombie argument. When one asserts that zombies are conceivable one asserts “it is conceivable that physicalism is false. Physicalism is a modal thesis and so if true would be true at all possible worlds physically just like ours. Since there is one world where physicalism is false it is false of our world”.

But even if one is not moved by this there is a response that adapts a strategy that Chalmers uses in response to Yablo’s meta-modal argument against CP. Chalmers argued that what he was doing was merely conceiving of one particular possible world and not the entire space of possibilities. In fact he argues that our intuitions about modality become less trustworthy when we try to make meta-modal claims about the entire space of possibilities. So too, I merely conceiving of one possible world. When we conceive of the shombie world we only conceive of a world physically and qualitatively just like ours but which is completely physical in nature. We are not making meta-modal claims about the space of possibilities. True, physicalism is the modal thesis and so if true at one world it follows that it is true for all physically identical world, but I don’t need to conceive of the shombie world that way. All that I need to do is to conceive of the shombie world is being physically identical to our world as having a creature there who has conscious experience in exactly the same way that I in fact do. This is not to conceive of physicalism being true and so not to employ the argument of strategy criticized above. This is because the shombie argument is only designed to show that dualism is false, not that physicalism is true. For dualism to be true there must be a world that is physically identical to ours which lacks qualitative consciousness. Shombie show that there is no such world since the world that is physically identical to ours is a world of conscious experience. So just the conceivability of one possible world is in question and that is enough to show that dualism is false. The modal aspect of physicalism comes from independent considerations about the necessity of identities.

3.4. To the Reverse-Knowledge arguments

We see many of the same objections with the reverse-knowledge arguments. For instance one might think that the argument based on Maria is question begging in the sense that it is a one-premise argument. Something like Maria learns that dualism is false, therefore dualism is false. The original Mary argument doesn’t do this because, one may think, it only claims that Mary learns something or other about red and given her circumstance this is supposed to entail that physicalism is false.[15] But this is not exactly fair. The dualist thinks that Mary learns a lot about red when she gets out of her black and white room. She will learn how the nonphysical color properties, say, correlate with the physical properties of the brain for instance. So the original Mary does depend on Mary learning one particular thing, she learns that there is more to color perception than physical properties. So, both of the arguments beg the question this way. This is, of course, the point I’m trying to make! The Mary argument depends on our having a certain intuition that learning what it is like to see red would be truly learning something unaccounted for by the physical facts. So too in the Maria case I have the intuition that Maria will learn that there is nothing more to consciousness than the physical. In this sense the two arguments are on a par. Mary learns that there is more to reality than the physical. Maria learns that there is nothing more to reality than the physical.

So, the reverse knowledge argument from Maria shows that qualitative facts are conceivably deducible from a completed physics. That is, Maria having only phenomenal concepts and then introduced the completed physical theory will be able to tell a priori when phenomenal concepts apply in other cases. One may also object to the notion that Maria’s deduction is a priori. After all, she is able to do so only because she has had the relevant phenomenal experience. But this is no objection, at least not for the dualist like Chalmers and Jackson who have argued empirical knowledge as long as it plays only a causal role (for example that needed for concept acquisition) is no bar to a priori knowledge. According to them as long as the concept only facilitates the deduction and does not justify the deduction will still count is a priori. So Maria needs to have the experience in order to acquire the phenomenal concepts but once she has those and the completed physics the deduction will be a priori since she will not need to use those concepts to justify any step in the deduction. She will instead use the identities that she learned a posterirori.

Chalmers briefly mentions a strategy like this in his “phenomenal concepts and the knowledge argument” calling it “one of the more powerful replies available to the materialist.” He there lists several prima facie objections to this strategy. His first objection is to fall back on the zombie intuition. But we have as we have seen this doesn’t help. Secondly he wonders whether someone like Maria will be able to deduce that other creatures, like bats and Martians, have phenomenal experience. But there is no non-question begging reason to think that Maria will not be able to do this. The same is true for his third response along the lines that Mary might have a concept like phenomenally indistinguishable and yet be unable to tell if two people were having the same qualitative experience.

Finally he objects that someone like Maria will have to crucially rely on introspection in order to complete the deduction. And since introspection yields a posteriori knowledge the deduction will not be a priori. First it is not clear why she would need to rely on introspection in this way. Once the relevant concept is acquired the deduction goes through just as in the water H2O case. At least, there is no a priori reason to think otherwise.

Let us finally, then, address Mark. Nagasawa argues that this argument is successful against any kind of reductive dualism, whether property or substance. A reductive dualist holds that qualitative facts can be reduced to or deduced from a set of nonphysical facts, like the protophenomenal facts that Chalmers mentions in his panprotopsychism (Chalmers XXXX). The argument, however, is not successful against a non-reductive version of dualism. The non-reductive dualist claims that qualitative properties cannot be reduced to any other kind of property whether protophenomenal or not. The knowledge argument against dualism, according to Nagasawa, shows that non-reductive dualism is the only viable option for someone who wants to use the knowledge argument against physicalism. One could then reason that Mary merely shows that a reductive version of physicalism isn’t viable but that a non-reductive physicalism is (like a Davidsonian Anomalous Monism perhaps).

On the other hand one might think that Mark shows that a dualistic theory that does not hold that the phenomenal concepts must be experienced in order to be fully apprehended is just as doomed as a physicalism that does not hold this. The two theories are on an a priori equivalency here. I suspect that a dualist like Chalmers will argue that once Mark sees red he will be able to deduce, a priori, the qualitative facts from the nonphysical facts and this is the way that my intuitions lie with physicalism. Thus the traditional and reverse-knowledge arguments together suggest that with the concepts we can male the deductions and that without them we are unable to make the deductions. But just because we must actually see red in order to fully acquire the concept of phenomenal red is no objection to physicalism.[16] Dualism is committed to the same thing. The dualist and the physicalist agree that phenomenal concepts are the kinds of things which depend on our having had the relevant experience. And if physicalism is true then all that means is that the property that we must have in order to have a full concept of it is an interesting physical property; this by itself cannot be an objection unless one has just assumed that these kinds of properties are not ultimately entirely physical.

4. Conclusion

So as we have seen the use of a priori methods to determine whether physicalism is false simply fail to do anything except to tell us where sympathies lie. What theories pne accepts, either tacitly or not, as true influences what one finds to be conceivable. This is the only way that we can explain why it is that some people find zombies conceivable while others find zoombies conceivable that is consistent with our desire to maintain a link between conceivability and possibility. One the parity arguments are on the table there is nothing short of table pounding that can decide which one is really ideally conceivable and which one is merely prima facie conceivable. In order to answer that question we first need to know is whether physicalism is true or false. Only once we know whether physicalism is actually true or false will a priori methods yield anything useful;[17] but of course by then we won’t need them!