The last three weeks have been extremely hectic for me. Starting with the Long Island Philosophical Society meeting (which was at LaGuardia and which I helped organize), and then the Pacific apa, and then when I got back the Felician Ethics conference (more about that later)…not to mention a pile of papers to grade and the search we are doing at LaGuardia…very busy indeed. Well things are starting to settle down a bit now and I wanted to reflect on what happened.
My talk went well. There was lively and helpful discussion. My commentator was Robert J. Howell from Southern Methodist University (coincidently the same commentator from Consciousness Online. A video of his comments is available there is anyone is interested). Robert brought up two interesting objections that I wanted to discuss.
The first was to the zoombie argument. A zoombie, you might recall, is a creature that is identical to me in every non-physical respect and which lacks non-physical qualitative consciousness. Robert argued that the zoombie argument was invalid since non-physical properties are necessary for qualitative consciousness (according to the dualist) but they need not be sufficient. That is, there might be a creature that was identical to me in all non-physical respects (that is, had all of the non-physical properties that I in fact do) but because it lacked a certain physical element these non-physical properties were ‘inert’ and so the creature did not have any conscious experience(a special kind of neuron, or a certain kind of firing by a neuron might be needed in order to ‘turn on’ the non-physical properties in such a way as to get consciousness experience of pain). If this is possible then the existence of zoombies does not show that dualism is false(what is nice about this is that this is exactly the same kind of move that a physicalist like me makes about the zombie world. What you are actually conceiving, and what is actually possible is a world that looks like ours but in not micro-physically identical to it. The exact parity between these two arguments is again striking).
I argued that for a creature to really be a non-physical duplicate it may be the case that it has to also be a physical duplicate. So if the dualist thinks that I 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. So there cannot be inert non-physical properties in the zoombie world. If there were non-physical qualitative properties in the zoombie world they world they would result in conscious experience. This is not to deny that worlds like the one that Robert is suggesting 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 zombie worlds). The basic point is that the zoombie world is one exactly like our world; it has all of the same physical properties and all of the same laws and all of the same non-physical properties, but no non-physical qualitative properties. That world is conceivable and that world is the one that shows that property dualism is false.
Robert’s response was that if I allowed the dualist to claim that we needed to have complete micro-physical duplication in order to get non-physical consciousness experience (as opposed to merely ‘inert’ non-physical qualitative properties) then it looks like I am admitting that the traditional zombie world is conceivable since I hold that the zoombie world will now have to be a micro-physical duplicate of our world and also that the zoombie world lacks qualitative cosnciousness. But then zoombies are a kind of zombie! true zoombies are allowed to have non-physical properties (though not non-physical qualitative properties) so they may not be exactly like traditional zombies, but they are sufficiently alike to falsify my argument that zombies are inconceivable.
But I don’t need to claim that the zoombie world lacks qualitative consciousness entirely. All that I need is for the zoombie world to lack non-physical qualitative consciousness. So, since we are now allowing that zoombies must be complete physical duplicates of me then they must, according to me, have physicalist consciousness. So this move that Robert is suggesting just again points out the stalemate that is inevitably reached when one tries to resolve empirical issues with a priori methods. If physicalism is true then the modified zoombies will have consciousness of a physical kind, where as if dualism is true then, according to them, these modified zoombies will have non-physical consciousness. If we knew how the actual world was then we would be in a position to tell a priori (in Chalmers’ sense) which of these is correct. But now all we can tell a priori is that given one thing something else follows. This is exactly the position we are in with respect to things like Goldbach’s conjecture. If Goldbach’s conjecture is true then every even number greater than 2 can be expressed as the sum of two prime numbers if it is false then it is not the case that every even number greater than two can be expressed as the sum of two prime numbers. From our point of view now it seems conceivable that it could go either way. But given standard assumptions about mathematics it cannot really go either way. If it is true, then it is necessarily true. We cannot at present tell which it is. The same is true with respect to the dualism/physicalism debate. A priori methods are useless to us given the epistemic position we are in. I grant that as we approach the ideal limit of we things which are not a priori now will become so, but that does us no good right now. The only way we can advance debates about the nature of consciousness, from where we are now, is by a posteriori empirical investigation.
The second objection that Robert raised (and which I haven’t addressed in my response over at Consciousness Online) is aimed at the Shombie argument. Shombies are creatures that are physically identical to me and which have consciousness and lack all non-physical properties. Shombies have received more attention than zoombies (in fact at the apa Katilan Balog advanced an argument of this type. Robert’s objection to Shombies was that it amounted to no more than the following “it is conceivable that physicalism is true, physicalism is a modal thesis and if true at any world is true at all possible worlds, therefore since it is true at one possible world it is true of our world”. 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, Robert continued, because it is not as though we have found something from which the truth of physicalism follows. We have simply insisted that it is true.
Now in my response I complain that this is exactly what is going on in the traditional zombie argument, but later in conversation I tried to adapt the strategy that Chalmers uses in response to Yablo 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. So too, I am merely conceiving of one possible world and not making meta-modal claims about the space of possibilities. true, physicalism is a modal thesis and so if it is true at one world it follows that it is true for all physically identical worlds, but I don’t need to conceive of the shombie world in that way. All that I need to do is to conceive of the shombie world as being physically identical to our world and as having a creatures there who have 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 argumentative strategy that Robert criticizes. 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 lack qualitative consciousness. Shombies show that there is no such world since the world that is physically identical to ours is a world with conscious experience. So just the conceivability of one possible world is in question and that is enough to show that dualism is false.
Towards the end of the discussion David Pitt made a plea for agnosticism. Nobody knows what is going on here, so there is no more reason to prefer physicalism as there is to prefer dualism. This is an empirical matter and we are not in a position to really say which is true. But my argument was that there is no a priori reason to prefer one theory over the other. There are a posteriori reasons to prefer physicalism over dualism. A meta-induction over the history of science seems to me to clearly show that appeal to non-physical properties are superfluous. Every time we posit something like this it is explained away 1000 years later. We also, as Robert pointed out, have good a posteriori reason to accept causal closure of the physical and good reason to think that mental properties are causally efficacious, and therefore good a posteriori reason to think that mental properties are physical. So all in all physicalism seems to me to have the upper hand. But I agree with David that we are not in a position to say for sure what is going on with the mind. However, the failure of a priori arguments against it and the a posteriori arguments in favor of it make it reasonable to think that it is a live possibility. In fact, given the utter mysteriousness of non-physical properties there is strong presumptive evidence against dualism and for physicalism. This is what my view has in common with Perry’s antecedent physicalism. We should assume that physicalism is true unless we have good reason to think otherwise. We don’t, as of yet, have good reason to think otherwise and so we should assume that it is true.
Torin Alter made several good comments, but I can’t recall all of them. Since I had been claiming that whether physicalism was true was an a posteriori empirical matter he asked me if I thought there was some experiment that we could do which would show that dualism was true or that physicalism was false. I don’t think that there is. What I think is that as we approach the ideal limit if scientific investigation we will either start to see that we can make deductions from physical states to qualitative states in the way that the physicalist thinks or that we will not be able to do this. So it is not as though one experiemtn will vindicate physicalism or falsify dualism. Rather it is that at the limit the deduction will be possible or they won’t. This is what will determine which view is ultimately true of our world. Now, it may be the case that we don’t need to get to the limit, but only sufficiently close to it to see how the deduction could be made (like the position that we are in right now with respect to table facts. Maybe we can’t actually make the deductions because of restriction on our computing power and lack of complete knowledge of physics but even so we can see that it could be done). He also pointed out a useful terminological point. He pointed out that I sometimes talk as though prima facie conceivability is an epistemic notion whereas ideal conceivability is a metaphysical notion but according to Chalmers both of these notions are purely epistemic notions. I think that the confusion follows from my trying to go back and forth between Chalmers’ terminology and Kripke’s terminology. I take it that the distinction between epistemic possibility and metaphysical possibility from Kripke maps onto the prima facie/ideal conceivability talk from Chalmers. Epistemically possible means that for all I know it may be possible, but it may not be possible. Metaphysically possible means that it is a ‘real’ possibility in the sense that there is a possible world corresponding to it. So it is epistemically possible that Goldbach’s conjecture is true, and it is epistemically possible that it is not. But both cannot be metaphysically possible. Thos who want to preserve the link between conceivability and possibility will, like me, think that contradictory epistemic possibilities both seem conceivable but both are not metaphysically possible. I take it that prima facie conceivability means ‘seems conceivable but on ideal reflection might not be’, whereas ideal conceivability means ‘conceivable on ideal reflection’ (ignoring primary/secondary and positive/negative distinctions). Am I wrong about this?
Michael Tooley wanted to know how I was characterizing the physical/non-physical distinction. He wanted to maintain (so it seemed to me) that a property was non-physical if in order to fully know about it one has to experience it from the first person. This seems wrong to me. I use ‘physical’ in the way that Chalmers uses it (I hope) as ‘property which figures in a completed micro-physics or can be deduced from such properties’. The second clause in that description of physical leaves open the possibility that qualitative properties have to be ‘had’ in order to fully understand them. It may be the case that one does not truly have the concept of blue unless one has actually seen blue. But this doesn’t mean that we couldn’t make deductions from physical properties to qualitative ones. We may need to have the experience in order to acquire the concept but once we have the concept we can make the requisite deductions. This is exactly the strategy that Chalmers and Jackson argue for in defense of the claim that physicalism should entail qualitative properties. We may need to acquire a concept of water from experience in order to make deductions from physical facts to water facts, but the deductions still count a a priori because the concept just enables the deduction it doesn’t play any justificatory role in the deduction. The same is true in this case. So if it is true that we need experience in order to fully have the concepts in question there is no reason to think that we shouldn’t be able to make the deductions in question. This is partly why the Knowledge argument is question begging. If Mary knows all of the physical facts about color and what it is like for Mary to see red is a physical fact (or can be deduced from a physical account) then she should know it in her room. To assume otherwise is to beg the questions against phsyicalsim. Robert seemed to agree with this line of argument and suggested that he is working on something similar that he calls ‘subjective physicalism’.
Ok this is getting ridiculously long, so I will stop now.