In the third chapter of his book The Conscious Mind, Chalmers provides five arguments supporting his claim that consciousness cannot be reductively explained. This paper will examine the first of those five arguments – the "zombie" argument – and show that Chalmers fails in guaranteeing the truth of his conclusion by overestimating the credibility his intuitions play in his argument. Instead of battling one set of intuitions (ours) against another (Chalmers’) – as often seems to be the case in contemporary arguments on consciousness – we will examine the intuitions to which Chalmers appeals and attempt to ascertain their credibility.

    What are zombies? The notion of a zombie is one of a thing that is functionally and psychologically identical to us, but not phenomenally aware. In other words, they are capable of walking around and doing exactly as we do, reacting in the same way to every stimulus and generally showing every sign of being exactly like us. The only difference is that a zombie is totally unconscious. There is nothing that it feels like to be a zombie; if you could somehow partake in the "mental life" of a zombie, you would experience no "redness" when looking at a rose, for example. It is traditionally granted, for the sake of the argument, that zombies are also physically identical to us – they have the same DNA, the same configuration of cells, the same neural pathways, etc. Zombies could provide you a description of the zesty taste of lemon sherbet, for example. They could paint a landscape in the style of the Impressionists. They could even tell you what it was like to be in love. Despite this, they would lack phenomenal awareness.

    The most important question for David Chalmers with respect to this issue is whether we can actually conceive of zombies. If we can conceive of such things, as Chalmers insists we can, then, says Chalmers, they are logically possible. "The question is not whether it is plausible that zombies could exist in our world, or even whether the notion of a zombie replica is a natural one," argues Chalmers (1996, p. 96); "the question is whether the notion of a zombie is conceptually coherent." Further, he argues that the logical possibility of zombies requires us to accept that we will be unable to explain consciousness reductively –wholly in terms of simpler or more basic entities – because it shows that there is no logically necessary connection between phenomenal consciousness and the physical world.

    Chalmers’ argument from The Conscious Mind can be spelled out more explicitly as follows:

1. We can conceive of zombies. (Premise)
2. Zombies are physically identical to us but lack our phenomenal experience. (Premise)
3. We can conceive of things that are physically identical to us but phenomenally barren. (1, 2)
4. Conceivability entails possibility. (Premise)
5. Things that are physically identical to us but phenomenally barren are possible. (3, 4)
6. One set of properties (b-properties) supervene logically on another set (a-properties) if no two logically possible situations are identical with respect to their a-properties but distinct with respect to their b-properties. (Premise)
7. Phenomenal facts do not logically supervene on physical facts. (5, 6)
8. A natural phenomenon is reductively explainable in terms of some low-level properties precisely when it is logically supervenient on those properties. (Premise)
9. Conscious experience is not reductively explainable in physical terms. (7, 8)

    Daniel Dennett has suggested (1995) that those who claim to be able to conceive of zombies sometimes fall far short. Their conceptions of zombies do not match the description given above; instead, they sneak in other differences – besides the accepted lack of phenomenal consciousness – making the notion more palatable. For example, they assume telltale behavioural differences, when this is explicitly ruled out by our definition. (Admittedly, these substitutions often happen with the best of intentions; the author does not usually notice them.) This revised notion of zombies, however, cannot be made to perform the duties expected of the original.

    Our first test, then, is to ask whether our intuitions are about relevant objects. Are we actually conceiving what we claim to be conceiving, or have we accidentally switched apples for oranges unwittingly? In the case of Chalmers, he does not seem to make any obvious errors in description or explanation that might lead us to believe that he has in mind a faulty conception of zombies. (We will look at this matter from a different direction later in the paper.)

    In his discussions of zombies, Chalmers suggests another test we can use to judge our intuitions. "Some may be led to deny the possibility [of zombies] in order to make some theory come out right," suggests Chalmers, "but the justification of such theories should ride on the question of possibility, rather than the other way around" (1996, p. 96). Basically, an intuition untainted by theory is far preferable to a post-theoretical intuition. To state this test more explicitly, we must ask ourselves whether we hold a certain intuition as the result of a theory we wish to defend, and if so, we should consider that intuition suspect. This is an excellent point in theory, but difficult to put into practice. This is because the theoretical framework through which we view the world tends to inform our intuitions in a significant way. If we accept gremlins into our ontology, for example, we may find that we can have quite strong intuitions regarding their presence and role in the world (what else could be responsible for the mechanical failures of my automobile when no other obvious cause is present?) regardless of how unjustified we are in holding our view. Concerning the zombie matter in particular: it seems difficult to tease apart our intuitions from our theoretical leanings, and so perhaps it would be advisable to set this test aside until such time as we are better able to separate one from the other.

    History has for us a cautionary tale regarding intuitions that we can perhaps use to formulate a third test by which to judge our intuitions. As human beings, we have traditionally attributed great importance to ourselves in the grand scheme, but our illusions of grandeur have been repeatedly disrupted by the discoveries of science. Many of the attributes or qualities that we have traditionally ascribed to ourselves to be indicative of our uniqueness have been shown, through the progress of scientific explanation, to be either limited in counter-intuitive ways or simply illusions. Examples are not hard to find; once the theory of an Earth-centred universe was discarded, we were removed from our privileged place in the universe. The theory of evolution argues that we shared an origin with all other living things, a view unacceptable to many precisely because it deprives us of our special position apart from all other life forms.

    Even other, more basic chauvinisms have not been immune to challenge; a perfect example would be that of intelligence. We are special because of our great intelligence, argue some, since our cognitive abilities far surpass anything else on this planet. Progress in computer technology, however, has humbled us in this respect. A simple chess program on your home computer can now play well enough to beat most people, most of the time (and some of us all of the time!). Our practice of science has served well to rid us of many of our chauvinisms, although often not without a fight. Perhaps the notion of phenomenal consciousness is born of a similar chauvinism, a remnant of our desire to find a privileged place for ourselves in the cosmos; we are rare instantiations of the mysterious phenomenal consciousness made even more rare because we need not even share it with our functionally equivalent zombie brethren. In general, then, we must ensure that our intuitions are not infused with baseless chauvinism before we can accept them wholeheartedly.

    Dennett – one of Chalmers biggest critics – does not make, at any point, such bald accusations against Chalmers or anyone else. It certainly seems, however, as though such thoughts figure in his responses to those who find reductive explanations of higher level features such as life or consciousness difficult to accept. "[W]e naturalists think that this elevation of consciousness is itself suspect, supported by tradition and nothing else," suggests Dennett (1999). While a valuable test to include in our arsenal, nothing that Chalmers has written shows any obvious signs of this chauvinism so let us clear him on this charge for now, as well. (We should remain vigilant, however, in case such biases should ever present themselves explicitly.)

    A fourth potential test – and perhaps the most important – of our intuitions is one of logical self-consistency. [does fourth line meet this condition] Before we proceed, however, it would be appropriate to discuss the fourth line of Chalmers’ argument, as it proves quite relevant. Chalmers suggests that our ability to conceive of some thing or state of affairs entails that whatever we are conceiving is logically possible. Recognising that this move may seem suspect to many, he has since defended it in an unpublished paper (still in first draft) entitled "Does Conceivability Entail Possibility?" (1999) that he has posted on his website. In this paper, he strives to explain in detail the various potential relationships between conceivability and possibility. His paper revolves around three dimensions of conceivability, namely: prima facie vs. ideal conceivability, primary vs. secondary conceivability, and positive vs. negative conceivability. Once he has established those distinctions, he then works out their implications regarding the validity of a move from each of the resulting composite notions of conceivability (e.g., primary positive ideal conceivability) to possibility. (All that is necessary for the argument that follows is an understanding of the prima facie / ideal conceivability distinction. The others do not play a role in this analysis and will thus be set aside.)

    After explaining these various dimensions of the term "conceivability", Chalmers points out that some kinds of conceivability provide stronger grounds for inferring logical possibility than others. Prima facie conceivability, for example, is a much poorer guide to possibility than ideal conceivability. Something that is prima facie conceivable could potentially be undermined by further reflection which uncovers a contradiction in or misdescription of the supposedly conceivable state of affairs, while no such concern exists for ideal conceivability.

    Near the end of his paper, Chalmers claims that zombies are ideally conceivable. One assumes that this derives from his belief that zombies are "obviously coherent" (1996, p. 96), since clearly any concept with logical coherence would be ideally conceivable. It does not seem, however, that we can simply grant this to Chalmers. I do not take the conceivability of zombies to be an obvious truth; if it were obviously true, then there would be much less conflict in this area then there actually is. Perhaps there is a strong a priori relationship – available to us once we had an adequate understanding of the terms involved – from the physical world to the phenomenal world and we have yet to realise it. If that were the case, then zombies would not actually be ideally conceivable at all. They would certainly be prima facie conceivable, but Chalmers grants that this would be inadequate to guarantee their logical possibility. He acknowledges the possibility of this response, but suggests that "in the zombie case, this materialist will concede that we have secunda facie positive conceivability, the sort of positive conceivability that is not undermined by a reasonable period of reflection; and we have seen that secunda facie conceivability is an extremely good guide to possibility" (1999). Even if we agree with Chalmers here, this is certainly a retreat to a weaker point than he had originally set out prove.

    Pressing on, Chalmers argues that case for the conceivability (and, hence, logical possibility) of zombies is bolstered by considerations regarding non-standard realisations of ourselves, such as Block’s Chinese Nation example (1980). After all, a functional equivalent is a functional equivalent, regardless of how radical the instantiation is; if we can accept the possibility that a radically instantiated functional equivalent of us could lack phenomenal awareness, then this should provide support to the notion of a zombie. Suppose that each person in China was provided with a radio and then instructed to emulate the behaviour of a single neuron, such that the overall system was organised in a causally equivalent way to the human brain. (If a billion people are insufficient, then suppose that China contained a trillion individuals.) This brain-equivalent could even be given control over a mechanical body equipped with sensors to give the brain-equivalent the appropriate sensory input. A great many people would find it difficult to accept that a unified consciousness could arise out of such a system. Chalmers, himself, rightly argues that the metaphysical possibility of such a system is irrelevant; all that is important to his case is that it is a coherent claim to say that such a system lacks conscious experience. How, then, shall we determine whether this is actually a coherent claim?

    This would seem to be an easy exercise since we are reasonably familiar with groups of individuals and in our experience they never exhibit an emergent "group consciousness". Expanding the group from a dozen – or a hundred, depending on the size of group that first came to mind – to a billion or more seems like a relatively straightforward matter. Our intuitions indicate that the larger group will be exactly what the smaller group was, only more so. A small, but loud group will get louder when people are added; the colour red will not "emerge" as a property of the group once it reaches a suitable critical membership limit. Following from this, since there was no consciousness emergent from the small group, we should expect the same from the large group.

    We must be careful, however, where we place the property we are trying to consider. If a group consciousness did result from our Chinese Nation experiment, it is very possible that none of the individual Chinese people involved would realise such a thing was happening. I maintain that one of the reasons our intuitions may be faulty on this matter is because of this misplacement of the property in question. Some might assume that as one of the members of the Chinese nation, that they would have access to this emergent consciousness. There would not necessarily be a "shared" consciousness that everyone would enjoy, in an immediate sense. Another example: even if the atoms that comprise a television were individually conscious it does not follow that they would necessarily be aware that they were involved in the shared function of being a TV. In fact, it is probably quite unlikely. If we remove consciousness from our examples, our grasp of extremely large organised structures can still be seen to be very limited; I doubt that many of us are capable of explaining the behaviour of a computer based on its atomic components, for example.

    Perhaps we can gain some understanding by considering zombies as a conjunction of two ideas. To this effect, zombies have been compared to the concept of a mile-high unicycle (Cottrell, 1999) or to unicorns (Chalmers, 1996, p. 96). The concept of a mile-high unicycle certainly seems coherent; after all, there is nothing in the concepts of either a mile-high object or a unicycle that would lead us to contradiction. The same applies to unicorns, except in this case the conjunction is between a white horse and a single horn. Performing a conjunction on two notions seems to be a relatively straightforward task. Can we think productively about zombies as a conjunction of two ideas, as we do unicorns or tall unicycles?

    The difficulty here lies in the fact that neither the notion of a complete physical replica of ourselves nor the notion of a total lack of phenomenal consciousness are simple notions. They are certainly not nearly as simple as our notions of unicycles and being a mile-high object, or our notions of horses and horns. We can place significant stock in our intuitions in those latter things because of their relatively simple natures. Our notions of consciousness and of our physical makeup, however, are much more complicated and thus much more prone to mistakes of contradiction that we may not discover even after a reasonable amount of consideration. If we have an incomplete notion of either part of our conjunction, we are unable to claim ideal conceivability. Has Chalmers worked out everything that there is to know about the phenomenal realm or at least the aspects relevant for an accurate assessment of a possible conjunction? Does he know the comparable aspects in the physical realm? It seems doubtful that he has adequate knowledge to bless the conjunction unconditionally, which is what his claim of ideal conceivability would imply. Prima facie conceivability does not take him far enough to justify his conceivability to possibility entailment.

    On what grounds can any someone who accepts the conceivability of zombies claim that he or she have better than a prima facie coherent concept of zombies? What assures them that they have sufficient understanding of the relevant concepts to make such a claim? I submit that despite the best of intentions, we still have much work to do. Güven Güzeldere sums it up nicely in his introduction to the anthology The Nature of Consciousness: "If anything, the survey of the contemporary issues and current debates surrounding consciousness points to a need for a careful reexamination of our pretheoretical intuitions and conceptual foundations on which to build better accounts of consciousness." (1997, p. 45) Until clarity prevails over the conceptual disarray surrounding the notion of phenomenal consciousness, we cannot accept without question claims for the ideal conceivability of zombies or, by association, their logical possibility.
 
 

Block, Ned. (1980), ‘Troubles with Functionalism’, in Readings in Philosophy of Psychology, vol. 1, ed. N. Block (Cambridge, Mass.: Harvard UP)

Chalmers, David J. (1996), The Conscious Mind (Oxford: Oxford UP)

Chalmers, David J. (1999), ‘Does Conceivability Entail Possibility?’ (Unpublished first draft, available at http://www.u.arizona.edu/~chalmers/papers/conceivability.html)

Cottrell, Allin. (1999), ‘Sniffing the Camembert: On the Conceivability of Zombies’, Journal of Consciousness Studies, 6 (1), pp. 4-12

Dennett, Daniel. (1995), ‘The Unimagined Preposterousness of Zombies’ in Brainchildren (Cambridge, Mass.: Bradford Books)

Dennett, Daniel. (1999), ‘The Zombic Hunch: Extinction of an Intuition?’ (Given as a Millennial Lecture for the Royal Institute of Philosophy on November 29, 1999. Available at http://www.nyu.edu/gsas/dept/philo/courses/consciousness/papers/DD-zombie.html)

Güzeldere, Güven. (1997), ‘The Many Faces of Consciousness: A Field Guide’ in The Nature of Consciousness, eds. N. Block, O. Flanagan and G. Güzeldere (Cambridge, Mass.: Bradford Books)