Building Better Zombies

I’m warning you…

David Chalmers relies in no small way upon his so-called ‘philosophical zombies’ – entities that are like human beings in every respect, physical and psychological, the only teeny, tiny difference being that they are lacking conscious experience – to make his point about consciousness being a basic property, i.e. that it is a mental-kind term that may neither be functionalized nor emergent from some set of physical states of affairs. However, his example doesn’t (and shouldn’t) convince anyone who is not already friendly towards the sorts of consciousness-views offered by the various dualisms and panpsychisms floating about. To pick but one example, Daniel Dennett doesn’t think that Chalmers’ thought experiment does the trick (and is, in any case, very hostile to the proposition that there may be any mental properties which are not emergent from/reducible to physical facts/happenings [1]). And for what it is worth, I don’t think Chalmers’ thought experiment is very compelling either, even though I am more open than is Dennett to possibilities beyond run-of-the-mill reductive/eliminativist physicalist doctrines.

Why should I say this? Chalmers’ uses his zombies thus:

  1. It is conceivable that there might be some possible world wherein there
    are creatures with brains and psychologies such as our own, which are
    functionally identical to our own, but which are lacking conscious experience.
  2. Since it is conceivable that such beings could exist, consciousness is not an emergent property of physical systems assembled (physically or functionally) like our brains, otherwise the zombies in question would be conscious as well.
  3. As such, we may conclude that consciousness is neither simply a product of physical systems arranged in the right way nor functional systems of the right sort. [2]

Obviously, this is a very simplified presentation of his argument (or at least, of the version of his argument with which I am familiar), but it captures something of its thrust. As should be apparent, it is the second premise that causes the argument to fail – simply because something implies no logical contradiction, it does not follow that it is actually possible (in this world or any other). It may well be that in actuality any number of functionally appropriate systems (of which human brains are but one example) will be conscious and nothing else besides – which, not incidentally, is precisely the physicalist position promoted by fellows like Dennett.

The weakness of the argument is unfortunate because I find the (reductive/eliminativist) physicalist’s explanation of consciousness risible [3]. I suspect that the argument could be reworked in order to appeal directly to and make use of the sorts of intuitions held by physicalists of a Dennettian sort, all while avoiding the use of modal arguments (“in some possible world…”). This would make for a more effective argument against functionalist/physicalist accounts of consciousness since, at the outset, it gives them everything that they say they want but leads to the necessary abandonment of some of it. What follows, then, is my own version of a zombie thought experiment that, although leaning heavily on the intuitions Chalmers is mining with his zombies, (I think) does a better job.

Building Better Zombies:

Imagine for the moment that there existed a complete neuroscience. I mean ‘complete’ in the sense that this theory ranges over the entire range of properties of neurons as well as their actions and interactions in the terms with which ordinary science is comfortable (i.e. objectively observable/measurable properties) – there is no hint of ‘woo’ about it.  Moreover, this theory has been subjected to rigorous testing and is as good as proven and is able to predict with near perfection what any particular sort of neuron will do whenever any stimuli one would expect to find in its ordinary operational environment (whether biochemical or electrical) are applied to it in said environment [4]. So, were we to have a single neuron placed before us in a petri dish, we should be able to apply any neurotransmitter or electrical charge under any environmental conditions we should choose to subject the cell to, with absolute certainty that it will react in a specific way. This is all well and good, especially since we would not need to make any reference to mental-kind terms (e.g. consciousness, intentionality, representation) – our neuron is simply caused to produce said effect ‘mechanically’, as it were [5]. Indeed, to make any appeal to mental properties at this low level would be to make a claim which no physicalist would suffer gladly – neurons are just too ‘simple’ to be host to intelligence or consciousness.

From this modest beginning, we should be able to attach a second neuron to the first and to apply some stimulus to one or the other and predict with perfect accuracy what each of them will do, considered individually and as a unit. Once again, this prediction will in no way necessitate a resort to mental-kind terms – we are still firmly in the realm of the objectively explicable – and so again with the addition of a third neuron, and a fourth, and a fifth, etc. With each successive neuronal addition, the behaviours of the whole system will become increasingly complex, but without causing any explanatory or predictive troubles (as I have, after all, stipulated that this is a complete neuroscience). On each iteration, we slowly build a neuronal assembly that is increasingly similar to our own human brains until, soon enough, we will have succeeded in building one that is physically and functionally identical to an ordinary human brain which may then be hooked up in the right way to a (presumably custom-built) body. The zombie is ready.

I told you so!

This zombie will now start interacting with its environment and new stimuli will arise naturally from sensory perception of the immediate environment. This will lead to the zombie behaving in complex ways – e.g. using language and planning its vacation to Maui in the fall – based upon the stimuli it receives. Indeed, its behaviour will seem remarkably similar to our own, as we would expect, given that we designed it to be exactly like a neurotypical human being, but for one crucial difference – its behaviours (ranging from thirst to the writing of forlorn love songs) may be explained entirely without reference to mental-kind terms. After all, why should we explain these behaviours by reference to such terms, since they are just the working-out of neuronal cause and effect, which our ideal neuroscience already accounts for with ease?

Not to do so, however, would necessitate accepting some highly dissatisfactory entailments. If our neuroscience really does explain our zombie’s apparently rich range of behaviours, then because we have built a brain that is physically and functionally indistinguishable from that of a womb-born human being [6], we should seek to use the same theory to explain our own behaviour.  Since everything may be satisfactorily explained without need to refer to consciousness, qualia, thought, etc., then explanations of our own activities will also need make no reference to such things.  The trouble is, we emphatically do have subjective experiences and we are conscious. Given this, there are a number of possible moves the physicalist could make:

  1. Give a reductive/eliminative account of phenomena like volition, thought, consciousness, etc. This is, however, precisely what the stipulated ideal neuroscience has done – it has accounted for all higher-order processes in terms of lower-order neurological functioning – and has led only to the present conundrum.
  2. Deny altogether the existence of the referents of mental-kind terms (or, what is the same, insist on their ‘illusoriness’). This strategy preserves the ‘zombic’ quality of our zombie – our mental-kind term-free explanation is then entirely sufficient – but, because our brains are physically and functionally identical to those of the zombie, we necessarily rob ourselves of consciousness, mind, etc.  This, to me, is a major non-starter [7].
  3. Acknowledge the reality of these higher-order phenomena and give a non-reductive account of their emergence from lower-order ones which don’t exhibit mental properties. This preserves the absence of mentality at lower orders of existence, but introduces problems of its own.  Notably, it requires an account of the precise degree of complexity required for emergence to take place.  Furthermore, ‘emergence’ strikes me as something of a scientific equivalent term for ‘and then a miracle happened’.
  4. Abandon physicalism.  There are plenty of acceptable alternatives (dualism, idealism, panpsychism), although they might not be popular in the faculty lounge.


[1] At this juncture I should say that I am only very generally familiar with Dennett’s take on consciousness. Consciousness Explained is on my to-read list, but I haven’t yet got around to it. If I have said something strictly wrong about Dennett’s position, ignorance is my excuse (albeit, a poor one), but if I have got the gist of his position wrong, feel free to take me to task.

[2] He goes on from there to argue for panpsychism, a doctrine with which I shall not concern myself at present (though I find the idea fascinating, if rather counterintuitive and subject to its own problems).

[3] The problems with physicalist accounts of the mind are, to my mind, several and I should like to do a post dedicated exclusively to them, but this is not the time. NB: I do not discount physicalism in its entirety, however, but only those strains of it which claim to already have provided a complete, adequate explanation of the world and everything in it.  The “near enough” physicalism of Jaegwon Kim or Colin McGinn’s physicalist ‘mysterianism’ do not strike me as problematic.

[4] Necessarily, also, in the lab environment. This is, of course, a highly idealized science, but I’m doing philosophy, so I’m able to stipulate anything I wish in order to explore our intuitions. If magical miniature unicorns could do the trick, that would be fair game – so too with scientific theories which require prohibitively complex computations.

[5] Or, rather, biomechanically or biochemically. Or, for that matter, biophysically (especially if quantum minds are something one finds appealing).

[6] I am assuming here that the causal histories of our zombie brain vs. an ordinary human brain will not be relevant, at least insofar as consciousness is concerned – I think it likely that so long as the brain is up and running it should not matter whether it was built in a petri dish or a mother’s belly.  Of course, the different causal histories almost certainly would be of relevance to matters such as personality or learned skills (to name two).

[7] I can’t fathom how it is possible that consciousness (conscious experience) could be an illusion.  For this to be so, it would be necessary that we experience the illusion of having experience.  This idea is so obviously self-defeating and crazy that I wonder why intelligent people go in for it.


Reading Kim’s “Physicalism…” Chapter One

I have begun reading Jaegwon Kim’s Physicalism, or Something Near Enough (Princeton University Press 2005) as part of my self-directed research program on the hard problem of consciousness.  The book seems promising, both for its clarity and readability (a somewhat uncommon virtue among works of analytic philosophy) and for its organization.  It is split into six chapters that are intended to be read as stand-alone essays (indeed, most of these began life as lecture notes) but which together form a cohesive whole.  The book is intended to provide an argument to the effect that a thoroughgoing physicalism is not an appropriate theory to be applied to ‘the mind’, but that a near-total physicalism that leaves room for qualia is necessary and, importantly, good enough.  On with it!

Chapter 1 – “Mental Causation and Consciousness: Our Two Mind-Body Problems.”

Kim argues that there are two serious obstacles in the philosophy of mind that any modern physicalist theory will have to tackle.  The first of these is the matter of mental causation, of how it is possible that “the mind [can] exert its causal powers in a world that is fundamentally physical” (pp. 7).  Mental causation, whatever its mechanism, is an important concern for physicalists, Kim claims, for three reasons.  Firstly, our understanding of human agency and our moral practice requires that it be our beliefs and desires that cause our actions, not mere physical happenings.  [1]  Secondly, human knowledge requires mental causation (since it is predicated upon our having been in appropriately causally linked “cognitive-relations” with external objects and having reasoned from those relations).  Finally, in order for psychology to serve as a useful descriptive enterprise requires effective causation by mental states/properties – to say that ‘anger’ caused an action is to posit a real thing with causal efficacy (9 – 10).

The second obstacle for physicalists is consciousness, specifically the problem of “how [there can] be such a thing… in a physical world, a world consisting ultimately of nothing but bits of matter distributed over space-time behaving in accordance with physical law” (7).  Consciousness seems less immediately troublesome for the physicalist, but is vitally important in certain contexts.  Ethics, for example, makes much of the distinction between those things with consciousness and those without and even the average person finds consciousness to be highly valuable for the access it provides to things like sunsets, flavours, etc.  So consciousness matters rather more than even some philosophers (Dennett) suppose and is not, in any case, explained simply by compiling a list of “psychoneural correlations” (10 – 13).

The Problem of Mental Causation:

Kim believes that a “minimal physicalism” requires supervenience (that is, all physicalisms must include it but are not necessarily identical to it), which he defines as “the claim that what happens in our mental life is wholly dependent on, and determined by, what happens with our bodily processes” (13 – 14).  Supervenience cannot do the work physicalists want it to, however, because of several of their other assumptions; such as the

  1. “[principle of] causal closure of the physical domain.  If a physical event has a cause at t, then it has a physical cause at t” (15), and the
  2. principle of causal exclusion.  If an event e has a sufficient cause c at t, no event at t distinct from c can be a cause of e (unless this is a genuine case of causal overdetermination)” (17), and the
  3. principle of determinative/generative exclusion.  If the occurrence of an event e, or an instantiation of a property P, is determined/generated by an event c – causally or otherwise – then e‘s occurrence is not determined/generated by any event wholly distinct from or independent of c – unless this is a genuine case of overdetermination” (17).

These assumptions inexorably lead to problems for mental causation on supervenience theses.  M (a mental event) is thought to cause M’ (mental causation), but M’ instantiates because of/is generated by P’ (the physical property upon which it supervenes).  Only one of M or P’ can be the cause of M’ (by appeal to principle 2 above) and, since P’ is sufficient for the instantiation of M’ (whatever else happened in the past), the only way to resolve this problem is by claiming that M causes M’ by causing P’.  Physicalists should reject this, however, for two reasons.  Firstly, it is an instance of cross-domain causation (of a sort excluded by principle 1).  Secondly, M has its own supervenience-base P that is sufficient to cause M’, since it is sufficient to cause P’.  Here, then, is a case of overdetermination of P’ (by both P and M), but in order to avoid it we must abandon mental causation (else we are just iteratively pushing the problem into an infinite regress).  So we have preserved lawful relations between the mental and the physical, but have robbed the mental of all causation, letting all the action take place at the level of the bases of supervenience (19 – 21).

The problem of mental causation is summed up for Kim like this:

Causal efficacy of mental properties is inconsistent with the joint acceptance of the following four claims: (i) physical causal closure, (ii) causal exclusion, (iii) mind-body supervenience, and (iv) mental/physical property dualism – the view that mental properties are irreducible to physical properties” (21 – 22).

And since physicalists cannot reject (i) or (iii) without losing physicalism, and (ii) seems a reasonable metaphysical principle, only (iv) can be given up – reduction of the mental to the physical seems to be in order, but…

Can We Reduce Qualia?

We must be clear about what it is to reduce something.  Kim wants to avoid using Nagel’s bridge laws reductionism [2], finding them inappropriate for their vacuity (they could explain many dualisms) and for reasons he promises to elucidate in a later chapter.  Instead, Kim’s model of reduction of a mental property (e.g. pain) is as follows.  First, we must functionalize the property in question – that is, identify the role it is thought to play, the mechanisms that bring it about, and its probable consequences.  Then, we may identify its ‘realizers’, the things that are necessary for its manifestation (C-fibers, neural activation patterns, etc.).  Kim addresses the matters of multiple realizability, specific realizers, loss of singular ‘pain’ concepts, but none of this is particularly germane here – the upshot is that should functional reduction work, we will have saved the causal powers of pain’s realizers, and mental causal efficacy.  It should be noted, however, that this will only work if mental properties actually are functionally reducible – so are they (22 – 27)?

Kim says that intentional and cognitive properties are, but phenomenological properties (qualia) are not.  To make this case there is no need to resort to “anything as esoteric and controversial as the ‘zombie’ hypothesis much discussed [in philosophy] recently” – rather, all that is required is the modest metaphysical prospect of qualia inversion (to be discussed later in his book) (27).


[1] Kim does not elucidate why this should concern us, familiar as he presumes his audience to be with the philosophical literature, but the broad idea is probably something like this – if what one does happens without reference to things like his desires or beliefs, then his actions no longer seem to be for reasons, and, if not for reasons, then are no more meaningful, praiseworthy or blameworthy than a tree falling in the woods.  Moral responsibility cannot obtain since it is dependent upon the reasons-responsiveness of people and, on this conception, people would not be reasons-responsive.

[2] Wherein a property has been reduced when it is appropriately connected with some “nomologically coextensive property [or properties] in the base domain” by means of these bridge laws (22 – 23).

Dennett’s ‘Deepities’ and His One Simple Policy

While I have several reservations about Dennett’s philosophy, I have to hand it to the man – he has panache.  His written works are like this – narrative and entertaining.  And I love the idea of ‘deepities’.

Again, I have reservations.  He (like Dawkins, et al.) want to make religion a thing of the past and so he offers this policy.  However, he (like Dawkins, et al.) misunderstands people – even if you made Christianity and Islam and Judaism and all the rest disappear tomorrow, people would still be prone to irrational, intolerant and dangerous behaviours.  Neither of the two major murderous ideologies that captured state-control during the twentieth century (that is, communism and fascism/Nazism) sprung from deep-seated religious motivations.  Besides, as long as people desire transcendence, they will believe in it.  In any case, I think that’s a good policy anyway – not least because it might make people mellower about what other people think, but also because there’s just so much fascinating stuff to know!