What's In Your Head, Zombie?

Reference Material:
The Conscious Mind by David Chalmers

        My last post mentioned a way of approaching naturalism that we now continue here. The basic idea is to consider the ontological status of certain entities that seem inadequately accounted for by a purely physical description of the world. We ask questions of the form: given naturalism, what about x? Today, x is consciousness, and the discussion will center on an inquiry of David Chalmers’ The Conscious Mind. Roughly speaking, Chalmers’ general conclusion is that physicalism is false because it cannot account for consciousness. Let’s see how he gets there.
        First let’s try to be as clear as possible about what we mean when we talk about consciousness. There are many ways to try to nail down the concept. One is Thomas Nagel’s conception – roughly, someone’s consciousness is what it is like to be them. Another way is to stress the 1st-person, subjective character of consciousness, contrasted against the 3rd-person, objective character of, for example, scientific explanations of phenomena. Chalmers mentions a third. Consciousness is more or less synonymous with experience – a person’s consciousness at any given moment is the experience they are having at that moment. Some blend of these three formulations is about as precise as we can be at this point (or maybe ever).
        Now on to Chalmers’ argument. The first premise, as I see it, is that consciousness is real, and we have to take it seriously. How do we know consciousness is real? We can let Chalmers explain:
  • “It seems to me that we are surer of the existence of conscious experience than we are of anything else in the world.” (xii)
  • “We know about consciousness more directly than we know about anything else.” (xii)
  • “There is nothing we know about more directly than consciousness.” (3)
  • “We know consciousness far more intimately than we know the rest of the world.” (3)
  • “It is the most vivid of phenomena; nothing is more real to us.” (3)
  • “Yet, we know, directly, that there is conscious experience.” (4)
  • “Our grounds for belief in consciousness derive solely from our own experience of it.” (101)
And in more detail later in the book:

“I think the answer to this is clear: it is having the experiences that justifies the beliefs. For example, the very fact that I have a red experience now provides justification for my belief that I am having a red experience. Change the red experience to a different sort of experience, or remove it altogether, and the chief source of justification for my belief is removed. When I believe that I am experiencing a loud noise, my warrant for that belief stems chiefly from my experience of a loud noise. Indeed, one might ask, from where else could it stem”? (196) 

So we know consciousness is real because we have some sort of direct connection to it, a connection that perhaps exists only for consciousness, nothing else. And we have to take it seriously precisely for this same reason:
  • “My knowledge of consciousness, in the first instance, comes from my own case, not from any external observation. It is my first-person experience of consciousness that forces the problem on me.” (101)
  • “Eliminativism about conscious experience is an unreasonable position only because of our own acquaintance with it. If it were not for this direct knowledge, consciousness could go the way of the vital spirit.” (102)
Without wholeheartedly agreeing, this all sounds fairly plausible. To understand the next steps in Chalmers’ argument, we require some background. We first need the notion of supervenience. Roughly speaking, some set of facts B supervenes on another set of facts A if there cannot be a difference in the B facts without a corresponding difference in the A facts. For example, the temperature of a gas (a B fact) supervenes on the kinetic energy of the gas molecules (an A fact) – in order to realize a change in the temperature, a change in the molecular kinetic energy must be effected.
        Notice that a modal notion, a notion of possibility, lurks within the definition of supervenience. For B facts to supervene on A facts is for it to be impossible for the B facts to differ without the A facts also differing. Because supervenience invokes possibility, one must specify the kind of possibility being referenced for supervenience to be precise. Two types of possibility, and therefore two types of supervenience, are important in Chalmers’ argument: logical and natural. Let’s briefly recap/update material I touched on in my possibility posts and define these two notions of possibility.
        Logical possibility is basically equivalent to conceivability. Roughly speaking, if you can conceive of something without producing some kind of logical contradiction or internal incoherence, then that something is logically possible. Dragons driving Porche’s are logically possible. Married bachelors are not. A world where teapots orbit Pluto is logically possible. A world where 2 + 2 = 5 is not. Natural possibility, on the other hand, is possibility given the laws of nature. Supersonic travel is naturally possible; superluminal travel is not.
        To be explicit, let’s combine the distinct notions of possibility and the definition of supervenience. B facts [logically, naturally] supervene on A facts if it is [logically, naturally] impossible for B facts to differ without the A facts also differing. Note that logical supervenience is a stronger notion than natural supervenience. To demonstrate natural supervenience, you need only show that the laws of nature do not permit B facts to differ without a corresponding difference in the A facts. To show logical supervenience, you have to show that B facts differing without A facts differing produces a logical contradiction, a more difficult task.
        We’re finally in a position to understand the main thrust of Chalmers’ argument:
  1. “Materialism is true if all the positive facts about the world are globally logically supervenient on the physical facts” (41).
  2. Consciousness is not logically supervenient on the physical.
  3. Therefore, materialism is false.
The key to this argument turns out to be the reliance on logical supervenience (rather than, say, natural supervenience). I confess – I don’t really understand why logical supervenience is the version of supervenience that must be employed here. There are some arguments in the book, but they are, quite frankly, beyond me. However, for the points I want to make, we can accept the use of logical supervenience for the sake of argument and press ahead. So let’s grant 1 and focus on 2.
        One way Chalmers motivates 2 is through the logical possibility of philosophical zombies. Zombies are beings that are biologically human (they behave in every way like humans), except that they are not conscious. You might say “the lights are on, but nobody’s home” – to all outward appearances, they are identical to humans, except they have no inner experience. There is nothing it is like to be them. Chalmers’ claim is that zombies are logically possible, though confessing that “in some ways an assertion of this logical possibility comes down to a brute intuition” (96). The idea is that if zombies are logically possible, then comparing zombies and humans yields a case where the biological facts are the same, but the facts about consciousness differ. Therefore, consciousness must not be logically supervenient on the physical.
        This direction of argument is fine as it goes, but it’s important to realize that the logical possibility of zombies does not just motivate 2 – it is also implied by 2. If consciousness is not logically supervenient on the physical facts, then it is logically possible for consciousness to be absent in a human despite fixing all the physical facts about that human. In other words, zombies are logically possible. All this is to say that Chalmers must own the consequences of the logical possibility of zombies. And here are where the problems start for Chalmers, for these consequences are bewilderingly counterintuitive.
        Consider Chalmers’ logically possible “zombie twin”. He is a version of Chalmers, physically identical in every respect, except he is not conscious. He claims he is conscious, constructs theories of consciousness, writes them down in books about consciousness, and on an on. And yet, he is not conscious. Now note that everything zombie Chalmers says and writes about consciousness is a physical phenomenon, having a physical cause and a physical explanation, perhaps couched in the language of psychology. (If you’re skeptical here, accept the claim for the sake of argument, given that Chalmers does – “modulo conscious experience… all positive facts are logically supervenient on the physical” (87)). Importantly, consciousness itself never enters into any of these explanations – after all, zombie Chalmers isn’t conscious. Put more succinctly – zombie Chalmers claims he’s conscious, but his consciousness doesn’t cause him to claim this… because he’s not conscious.
        But wait – zombie Chalmers and Chalmers are physically identical, down to the last molecule. Therefore, any physical cause of zombie Chalmers’ behavior also causes Chalmers’ behavior. So everything Chalmers says and writes about consciousness has a purely physical cause, a cause which is completely independent of consciousness. Now nothing about this zombie twin thought exercise was specific to Chalmers, so it generalizes. We are left with the utterly bizarre conclusion that consciousness is causally and explanatorily irrelevant to our claiming that we are conscious, indeed, to our knowledge that we are conscious.
        Now Chalmers acknowledges the counterintuitive nature of this conclusion, for “one would surely be inclined to think that the fact that I am conscious will be part of the explanation of why I say that I am conscious, or why I judge that I am conscious; and yet it seems that this is not so” (182). The frustrating part is that he never seems to balance this bizarre conclusion against the intuition holding up the other side of the argument – that zombies are logically possible. Maybe they aren’t, for reasons we don’t quite understand. For me, this seems way more plausible than the claim that my consciousness has absolutely nothing to do with the fact that I claim I’m conscious.
        And the frustrations continue. Remember where Chalmers’ argument starts? Consciousness is real, and we know it’s real because we are connected to it more directly than anything else in the world. Our knowledge of consciousness comes directly from within, forcing us to take it seriously. What is more, consciousness is bound up with our cognition:
  • “There are deep and fundamental ties between consciousness and cognition.” (172)
  • “These relations between consciousness and cognition are not arbitrary and capricious, but systematic.” (172)
  • “the nature of cognition is not irrelevant to consciousness, but central to its explanation.” (172)
And yet, at the same time, consciousness is somehow causally and explanatorily irrelevant to our cognition. If it played a causal role in cognition, this would manifest itself in behavioral differences between Chalmers and zombie Chalmers, differences precluded by zombie Chalmers’ logical possibility.
        At this point, the counterintuitive implications of the logical possibility of zombies are starting to seem outright contradictory. As a result, I take Chalmers’ argument as a great indication that zombies are actually logically impossible, for reasons we may not understand at this point. This is not an argument from ignorance, simply a comparison of the intuitive acceptability of two claims – zombies are logically possible, consciousness doesn’t cause me to claim I’m conscious – and an assertion that the latter seems outlandish, while the former could very well be false.
        To close, I should mention that Chalmers does describe, almost in passing, the position that I align myself most closely with in the philosophy of mind:

“Don’t-have-a-clue materialism. “I don’t have a clue about consciousness. It seems utterly mysterious to me. But it must be physical, as materialism must be true.” (162) 

Now, it’s not that I think materialism must be true. But there is so much good evidence for it being true (from the physical sciences) that an argument claiming to demonstrate its falsity better be pretty solid. In particular, such an argument better not have implications so counterintuitive as to border on the incoherent.