Let us suppose, for the sake of exploration the following (false) thesis:
- I am conscious because of a part of me—viz., my brain—engaging in certain computations which could also be engaged in by sophisticated computers, thereby rendering these computers conscious.
- The brain and liver are both proper parts of me.
Now, let us imagine that my liver started doing C-computations within itself, but did not let anything outside it know about this. Normally, livers regulate various biochemical reactions unconsciously (I assume), but let us imagine that my liver became aware of what it was doing through engaging in C-computations on the data available to it. Of course, livers can't willy nilly do that. So, part of my supposition is that the structure of my liver, by a freak of nature or nurture, has shifted in such wise that it became a biochemical computer running C-computations. As long as the liver continued serving my body, with the same external functions, this added sophistication would not (I assume) make it cease to be a part of me.
So now I have two body parts where C-computations go on: my brain and my liver. However, the following is very plausible to me:
- Whatever computations my liver were to perform, I would do not have direct awareness of what is going in my liver, except insofar as the liver transmitted information to its outside.
But now we have a puzzle. In this setup, I am conscious in virtue of the neural computations that my brain engages in, but am not conscious in virtue of the hepatic computations that my liver engages in. Thus, when my neural computation is quiescent due to sleep, but my hepatic computation continue, I am, simpliciter, not conscious. Why? After all, both the brain and the liver are parts of me. The brain also "keeps to itself": it only lets the rest of the body have the outputs of its computation, but the details of it, it keeps to itself, just as in my thought experiment the liver does. The idea in (1) seemed to have been that computational activity by an organic part of me would give rise to consciousness that is mine. But by the same token the hepatic computational activity should give rise to consciousness that is mine.
So what should someone who accepts (1), (2) and (3) (and the various subsidiary assumptions) say about this? Well, I think the best thing to do would be to abandon (1), denying that I think in virtue of computational activity. A second-best solution would be to qualify (2): yes, the brain and the liver are parts of me, but the brain is a more "intimate" or "central" part of me. But note that one cannot explain this intimacy or centrality in terms of the brain's engaging in computational activity. For the liver could do that, too. Could one explain it in terms of how much coordinating the brain actually does of my bodily functions, both voluntary and not? Maybe, but this has to be taken teleologically. For we can imagine as part of the thought experiment that I become paralyzed, and my brain no longer coordinates my bodily functions, but they are in fact coordinated by medical technology. So the defender of (1) who wishes to qualify (2) in this way may have to embrace teleology to account for the difference between the brain and the liver.
But there may be another solution that doesn't seem to involve teleology. One might say that each bundle of C-computational activities gives rise to a conscious being. Thus, perhaps, in my thought experiment, there are two persons, who contingently have all of their parts in common: (a) the neural person that I am, and (b) the hepatic person that I am not. Contingently, because if the liver were replaced by a prosthesis that maintains basic bodily functions, (b) would die, but (a) would continue to exist, while if the brain were replaced by such a prosthesis, (a) would die, but (b) would continue to exist. This view can be seen as a way of qualifying (2): yes, both the brain and the liver are parts of me, but one is an essential part and the other not. On this view, the claim is that:
- I am conscious in virtue of C-computations in an essential part of me.
It is difficult to fix up (4). One might require that the computations take place throughout the whole of the essential part. But supposing that for a while my left brain hemisphere fell asleep while the right continued C-computing (dolphins practice such "unihemispheric sleep"), then the computations would not be taking place throughout the whole of the essential part. But I would, surely, still be aware. I am not sure there is any way of fixing up (4) to avoid the conscious-neuron and unihemispheric sleep counterexamples. If not, and if no other two-persons-in-one-body solution can be articulated, then the teleological solution may be needed.
Final remarks: I think naturalism requires something like (1). If so, then given the plausibility of (2) and (3), naturalists need to accept teleology. But teleology does not fit well into naturalism. So naturalism is in trouble.