The Part Problem
The Part Problem
People talk about the mind-brain problem, but that is strictly inaccurate. The problem isn’t about how the brain as a whole produces consciousness; it’s about how some of it does. It isn’t about how the brain differs from other bodily organs; it’s about how certain parts of it do. The various parts of the brain look very similar and function similarly, but only a subset of brain parts have the magic touch. What makes them so special? What ingredient do they possess that other parts don’t possess? This is what I am calling the part problem. It refocuses the so-called mind-body problem: how do you convert a bit of the brain that doesn’t produce consciousness into a bit that does? It can hardly be a change of location, as if transplanting neurons from the brain stem into the frontal cortex will magically transform them into agents of consciousness (or if it does, we would want to know how). Nor are the consciousness neurons bigger or brighter than the non-conscious neurons. Nor do they fire more rapidly. There seems to be no chemical or anatomical difference. And it can hardly be supposed that God arbitrarily chose these neurons to be consciousness-bearing ones (“I anoint thee guardians of the soul”). The part problem looks like a hard problem—as hard as the mind-body problem, or even harder. For it introduces an element of arbitrariness into the picture: all neurons seem the same yet only some have the power to produce consciousness. Then, in virtue of what do they have this power? Is there just no answer to this—is it just a freak of nature, or evidence of a hidden world? But why this portal instead of that one? It’s like supposing that a given chemical can explode or not explode without changing. Is it the environment of the neuron that makes the difference? But why? The puzzle is almost violently difficult. We might call it the infuriating problem.
Take a part of the brain that has no consciousness associated with it. Now consider a neighboring part that does have a conscious correlate. How does one part grade into the other? Is there some intermediate state of semi-consciousness? Can there be consciousness migration or consciousness spread? Could they change places consciousness-wise? Is the difference exceedingly subtle or quite manifest? Could a tiny variation of shape make all the difference? Neurophysiologists have looked at both types of cells under the microscope and detected no physical difference, and yet the difference could not be more marked. What proportion of brain cells are mentally employed? I have never heard an estimate. Is it mainly unconscious? Is this ratio the same for all animals with a brain? If so, why? When the brain dies consciousness disappears from its precincts, the light goes out, but what physiological difference between the two types of cells accompanies this, if any? If you were trying to build a conscious machine, would you install two types of components, corresponding to the two types of neurons? Is one a necessary condition of the other? When brains evolved did the unconscious neurons appear first and the conscious ones build on this foundation, or were there always the two types? How are the two developmentally scheduled in embryogenesis? Is one more active than the other? There is surely some physical difference, but we are damned if we can see what it is. The whole set-up seems contrary to reason, and yet these are the facts. This division of labor within the brain is a complete mystery. Why are some neurons not conscious? They ought to be if others are. This conundrum appears to favor some sort of substance dualism: are we then to take that possibility more seriously than we have? Materialism seems defeated in the face of it. But then we will be confronted by the problem of how and why the mental substance selects certain neurons as its locus of influence and not others. We thought that neurons contained some special mental ingredient that sets them apart from other cells in the body, but it turns out they don’t, since some neurons have nothing to do with consciousness. So, are neurons really beside the point? Some are correlated with consciousness, but this may not be because they produce consciousness, since some don’t. But then, we are completely in the dark about the basis of consciousness. Maybe we are looking in the wrong place altogether. The part problem makes the mind-brain problem even harder, even more maddening.
Here is a comparison to make the point vivid. Suppose you are investigating water and are interested in explaining its liquid state. You arrive at the theory that liquidity is the loose arrangement of the constituent H2O molecules. Well and good, you think, we have that problem under control. But then you discover, to your surprise, that not all H2O molecules loosely bonded are liquid! How can that be? The molecules are exactly the same as in the liquid water but the water is not liquid! Obviously, your theory of liquidity is wrong, but you can discern no difference between the two cases: here liquidity, there no liquidity—but exactly the same chemical make-up. It seems impossible, but it is an observable fact. Nature has gone mad, or you have (are you hallucinating?). In the one case, the micro properties produce liquidity; in the other, they do not. How can this be? Is there some other source of liquidity that you are somehow missing—a sort of immaterial liquidity?
