Friday, February 14, 2014

Materialism, Mental Content and Logical Possibility

An interesting interview with Alvin Plantinga appears in “The Stone” a philosopher’s corner at the NYT. It contains a passage concerning the metaphysical position called “materialism,” i.e., the thesis that the only things that exist are physical objects and their properties. As applied to mind, this means that there is no non-material mind or soul that is in principle separable and independent of the brain. The mind is simply a feature of the brain. When the brain ceases to function, the mind vanishes. Similarly, when current ceases to run through a computer running a sim, the sim ceases to run, ceases to be. This is true even if the structures or hardware items are still around.  Needless to say, if you turn off the current and smash the machine, the sim ceases to run. Similarly, if you shock the brain, starve the brain, destroy it, the mind vanishes.
There are many interesting questions surrounding the position, and its competitor (dualism), that are the stock and trade of philosophy of mind. Plantinga is one of the most penetrating people in that conversation. But, I think he makes a mistake in the following argument. Follow along and see if I’m just being dense. First, the portion of the interview containing the argument (emphasized parts mine), then a couple of reconstructions, and my criticism:

AP: First, if materialism is true, human beings, naturally enough, are material objects. Now what, from this point of view, would a belief be? My belief that Marcel Proust is more subtle that Louis L’Amour, for example? Presumably this belief would have to be a material structure in my brain, say a collection of neurons that sends electrical impulses to other such structures as well as to nerves and muscles, and receives electrical impulses from other structures.
But in addition to such neurophysiological properties, this structure, if it is a belief, would also have to have a content: It would have, say, to be the belief that Proust is more subtle than L’Amour.
GG: So is your suggestion that a neurophysiological structure can’t be a belief? That a belief has to be somehow immaterial?
AP: That may be, but it’s not my point here. I’m interested in the fact that beliefs cause (or at least partly cause) actions. For example, my belief that there is a beer in the fridge (together with my desire to have a beer) can cause me to heave myself out of my comfortable armchair and lumber over to the fridge.
But here’s the important point: It’s by virtue of its material, neurophysiological properties that a belief causes the action. It’s in virtue of those electrical signals sent via efferent nerves to the relevant muscles, that the belief about the beer in the fridge causes me to go to the fridge. It is not by virtue of the content (there is a beer in the fridge) the belief has.
GG: Why do you say that?
AP: Because if this belief — this structure — had a totally different content (even, say, if it was a belief that there is no beer in the fridge) but had the same neurophysiological properties, it would still have caused that same action of going to the fridge. This means that the content of the belief isn’t a cause of the behavior. As far as causing the behavior goes, the content of the belief doesn’t matter.

Reconstruction, first approximation:
Assume materialism is true; (there are no non-physical things)
Beliefs and desires then must be material things or properties of material things.
There is close association of mental properties with neurological function.
Some of these, beliefs, have content, (propositional content or meaning).
Therefore, meanings, contents are properties of collections of neurons.
There must be some account for differences in content between distinct beliefs.
The differences must be accounted for by differences in neural structures or behaviors of structures.
Change a structure, or the behavior of the structure, and you will change the belief; change the content.
Neural structure and behavior also cause gross motor movements.
It is true that differing beliefs or contents can cause similar gross motor movements.
It follows, then, that the belief or content is not a cause of the gross motor behavior.
It seems to me that this last statement simply does not follow from the others.
In terms of immediacy, the most direct causes of motor movement are nerve firings that actuate muscular activity. These in turn, are caused by others, and you can trace the causal chain back to the neurons in the brain that have the contents, etc.
What is more, the fact that different beliefs can eventuate in identical motor movements is hardly surprising.
There are other phenomena that have multiple physical bases or causes. That does not make it the case that one or the other, or all of the causes are not causes of the phenomena.
Light is a simple example. Electric current passed through appropriate gasses will cause photonic emission. So too will heating a filament of tungsten.
If mental states, such as beliefs, and their contents are in fact physical properties of neural structures, then we can understand how it is possible for several different mental states to eventuate in similar gross motor movements.
The human case: Neural structures’ activities give the human brain a subjective first person experiential ‘theater’ which includes beliefs about the world around. By virtue of these subjective states being themselves, physical properties, they can bring about changes in the physical properties of other things (i.e., the first set of neurons down the line toward the muscles). If they do so, they are a part of the cause of that set of consequent motor movements.
By virtue of their also being first person perspectives on the world, (beliefs included), these first neuronal states serve as motivation for action. Thus, the gross motor behaviors come about. Two physical aspects of one object acting upon each other; the physical aspect we usually label “mental” acts on the physical aspect we label “biochemical”. No mystery there. This sort of thing happens all the time. Gravitational forces in the sun affect nuclear structures, for example.
But, maybe I can improve the argument, to show what I am missing. Putting emphasis on the last section which stresses conceivability, you can generate this:
Reconstruction, second approximation:
It is conceivable that the physical events that end with the gross motor movements in question could start somewhere downstream of contents of beliefs.
It is conceivable that the events that end at the fridge could find their start at neural structures (or behaviors of structures)which happen to be associated with content that bears no similarity to any content that normally gets such event trains moving.
If either or both of these are possible, then, it follows that the content plays no causal role.
Once again, I don’t see that this follows, even granted the counter-factuals.  If content Z and content A are both associated with actions of type M on two different occasions, that fact does nothing toward showing that Z or A (or neither) had no causal role in the M events.
If M is caused by something (F) that has no connection with Z or A, this establishes nothing with regard to events of types Z/A serving as causes of other M type events.
The criticism is an old one, aimed at such hypotheticals, pointing out that establishing logical possibility does not necessarily establish anything metaphysically.
It may be conceivable from our present perspective, that radically differing contents can be the starting point for similar trains of events down the neural stream. It may be conceivable that content-less events can bring about the same sorts of trains. Be that as it may, it is also conceivable that only a very few and specific contents CAN initiate such trains of events. It may be that in some heretofore unknown and subtle way, the sorts of events described in the revision are in fact not logically possible. We can certainly conceive of this. You just did, if you understood the sentences that transmitted the thought.
 If this is in fact conceivable and it is also conceivable that such specific contents are in fact instantiated only by a similarly circumscribed set of neural structural/behavioral complexes, then we have established by Cartesian thought experiment that both points of view (this one, and that of the revision) are logically possible, from our present epistemological perspective. It may be the case that content plays no role. It may be the case that it does play an essential role in such events. That is all. As to physical possibility, we know nothing from these conceptual exercises.