El argumento epistemológico en contra del materialismo

By Maverick Christian

To begin, I will quote Alvin Plantinga:

The argument, in essence, is this: that we ordinarily think that the content of a belief, or an intention, or an action is relevant to the actions caused by beliefs, intentions, and actions. I believe that there is a beer in the fridge; we ordinarily think that it is in virtue of its content that this belief causes me to go to the fridge. I intend to get a beer from the fridge and I intend to do so; we ordinarily think that the content of this intention and of carrying it out is causally relevant to my action of going to the fridge. We don’t just ordinarily think these things; they are nothing but sobering truth. I’m going to argue that if materialism about us human beings… were true, then these things are false: It would not be in virtue of their content that beliefs, intentions, and actions do what they do. [1]

For simplicity, let’s just consider beliefs. In materialism, the belief coin has two sides: the neurophysiological/NF properties (certain neurons wire in a certain way, etc.) of the belief, and the actual semantic content of the belief (e.g., there’s a beer in the fridge ). In dualism (the idea that our minds are a composite of the physical brain and a nonphysical mental component, e.g., the soul) it is possible that the content of a belief can modify behavior; e.g., I believe something and on the basis of this belief my soul impacts my neural pathways in a certain way to cause a behavior.

On materialism, however, the content of a belief is causally irrelevant in the sense that (given materialism) a belief causes an effect in virtue of its NF properties, and not in virtue of its content. We can see this by doing a little thought experiment. Suppose a given person’s belief, say, the belief that there is a cold soda in the fridge , had the same NF properties, but a completely different content, such as that the moon is made of green cheese . Would the person’s behavior be different if the belief had the same NF properties, but different content? It wouldn’t, because having the same neurophysiological properties means that we would have the same electrical impulses traveling along the same neural pathways and thus emitting the same muscular contractions. So if materialism were true, the content of our beliefs would be causally irrelevant. The argument in a nutshell is this:

If materialism is true, then the content of our beliefs is causally irrelevant.

But the content of our beliefs is causally relevant.

Therefore, materialism is false.

In response one might say that there is something wrong with the thought experiment, since it is metaphysically impossible for a given set of neurophysiological properties to have distinct semantic content. Even if I were a materialist, this does not seem at all plausible to me. The idea of ​​moving subatomic particles around producing semantic content seems almost mystical, and it seems easily conceivable that there is a possible world in which the same moving subatomic particles generate different semantic content, although as a materialist I would like to believe that this might involve the fine-tuning of some kind of physical necessity that makes the moving subatomic particles generate mental states. Still, to my mind’s eye such an adjustment seems conceivable and metaphysically possible.

But even if it is not possible for a given set of NF properties to have a different semantic content associated with it, does this prevent the statement “If a given set of NF properties were to have a different content, the behavior would be the same” from being meaningfully true? I think not. In philosophy, propositions of the form “If P were true, then Q would be true,” where P is an impossibility, are called counterpossible. There seem to be counterpossible statements that are meaningfully true. For example, suppose the renowned mathematician Kurt Gödel proved a certain theorem; it is impossible for theorems to turn out to be false, since they are necessarily true. However, as Alvin Plantinga points out, “If Mic were to prove that Gödel was wrong, mathematicians everywhere would be astonished; it is not true that if Mic were to prove that Gödel was wrong, mathematicians everywhere would yawn with boredom.” [2] So even if “if a given set of NF properties were to have a different content, it would result in the same behavior” were contra-possible, this does not seem to prevent the statement from being meaningfully true.

Reductive and non-reductionist materialism

Another way to try to avoid the semantic content of a belief being causally irrelevant is to take the view that a belief is just a combination of physical properties; the view that beliefs are reducible to physical states in this sort of way is called reductive materialism . Suppose we have P1, P2, P3… Pn to represent various physical properties (e.g., human neurophysiological properties), and let ∨ represent “or.” A reductive materialist might believe that a certain belief is just the disjunction (a set of things related by “or”) of certain physical properties like these:

P1∨ P2 ∨ P3…

Most likely, on reductive materialism a belief would be (merely) a disjunction of a set of physical properties that constitute a given mental state, something like this where & represents “and”:

(P1& P7 & P11…) ∨ (P5 & P63 &…) ∨…

The “∨” is necessary, since it is possible for different sets of physical states to correspond to a given belief (if materialism is true, for example, it would seem that alien neurophysiologies or mechanical silicon brains could also be configured to have a given belief). The above sort of structure “(A & B) ∨ (C & D & E) ∨…” is what logic and math gurus call a boolean combination . In contrast to reductionist materialism which says that beliefs are reducible to NF properties in the way described above, non-reductionist materialism denies this, but does make the claim that beliefs are determined by physical states. One might believe that a belief emerges from physical properties in a way that is roughly analogous to moisture emerging from the combination of hydrogen and oxygen in H2O.

A reductionist materialist might claim that since beliefs are just a (Boolean) combination of NF properties, it might well be that it is in virtue of having semantic content that a belief is causally relevant (this is not necessarily so, because belief is really a disjunction of sets of NF properties, so it would still be possible for a person’s belief to produce behavior in virtue of its NF properties rather than its semantic content, but a reductionist materialist might believe that it is at least possible for a human being’s belief to produce behavior in virtue of having content).

The problem with reductive materialism

Plantinga argues that even if it is true that a belief is causally relevant in virtue of its having a certain content, it does not follow that the semantic content is itself causally relevant. Plantinga gives the following illustration. Suppose Alvin throws a ball that has a mass of 0.2 kilograms, and the ball hits a glass window, causing it to break. If the ball had been much lighter (say, the mass of a feather), it would not have broken the glass, so the ball breaks the window in virtue of (among other things) its being 0.2 kilograms. Now suppose that the property of having a mass of 0.2 kg is Sam’s favorite property. Thus, we have the following:

Having a mass of 0.2 kg = Sam’s favorite property

Since having a mass of 0.2 kg is Sam’s favorite property (which is not his favorite property by definition, but reductionist materialists similarly do not [normally] believe that the identity relation between a belief and a boolean combination of NF properties holds by definition), then it follows that a ball breaks the window in virtue of having Sam’s favorite property. And yet:

Having a mass of 0.2 kg is Sam’s favorite property.

It doesn’t actually seem to have anything to do with the ball breaking the window, even though it is in virtue of having Sam’s favorite property of the ball breaking the window. Similarly, the fact that a set of NF properties is a belief doesn’t seem to have anything to do with the set of NF properties causing behavior, even though it is true that a belief causes behavior in virtue of having a certain semantic content.

I think we can make this clearer by considering the following thought experiment. Suppose that reductionist materialism is true and a mad scientist inserts a belief interface device (BID) into Smith’s brain, which acts as a new interface between Smith’s belief and behavior. For example, the mad scientist sets up the BID so that when Smith believes that I am thirsty, the NF properties of this belief electrochemically affect the BID and the BID subsequently causes Smith’s body to take a drink of water. The mad scientist can set up the BID at will so that any given belief can cause almost any behavior. For example, the mad scientist sets up the BID so that the NF properties of the belief that drinking water will kill me and I don’t want to die trigger an electrochemical reaction that (thanks to the belief interface device) causes Smith’s body to get a drink of water. The mad scientist sets up the CID again so that the NF properties of the belief that I will never see a Nicolas Cage movie cause Smith to go see a Nicolas Cage movie, and the NF properties of the belief that grass is air cause Smith to eat coconut ice cream after a fish dinner. All of this would be possible on reductionist materialism because a human being’s belief causes effects in virtue of its NF properties, not its semantic content, even if it were the case that beliefs are just (boolean) combinations of NF properties.

The DIC scenario shows that it is the NF properties of a belief and how those properties interact with the rest of the physical system that determines our behavior. DIC may be science fiction, but even in our own naturally occurring belief interface system, it is the NF properties of a belief and how those properties interact with the rest of our physiology that determines our behavior. To look at this slightly differently, let PS1, PS2, PS3… PSn each be a set of physical properties, e.g. PS1 is short for (P1 & P7 & P11…). Now suppose that the semantic content of the belief that I am thirsty is just a boolean combination of the physical properties like this:

PS1∨ PS2 ∨ PS3 ∨… ∨ PSn

Now imagine that Smith’s belief that I am thirsty is PS1. Plantinga would say that Smith’s belief does things in virtue of its physical (in this case, neurophysiological) properties rather than in virtue of the physical properties of being part of the Boolean combination that I am thirsty—just as when the ball breaks the window, in virtue of having a mass of 0.2 kilograms rather than in virtue of having a mass of 0.2 kg being Sam’s favorite property.

We can see that this is the case with any other thought experiment. Modifying Smith’s physiology a little, holding the NF properties of the belief (PS1) constant, and the NF properties of Smith’s belief that I am thirsty could cause something quite different, e.g. the physical properties of PS1 triggering an electrochemical reaction causing Smith to ignore the water around him and have to eat sand instead. This would be physically possible, since it is the NF properties of a belief and how those properties interact with the rest of the physical system that determine our behavior. Given materialism, it would just be a matter of luck (e.g. favorable physical laws) that belief and behavior are linked in a “rational” way by mimicking the semantic content influencing behavior, e.g. the NF properties of the belief that this plant is poisonous and hence I will not eat it causes me not to eat the plant, unlike the NF properties of the belief that grass is air causes me not to eat the plant. In any case, the thought experiment does illustrate that it is the NF properties of the belief and how those properties interact with the rest of the physical system that determine our behavior. Just as having a mass of 0.2 kg being Sam’s favorite property doesn’t seem to have anything to do with why the ball breaks the window, so too does PS1 being a member of the Boolean combination of I’m thirsty not seem to have anything to do with why PS1 does the things it does. If that is true, then the semantic content of a belief seems to be causally irrelevant in the sense that a belief does things in virtue of its NF properties, and not because of its semantic content.

Conclusion

Given materialism, the semantic content of a belief is causally irrelevant in the sense that a belief does things in virtue of its NF properties, not because of its semantic content. If a given set of NF properties had different semantic content, it would result in the same behavior (the same neurophysiological properties means we would have the same electrical impulses traveling along the same neural pathways and thus emitting the same muscle contractions). Even if reductionist materialism were true, beliefs seem to cause behavior in virtue of their NF properties, not because of their semantic content. The DIC scenario in particular illustrates that even on reductionist materialism, the semantic content of a belief can be absolutely unrelated to the person’s external environment when that belief causes behavior, for example, the situation in which the NF properties of the belief that grass is air cause Smith to eat coconut ice cream. So we have the following argument:

If materialism is true, then the content of our beliefs is causally irrelevant.

But the content of our beliefs is causally relevant.

Therefore, materialism is false.

If materialism were true, a belief would do things in virtue of its NF properties and how those properties interact with the rest of the physical system. Even if the semantic content of a belief is just a boolean combination of physical properties, a set of physical properties that is a member of that boolean combination seems to have nothing to do with why that set of physical properties causally affects other things in one’s body, just as having a mass of 0.2 kg being Sam’s favorite property seems to have nothing to do with why the ball breaks the window.

Grades

[1] Plantinga, Alvin. “A New Argument against Materialism” Philosophia Christi 14.1 (Summer 2012) p. 9

[2] Plantinga, Alvin. “A New Argument against Materialism” Philosophia Christi 14.1 (Summer 2012) p. 21

Original Blog: http://bit.ly/2ZVw4bT

Translated and edited by Jairo Izquierdo