Sunday, May 5, 2013

Plantinga’s Argument against Materialism

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The title is a bit of a misnomer, because for sake of space I’ll have to oversimplify it a bit. That said I can sketch an important part of Plantinga’s argument against materialism. To start out with I’ll quote Alvin Plantinga himself:
The argument, in essence, is this: we ordinarily think that the content of a belief, or an intention, or an undertaking is relevant to the actions caused by beliefs, intentions, and undertakings. I believe that there is a beer in the fridge; we ordinarily think it is by virtue of its content that this belief causes me to go over to the fridge. I intend to get a beer from the fridge and undertake to do so; we ordinarily think the content of this intention and undertaking is causally relevant to my action of going to the fridge. Not only do we ordinarily think these things; they are no more than the sober truth. I’ll argue that if materialism about us human beings…were true, then these things would be false: it would not be by virtue of their contents that beliefs, intentions, and undertakings cause what they do.[1]
To simplify, let us just consider beliefs. On materialism, the coin of belief has two sides: the neurophysiological/NP properties (certain neurons being connected in a certain way etc.) of the belief, and the actual semantic content of the belief (e.g. There is a beer in the fridge). On dualism (the view that our minds are a composite of the physical brain and a nonphysical mental component, e.g. the soul) it is possible for a belief’s content to affect 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 behavior.

On materialism however, the content of a belief is causally irrelevant in the sense that (given materialism) a belief causes stuff by virtue of its NP properties, and not by 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 NP properties but an entirely different content—such as The moon is made of green cheese. Would the person’s behavior be any different if the belief had the same NP properties but different content? It would not, because having the same neurophysiological properties means we would have the same electrical impulses travelling down the same neural pathways and thus issuing the same muscular contractions. Thus if materialism were true, the content of our beliefs would be causally irrelevant. The argument in a nutshell then is this:
  1. If materialism is true, then the content of our beliefs is causally irrelevant.
  2. But the content of our beliefs is causally relevant.
  3. Therefore, materialism is false.
In response one could say that there’s something wrong with the thought experiment because it is metaphysically impossible for a given set of neurophysiological properties to have a different semantic content. Even if I were a materialist, I would not find this at all plausible. The idea of moving subatomic particles producing semantic content seems almost mystical, and it seems easily conceivable for there to be a possible world where the same moving subatomic particles generate a different semantic content, albeit as a materialist I would believe this might involve tweaking some sort of physical necessity that makes moving subatomic particles generate mental states. Still, by my lights such a tweaking does seem conceivable and metaphysically possible.

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

Reductive and nonreductive materialism



Another way to try to avoid the semantic content of a belief being causally irrelevant is to adopt the view that a belief just is 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 represent various physical properties (e.g. human neurophysiological properties) and let ∨ represent “or.” A reductive materialist could believe that a given belief is merely the disjunction (a set of things connected by “or”) of certain physical properties like this:
P1 ∨ P2 ∨ P3
More likely, on reductive materialism a belief would (merely) be 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 needed since it’s possible for different sets of physical states to correspond to a given belief (if materialism is true, it seems that e.g. alien neurophysiologies or mechanical silicon brains could also be configured to have a given belief). The above sort of “(A & B) ∨ (C & D & E) ∨...” structure is what logic and math gurus call a Boolean combination. In contrast to reductive materialism which says that beliefs are reducible to NP properties in the way described above, nonreductive materialism denies this but does claim that beliefs are determined by physical states. One could believe that a belief emerges from physical properties in a way that’s roughly analogous to wetness emerging from the combination of hydrogen and oxygen into H2O.

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

The problem with reductive materialism



Plantinga argues that even if it is true that a belief is causally relevant by virtue of it having a certain content, it doesn’t 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 by virtue of (among other things) being 0.2 kilograms. Now suppose the property of having a mass of 0.2 kilograms is Sam’s favorite property. Thus we have the following:

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


Since having a mass of 0.2 kilograms is Sam’s favorite property (it isn’t his favorite property by definition, but reductive materialists similarly don’t [typically] believe the identity relationship between a belief and a Boolean combination of NP properties holds by definition), it follows then that a ball breaks the window by virtue of having Sam’s favorite property. And yet, this:

   Having a mass of 0.2 kilograms is Sam’s favorite property


doesn’t really seem to have anything to do with why the ball breaks the window, even though it is by virtue of having Sam’s favorite property that the ball breaks the window. Similarly, the fact that a set of NP properties is a belief doesn’t seem to have anything to do with why the set of NP properties causes behavior, even if it is true that a belief causes behavior by virtue of having a certain semantic content.

I think we can make this clearer by considering the following thought experiment. Suppose reductive materialism is true and a mad scientist inserts a belief interface device (BID) in Smith’s brain that acts as a new interface between Smith’s belief and behavior. For example, the mad scientist configures the BID so that when Smith believes I am thirsty the NP properties of this belief electrochemically affect the BID and the BID subsequently causes Smith’s body to get a drink of water. The mad scientist can configure the BID at will so that any given belief can cause just about any behavior. For instance, the mad scientist configures the BID so that the NP properties of the belief 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 configures the BID again so that the NP properties of the belief that I will never see a Nicolas Cage movie cause Smith to go see a Nicolas Cage movie and the NP properties of the belief Grass is air cause Smith to eat coconut ice cream after a fish dinner. All this would be possible on reductive materialism because a human’s belief causes stuff by virtue of its NP properties, not its semantic content, even if it were the case that beliefs are just (Boolean) combinations of NP properties.

The BID scenario illustrates that it is a belief’s NP properties and how those properties interact with the rest of the physical system that determines our behavior. The BID may be science fiction, but even in our own naturally-occurring belief interface system, it is a belief’s NP properties 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 constitute a set of physical properties, e.g. PS1 is shorthand for (P1 & P7 & P11…). Now suppose the semantic content of the belief I am thirsty just is a Boolean combination of physical properties like so:
PS1 ∨ PS2 ∨ PS3 ∨…∨ PSn
Now imagine that Smith’s I am thirsty belief is PS1. Plantinga would say that Smith’s belief causes stuff by virtue of its physical (in this case, neurophysiological) properties rather than by virtue of those physical properties being part of the Boolean combination for I am thirsty—just as the ball breaks the window by virtue of having a mass of 0.2 kilograms and not by virtue of having a mass of 0.2 kilograms being Sam’s favorite property.

We can see that’s the case by using another thought experiment. Modify Smith’s physiology a bit while keeping the belief’s NP properties (PS1) constant, and the NP properties of Smith’s I am thirsty belief might cause something very different, e.g. the PS1 physical properties triggering an electrochemical reaction causing Smith to ignore nearby water and having him eat sand instead. This would be physically possible because it is a belief’s NP properties and how those properties interact with the rest of the physical system that determines our behavior. Given materialism, it would only be a matter of luck (e.g. favorable physical laws), that belief and behavior are linked in a “rational” manner that mimics semantic content influencing behavior, e.g. the NP properties of the belief This plant is poisonous so I won’t eat it causing me not to eat a plant, as opposed to the NP properties of the belief Grass is air causing me not to eat the plant. At any rate, the thought experiment does illustrate that it’s the NP properties of a belief and how those properties interact with the rest of the physical system that determines our behavior. Just as having a mass of 0.2 kilograms 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 for I am thirsty doesn’t seem to have anything to do with why PS1 causes the stuff it does. If that’s true, then a belief’s semantic content appears to be causally irrelevant in the sense that a belief causes stuff by virtue of its NP properties, and not by its semantic content.

Conclusion



Given materialism, the semantic content of a belief is causally irrelevant in the sense that a belief causes stuff by virtue of its NP properties, and not by its semantic content. If a given set of NP properties had a different semantic content, the same behavior would result (the same neurophysiological properties means we would have the same electrical impulses travelling down the same neural pathways and thus issuing the same muscular contractions). Even if reductive materialism were true, beliefs appear to cause behavior by virtue of their NP properties, not by their semantic content. The BID scenario in particular illustrates that even on reductive materialism, the semantic content of a belief can be quite unrelated to the person’s external environment when that belief causes behavior, e.g. the situation where the NP properties of the belief Grass is air cause Smith to eat coconut ice cream. We thus have the following argument:
  1. If materialism is true, then the content of our beliefs is causally irrelevant.
  2. But the content of our beliefs is causally relevant.
  3. Therefore, materialism is false.
If materialism were true, a belief causes stuff by virtue of its NP properties and how those properties interact with the rest of the physical system. Even if a belief’s semantic content just is a Boolean combination of physical properties, a set of physical properties being a member of that Boolean combination doesn’t seem to have anything to do with why that set of physical properties causally affects other stuff in one’s body, just as just as having a mass of 0.2 kilograms being Sam’s favorite property doesn’t seem to have anything to do with why the ball breaks the window.




[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

6 comments:

  1. Still it is dificulty understand the whole argument for thouse who doesn't have a extensive knowledge on epistemology like me...

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    1. I simplified what Plantinga said and offered a thought experiment of my own to make it clearer yet, Still, you may have a point. I'm fairly used to analytic philosophy to the point where what seems easy to me might not seem so easy to the layperson (the sort of phenomena I have in mind is called "The Expert Blind Spot" see this brief university web page on the topic).

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  2. The "content" of beliefs on reductionist materialism is identical to the physical structure of some portion of one's brain. This structure is certainly not causally irrelevant.

    The argument must assume in its second premise that materialism is false before it can even get off the ground and, at that point, it has obviously begged the question (though, coming from Plantinga, this should not surprise us at all.)

    As a result, this argument is a trivial failure, and it should be dismissed.

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    1. The "content" of beliefs on reductionist materialism is identical to the physical structure of some portion of one's brain.

      That’s not quite true; as noted in the article you’re responding to, on reductionist materialism the semantic content of belief is identical to a Boolean combination of physical structures, otherwise reductive materialism would be refuted by “multiple realization,” which is the apparent truth that a semantic content can be associated with more than one type of physical structure (e.g. it seems an entity with a completely alien neurophysiology could believe that two plus two equal four) and so the Boolean combination approach would account for this.

      The argument must assume in its second premise that materialism is false before it can even get off the ground

      The second premise is merely that the semantic content of our beliefs is causally relevant; if this premise has “materialism is false” somehow implicit in it (and I don’t see how; it seems you’d need an independent argument for this) that only strengthens the argument further because than premise 1 (if materialism is true, the semantic content of our beliefs is not causally relevant) is that much stronger. If the materialist is forced by logic to reject premise (2), Plantinga’s argument would have served its purpose in raising the intellectual price tag of materialism, not to mention prove an important claim present in the evolutionary argument against naturalism.

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    2. A more directed response:

      On at least one version of reductive materialism,

      Both what you think of as "semantic content" and behavior are determined by physical structures (models) in our brains. On this hypothesis, accurate models produce true semantic content and corresponding behavior.

      If this is true, then the claim that "semantic content" is causally relevant is false--a simple case of mistaking correlation for causation and ignoring a lurking third variable: the models themselves.

      In addition, this does nothing to raise "the intellectual price tag" of materialism.

      The fact that semantic content itself is not causally says nothing about the reliability of our cognitive faculties, if this hypothesis is true. Both behavior and semantic content are determined by models, and enjoy a predictable correlative relationship as a result.

      When it comes to the EAAN, then, we can avoid the entire problem by simply pointing out the possibility that this hypothesis is true. If this hypothesis is true, then:

      Reliable faculties tend to produce accurate models.

      Accurate models make good predictions efficiently.

      Evolution selects for the ability to make good predictions efficiently.

      Thus evolution selects for accurate models.

      Thus evolution selects for reliable faculties.

      And, since reliable faculties tend to produce accurate models and accurate models produce true semantic content, evolution also selects for true semantic content, albeit indirectly.

      There is no bullet to bite, here. Plantinga fails to really think through how mental processes work on naturalism, does not address this fairly obvious hypothesis at all, and simply assumes that it is false by claiming that "semantic content is relevant."

      (I personally think we should use the term "semantic content" differently--more in line with how I use it in the beginning of my last post--but, for now, let's stick to Plantinga's usage.)

      Howevever, if my hypothesis is correct (and neither you nor Plantinga provide any rationale at all for thinking that it is not) then your P2 here is simply false.

      I think that my hypothesis is correct, and you have offered no reason to reject it, so I will reject your p2. As I said, you're basically just begging the question by assuming that my particular materialistic hypothesis is false at this step.

      And since you are simply wrong about the implications of this rejection re: the EAAN, I can basically leave it at that.

      Semantic content is not causally relevant. It is determined by models, such that accurate models produce true semantic content. Accuracy in models is what matters.





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    3. You go on some tangents of the evolutionary argument against naturalism, and since that goes off topic from this article I won’t address that here. You do say this:

      Howevever [sic], if my [materialistic] hypothesis is correct (and neither you nor Plantinga provide any rationale at all for thinking that it is not) then your P2 here is simply false.

      I think that my hypothesis is correct, and you have offered no reason to reject it, so I will reject your p2.


      I have offered a reason to reject it and both me and Plantinga offer some rationale and thinking it is not correct: premise (2), the notion that the semantic content of our beliefs is causally relevant (e.g. when I want a cold soda, the content of There is a cold soda in the fridge has something to do with my going to the cold fridge to get a cold soda).

      What we have here is a disputable point about which is more plausible: (1) materialism; (2) the semantic content of our beliefs is causally relevant. Plenty of people think we have more warrant for (2) than we have for (1), but of course not everyone agrees (as you yourself would appear to illustrate).

      By denying premise (2) you’re adopting a “bite-the-bullet” philosophical strategy, accepting the conclusion of the opponent’s reductio ad absurdum argument. Plantinga’s argument, basically, is that materialism leads to the implausible view of the semantic content of our beliefs being causally irrelevant, and so because of this materialism should be rejected. But you do not find it so implausible, and so we have a disputable point about how implausible it really is.

      Long story short, we’ll probably have to agree to disagree about how implausible it is that premise (2) is false.

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