How Does Your Brain Actually Think? (The Argument From Reason Revisited) 


Earlier today I wrote a long "combox" comment on the Argument from Reason, which I later decided I should bring out to a more visible space.

The Argument from Reason comes in many forms, all seeking to show that naturalistic explanations for reality are inadequate, in that they don't explain human reasoning capacities very well. It's not, strictly speaking, an argument for Christian theism, but rather an attempt to show that physicalism (also known as materialism or naturalism), a major alternative to theism, doesn't really work. Physicalism is the doctrine that all life is fully explained by the operations of natural law and chance on physical matter; there is nothing extra-natural or supernatural involved. (Victor Reppert has written definitively on the history and several forms of this argument, and continues to blog on it, in two different locations.)

We're breaking into the middle of a discussion here, but I think what's here is fairly self-contained. I post this at the risk of a little confusion. doctor(logic) and Randy have already written follow-up comments to question what I wrote, and there have been answers to them, in turn, from other theists. This creates a second discussion thread on the same material. (Also potentially confusing: I've corrected the proposition numbering [P1, P2, etc.], and now it's different than in the comment I wrote this morning.) I'll just have to hope we can keep it all straight. 

Following this initial quote from doctor(logic), the second person pronouns (you, your, etc.) throughout were originally directed toward him, since this was a response to what he has written.

"All you are showing is that when a deterministic path to a conclusion is dominated by irrelevancy, we don't trust the conclusion. What does that have to do with deterministic paths dominated by relevancy?

"That is, the brain lesions and alcohol that you cite as reasons to doubt a conclusion are clearly elements that interfere with normal functioning of the brain (and mind, curiously!). There is simply no test whatsoever of mechanistic versus non-mechanistic systems in this argument."

I think you're right--with the ellipsis I'm going to add--that I was saying "that when a ... path to a conclusion is dominated by irrelevancy, we don't trust the conclusion." The statement would also be true with the word "deterministic" included; but in this form it is more general and therefore I think it's more useful.

So if a path to a conclusion is dominated by irrelevancy, we don't trust the conclusion. Now the question is whether a mechanistic path can avoid being dominated by irrelevancy. If not, then we have to conclude that mechanistic explanations are inadequate for rationality. (By "mechanistic" here, I include both random and law-determined physical events.) We know:

   P1: At the foundational, atomic or molecular level (under physicalism) the physical brain operates without regard to rationality.

Chemicals combine on the basis of laws of chemical reactions. Electrical events happen according to laws of electrical behavior. Quantum events happen however they happen, with no regard to any rationality.

At the molecular level, there is no regard for, no connection to, propositions in particular. Now, propositions are bearers of truth. (The following is largely from Moreland and Craig's text on Philosophical Foundations for a Christian Worldview. The section I'm quoting is not peculiarly Christian--it's a general exposition of the correspondence theory of truth. This comment is directed toward doctor(logic) who accepts the correspondence theory of truth, so it is not my intention to debate that theory here.) If you are going to accept a correspondence theory of truth, you need a truth-bearer, that which carries the truth: propositions, in other words. Propositions are not identical to sentences or statements. Sentences or statements differ from propositions in that they are sense-perceptible markings, tokens, strings of sounds, gestures, etc. The general problem with sentences or statements as truth-bearers is that they may or may not contain meaning. When they do not contain meaning, they cannot be truth-bearers. When they do contain meaning, they are always expressions of proposition--which leads us back to propositions as truth-bearers.

Thoughts and beliefs are also not truth-bearers; yet again, it is their content, not their momentary instantiations, that carries truth. This leads us again back to propositions, which are the content of thoughts and beliefs.

Now, looking further into a correspondence theory of truth, there also must be a truth-maker--a state of affairs such that the truth-bearer (the proposition) expresses a true fact about that state of affairs. If the proposition is the one expressed in, "Grass is green," then its truth depends on there being a state of affairs such that grass actually is green. Grass's being green (having the property of greenness) is the truth-maker for the proposition expressed in "grass is green." (Obviously there can be falsehood-makers as well. Grass's being a plant is a falsehood-maker to the proposition expressed in, "Grass is a species of animal." But for simplicity I'll just speak of truth-bearers and truth-makers, and let the reader draw the conclusions relating to other possible conditions.)

But that's not all. The correspondence theory of truth requires that there be a truth-bearer, a truth-maker, and also a correspondence relation between them. That relation depends on propositions having "aboutness," which we've been discussing, or "ofness," or "intentionality" (which is the more technical term). Moreland and Craig say (p. 136),

"The intentionality of a proposition is a natural affinity or intrinsic directedness towards its intentional object., i.e., the specific state of affairs it picks out. Thus truth-makers make truth-bearers true, not in the sense that the former stand in an efficient causal relation with the latter and cause them to be true. Rather, the truth-bearer, the proposition, picks out a specific state of affairs due to the proposition's intrinsic intentionality, and that specific state of affairs "makes" the proposition true just in case it actually is the way the proposition represents it to be."

Propositions are not physical. Sentences and statements, identified as the expression of propositions, may be. Print out this comment and you'll have a page of physical sentences, but the propositions expressed by them are not physical. That is the common view, at any rate. Propositions are not physical because they are not located in space (the same proposition can exist in more than one mind at the same time); they are not located in time (the proposition expressed by "all cats are mammals" is true now in the same way it was true a thousand years ago); it need not be grasped by any (finite) person to exist (the proposition expressed by, "AC circuits can by analyzed through complex number mathematics" was true long before AC circuits or complex number mathematics were discovered). These properties of propositions are not seriously in dispute among people who hold to a correspondence theory of truth.

So let's leave Moreland and Craig behind, and backtrack to where we were before, bearing in mind that we have now identified propositions as truth-bearers, and states of affairs as truth-makers. We can now restate an earlier point and say that

   P2: At the foundational, atomic or molecular level (under physicalism) the physical brain operates without regard to truth-bearers.

It follows that at that micro level, the physical brain operates without regard for truth. Physical reactions--mechanistic or random--just are not about truth. They have no propositional characteristics at all. They display law-like consistency, but do not let that mislead you into thinking of "true" in the wrong sense. They may be trustworthy, reliable, dependable, consistent--but those properties are analogues of a different sense of the word "true." They do not relate to rational truth or logical truth, the kind of truth that obtains when a proposition stands in a correspondence relation to a truth-maker.

Whence, then, under physicalism, does a physical event find its connection to truth, or to any proposition at all? We know that thoughts can express propositions, but the physical events that are equated with thoughts (under your version of physicalism) do not seem to admit propositions into their picture.

I'll explain that assertion: You have earlier said that you believe that thoughts just are physical conditions and processes in the brain. That was your response to a question I asked: whether you think thoughts are epiphenomal ("riders" or "passengers" on the events in the brain), or whether thoughts just are events in the brain. (There are other physicalist options, but you have stated your adherence to one option already so we need not explore those.)

Brain events are composed of a hierarchical series of law and chance relations. Law and chance seem to be the only things operating to produce brain events (matter is involved, of course, but without law and chance it is inert; and I'm sure you would not suggest inert matter as your candidate for producing the relevant brain events). Law and chance, then seem to be the only things operating to produce thoughts. But law and chance have no regard for propositions, as I've shown above. If the only things operating to produce thoughts, from the micro level on up to the macro level, are things that have no regard for (no connection to) propositions, then there is no way for thoughts to have any connection to propositions.

Or do you suggest that there is something at the level of thought, at the macro level, that could overrule physical law and quantum chance events? And do you suggest that there is something in some proposed propositional content of macro-level brain events that could overrule law and chance? How could it do that? It seems that the propositional content of thoughts, if such a thing could exist under your physicalism, would be causally effete, ineffective, in the face of the inexorable, unstoppable, undirected operation of law and chance. So you could never say that one thought leads to another, except in the sense that one thought and the next are causally linked by law and chance, which have no concern for propositions or for truth. Let me shorten that last sentence for clarity: You could never say that one thought leads to another except by processes that have no concern for propositions or truth.

So I would propose:

   P3: At the macro level, under physicalism, the physical brain operates without connection to truth-bearers, unless some truth-bearing capacity is introduced from a non-physical source.

And since you equate thought to physical brain events, P4 follows:

   P4: At the macro level, thought has no connection to truth-bearers, unless some truth-bearing capacity is introduced from a non-physical source.

P5 also follows:

   P5: Thought has no connection to truth.

One might propose that the non-physical source of P3 and P4 is something cast up out of just physical conditions--complexity, perhaps. It behooves the person proposing that possibility to show how complex interactions taking place just through law and chance can find a connection to propositions. Remember, law and chance are the only processes operating at every level of the brain. Therefore your physicalism seems to be a commitment to the belief that law and chance can find a connection to propositions. How? Law and chance just have no way to be truth-bearers, at any level of complexity. This is not a failure of imagination ("I can't quite see how law and chance could be truth-bearers or have any meaningful connection to truth-bearers"). It's not in their nature; it's impossible in principle.

doctor(logic) has often used the word "magical" pejoratively toward dualistic or supernaturalistic explanations. I'm wondering whether it fits better here. Somewhere in the hierarchy of law and chance, something magical happens to the brain that permits its events to be truth-bearers. What is that something? How does truth-bearing enter in?

It seems something must be going on beyond what the merely physical.

Related (March 7, 2006): Neural States and Rationality: Can a Materialist Think? (First of a series of four related entries; see the bottom of that post for the list.) 

Posted: Wed - August 29, 2007 at 08:55 PM           |


© 2004-2007 by Tom Gilson. Permission is granted to quote up to two paragraphs of any blog entry, provided that a link back to the original is included or (in print) the website address is provided. Please email me regarding longer quotes. All other rights reserved.

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