The Evidential Argument from Mind-Brain Dependence: A Reply to Bilbo

In my response to Victor Reppert’s anti-naturalistic argument from pain, I stated that a more specific fact (consciousness is dependent upon the physical brain) about consciousness is antecedently more likely on naturalism than on theism. Bilbo provided several feedback messages in response to this claim. As I read him, he thinks the argument is no threat to Christian theists. It is apparently his view that mind-brain dependence is at least as probable on Christian theism as on naturalism, since Christian theists believe in specific, sectarian doctrines that raise the probability of mind-brain dependence. Since I think Bilbo is wrong about this, I’ll explain why.

First, here is the logical form of my evidential argument.

Let D = the mind is dependent upon the physical brain.
Let T = classical theism
Let N = metaphysical naturalism

(1) D is known to be true.
(2) T is not much more probable intrinsically than N.
(3) Pr(D/N) > Pr(D/T).
(4) Other evidence held equal, T is probably false.

Note the modest nature of this argument. It doesn’t claim that theism is probably false; it merely claims that evidence (D), by itself, favors N over T. This distinction is crucial since it allows for the possibility that there could be other evidence that both favors T and outweighs the evidence for N provided by D. Thus, D should be understood as a prime facie reason for rejecting T.

Let me now turn to some of Bilbo’s specific comments.

Bilbo: “My first problem is that it seems more accurate to say that minds *are* the physical brain on Naturalism (not merely dependent on them). And since this has not been demonstrated, it would beg the question to assert that the postulate that “minds are the physical brain” provides evidence for Naturalism.”

That would indeed beg the question, which is why I never said that! My argument is an inductive argument. It would be illegitimate to state the evidence in such a way that entails the hypothesis to be proved. Therefore, I’ll stick with my original formulation of the premise (“the mind is dependent upon the physical brain”).

Bilbo: “But the Christian views I mentioned also make it antecedently probable that minds will be dependent on the brain. Let’s use the structure of your argument with Christian non-reductive physicalism (hereafter NRP)…”

If theism is improbable given D, then so is Christian theism (or any other more specific belief system that entails theism). Christian theism entails theism; therefore it cannot be more probable than theism. Premise (4) entails that, other evidence held equal, Christian theism is probably false.

I don’t deny the potential relevance of sectarian doctrines to the issue of whether my argument is sound. They could raise Pr(D/T) or lower Pr(D/N). In order to assess the evidential significance of such doctrines, we would need to apply a principle that Draper calls the “weighted average principle” (WAP). Let H represent some Christian doctrine. Then WAP can be represented as follows.

Pr(D/T) = Pr(H/T) x Pr(D/T&H;) + Pr(~H/T) x Pr(D/T&~H)

This formula is an average because Pr(H/T) + Pr(~H/T) = 1. It is not a simple straight average, however, since those two values may not equal 1/2.

Let us consider, then, Christian non-reductive physicalism (CNRP), which Bilbo proposes as a specific doctrine that he believes raises the probability of D given (Christian) theism. Bilbo defines CNRP as “the non-existence of all supernatural beings, except for those that are or were at some point divine (angels, demons, God, etc.).” Bilbo claims that CNRP “entails the nonexistence of disembodied human minds.” Using WAP, we obtain the following.

Pr(D/T) = Pr(CNRP/T) x Pr(D/T&CNRP;) + Pr(~CNRP/T) x Pr(D/T&~CNRP)

In order to reject my evidential argument, therefore, Bilbo would need to show that CNRP raises Pr(D/T) so that it is greater than or equal to Pr(D/N) by using the above formula. Does CNRP do that? I shall leave the question as an exercise for the reader.

(Note: I have borrowed heavily from ideas in another paper by Paul Draper, “More Pain and Pleasure: A Reply to Otte.” I am, of course, responsible for any errors in my post.)

About Jeffery Jay Lowder

Jeffery Jay Lowder is President Emeritus of Internet Infidels, Inc., which he co-founded in 1995. He is also co-editor of the book, The Empty Tomb: Jesus Beyond the Grave.

  • http://www.blogger.com/profile/15799168778162687036 Bilbo Bloggins

    Jeff:
    Let D = the mind is dependent upon the physical brain. (Nothing mental happens without something physical happening.)
    Let T = classical theism
    Let N = metaphysical naturalism

    (1) D is known to be true.
    (2) T is not much more probable intrinsically than N.
    (3) Pr(D/N) > Pr(D/T).
    (4) Other evidence held equal, T is probably false.

    Bilbo: I think I see another problem here. The Christian theist will flatly disagree with (1). This also begs the question. D (in the absolute sense which the parenthetical portion of your premise asserts) is not known to be true from the Christian perspective. For instance, the Christian will not concede that we *know* that when the physical body dies, nothing mental happens. How do you justify that premise? In your infidel paper, you argue that the mere correlation of brain and mental states argues for their inability to exist independently. You state that “if nothing mental happens without something physical happening, that strongly implies that the mind cannot exist independently of physical arrangements of matter.” I’m not sure that follows; correlation does not argue towards inseparability. For instance, suppose Amy is fingerpainting with crazy glue and then goes on to play pattycake with Patty. Amy and Patty become temporarily connected so that every movement Amy makes causes a corresponding movement on Patty’s part. After the doctor separates them, they have no trouble existing independently.

    Further, I think many would disagree that D can even be shown in a mortal person in any absolute sense as your premise requires. Showing examples where we do have neural correlates of conscious experience does not imply that a neural correlate of every conscious experience can be found.

    BTW, Jeff – I am probably not going to respond to Steven Carr due to his track record elsewhere. If he makes a point you feel I need to respond to, let me know.

    Jeff: Let me now turn to some of Bilbo’s specific comments.

    Bilbo: “My first problem is that it seems more accurate to say that minds *are* the physical brain on Naturalism (not merely dependent on them). And since this has not been demonstrated, it would beg the question to assert that the postulate that “minds are the physical brain” provides evidence for Naturalism.”

    Jeff: That would indeed beg the question, which is why I never said that! My argument is an inductive argument. It would be illegitimate to state the evidence in such a way that entails the hypothesis to be proved. Therefore, I’ll stick with my original formulation of the premise (“the mind is dependent upon the physical brain”).

    Bilbo: I’m needing clarification here. The problem is – from a naturalistic standpoint, if this doesn’t mean that the mind is the brain, what does this actually mean? Unless you unpack what *mind* means here (e.g. is it physical or non-physical?), I can’t see how I can judge the probability that this state of affairs would come about given N. If it is non-physical, it obviously would not be entailed by N (N does not render it likely that a non-physical thing will depend on or correlate with something physical). So I’m assuming that you have to be meaning “mind” in a physical sense. So then D would actually be “the physical mind is dependent upon the physical brain”, and at this point I’m not really understanding the difference between the two. Are they distinct? What makes the physical mind different from the physical brain? Is the physical mind located somewhere else? Does it have different properties, etc.?

    But, regardless of the answer to those questions, the dualist will just deny this premise in denying that the mind is physical. If we do not know if the mind is entirely physical, we cannot say whether or not D is likely on N.

    Bilbo

  • http://www.blogger.com/profile/10289884295542007401 Jeffery Jay Lowder

    I should not have included my parenthetical comment in the definition of D. I’ll remove it promptly. Would this change your assessment of (1)?

  • http://www.blogger.com/profile/10289884295542007401 Jeffery Jay Lowder

    Bilbo: “I’m needing clarification here.”

    I think the confusion here stems from what is being used as a premise in an argument designed to support naturalism, as opposed to what naturalists may believe. Certainly, my original statement of D did not help matters!

    Allow me to attempt to fix the problem here. While naturalists may believe that the mind just is in some sense a property of the brain, all that is being claimed in the argument at hand is the mind is dependent upon the physical brain. (I have removed the problematic parenthetical statement from the definition of D.) With this more modest definition of D, I think it is being stated in a non-question-begging way such that even proponents of CNRP could accept it.

  • http://www.blogger.com/profile/15799168778162687036 Bilbo Bloggins

    Jeff: I should not have included my parenthetical comment in the definition of D. I’ll remove it promptly. Would this change your assessment of (1)?

    Bilbo: Yes.

    Some other issues.

    Why is this even an argument from mind-brain dependence? Couldn’t it be an argument from the physicality of anything?

    For instance,

    Let F = Firetrucks are physical objects.
    Let T = classical theism
    Let N = metaphysical naturalism

    (1) F is known to be true.
    (2) T is not much more probable intrinsically than N.
    (3) Pr(F/N) > Pr(F/T).
    (4) Other evidence held equal, T is probably false.

    Doesn’t this argument work for any physical object, and thus, isn’t it ultimately a bit absurd?

    Jeff: While naturalists may believe that the mind just is in some sense a property of the brain, all that is being claimed in the argument at hand is the mind is dependent upon the physical brain.

    Bilbo: I’m just not sure how Pr(D/N) can be estimated without knowing what a mind is being defined as. If we don’t know what the state of affairs (mind depending on brain) actually *is*, how can we know if it is probable on N?

    Bilbo

  • http://www.blogger.com/profile/10289884295542007401 Jeffery Jay Lowder

    Bilbo: “Doesn’t this argument work for any physical object, and thus, isn’t it ultimately a bit absurd?”

    No. Unlike minds, theism provides no antecedent reason at all to believe that fire trucks are not physical objects and, therefore, provides no evidence at all favoring naturalism over theism.

  • http://www.blogger.com/profile/10289884295542007401 Jeffery Jay Lowder

    Bilbo: “Bilbo: I’m just not sure how Pr(D/N) can be estimated without knowing what a mind is being defined as.”

    It seems as if “mental states” are easier to define than “mind.” What if I modified the definition of D again and referred to “mental states” instead of the “mind”? Would that be any more clear to you?

  • http://www.blogger.com/profile/15799168778162687036 Bilbo Bloggins

    Ok Jeffrey – brace yourself here. I’m about to possibly say something really stupid. Bear in mind that you’re carrying on a conversation with someone who is very much a neophyte. Your probability calculus in the latter half of this post for instance goes way over my head.

    Now, in looking back over this, it seems to me that no theist will ever accept (1) when stated properly.

    Stating D as “the mind is dependent upon the physical brain” threw me off a bit, as, with “mind” in the singular, I was only thinking in terms of human minds. But, stated more accurately, D should read “all minds are dependent on brains”.

    If I am right here and that is the proper way of stating the premise, this would also beg the question. The theist, believing that at least one mind (God’s) is not dependent on a brain, will not accept (1). No?

    Bilbo

  • http://www.blogger.com/profile/10289884295542007401 Jeffery Jay Lowder

    No. D is intended to refer to the mental states of humans and (other) animals; it is not intended to refer to the mental states of God. So it is not question-begging in the way that you describe.

  • http://www.blogger.com/profile/15799168778162687036 Bilbo Bloggins

    Okay, we can come back to the matter of what a “mental state” is later.

    For now,

    Let D = human mental states are dependent upon a physical brain.

    Is that pretty much what we’ve come down to?

    But then it seems that classical theism provides no antecedent reason to believe that human mental states are not dependent upon a physical brain, as the only disembodied minds it entails are non-human.

    Bilbo

  • http://www.blogger.com/profile/10289884295542007401 Jeffery Jay Lowder

    I cannot agree with your statement, “classical theism provides no antecedent reason to believe that human mental states are not dependent upon a physical brain, as the only disembodied minds it entails are non-human.”

    No antecedent reason? That seems much too strong to me. To quote Draper: “Theism implies an extreme metaphysical dualism–a mind existed prior to the physical world and was responsible for its existence. Thus, on the assumption that theism is true, it is antecedently likely that minds are fundamentally nonphysical entities…” Furthermore, on theism, alternatives to physicalism are somewhat more likely, simply because there is less reason to assume that mental states have to be related to physical states in some way.

  • http://www.blogger.com/profile/15799168778162687036 Bilbo Bloggins

    Jeff: No antecedent reason? That seems much too strong to me. To quote Draper: “Theism implies an extreme metaphysical dualism–a mind existed prior to the physical world and was responsible for its existence. Thus, on the assumption that theism is true, it is antecedently likely that minds are fundamentally nonphysical entities…”

    Bilbo: Interesting stuff.

    But it looks like Draper is not differentiating though, and just subsuming these two very different kinds of entities under one blanket category of “mind”.

    Because there is a metaphysical dualism between God (as Mind) and creation, doesn’t seem to imply at all that creatures themselves will embody this metaphysical dualism. The commonality is there in certain aspects (e.g. human minds are like the divine mind in some ways – first-person perspective, conscious, etc.), but human minds are, on theism, very much different from the divine Mind. They lack all of the omni-attributes of the divine mind which immediately puts them in an entirely and radically different ontological category. On theism, God has created human minds that are already potentially as different from the divine Mind as any one thing can be from another. So it seems that it wouldn’t be surprising or improbable, if, on theism, human minds are different also in the sense that they are embodied. Physical embodiment provides a nice mechanism for the antithesis of certain omni-attributes that God might not want to endow creatures with – spatial location, lack of intrinsic eternality, limitations on knowledge, etc.

    I might have even just convinced myself that human minds/mental states being dependent on the physical (or something like it) ought to be considered antecedently probable on theism. :-)

    Bilbo

  • http://www.blogger.com/profile/02638655574838994630 Victor Reppert

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