Identity, Explanation, and Consciousness: A Reply to Kim

Identity, Explanation, and Consciousness: A Reply to Kim Brian McLaughlin Rutgers University

Huxley on the Mystery of Consciousness • “How it is that anything so remarkable as a state of consciousness comes about as a result of irritating nervous tissue, is just as unaccountable as the appearance of the Djin, where Aladdin rubbed his lamp” (Thomas Huxley 1866)

McGinn on the Mystery • “The specific problem I want to discuss concerns consciousness, the hard nut of the mind-body problem. How is it possible for conscious states to depend upon brain states? How can technicolour phenomenology arise from soggy grey matter?...How could the aggregation of millions of individually insentient neurons generate subjective awareness? We know that brains are the de facto causal basis of consciousness, but we have, it seems, no understanding whatever of how this can be so. It strikes us as miraculous, eerie, even faintly comic. Somehow, we feel, the water of the physical brain is turned into the wine of consciousness, but we draw a total blank on the nature of this conversion…The mind-body problem is the problem of understanding how the miracle is wrought, thus removing the sense of deep mystery.” (McGinn 989, p.394-395)

Chalmers on the Mystery • “There is no question that experience is closely associated with physical processes in systems such as brains. It seems that physical processes give rise to experience, at least in the sense that producing a physical system (such as a brain) with the right physical properties inevitably yields corresponding states of experience. But how and why do physical processes give rise to experience?...This is the central mystery of consciousness” (2000, p.248)

Suppose that we were able to confirm that the following is true: • Correlation Thesis. For any type of state of phenomenal consciousness C there is a type of neuro-scientific state N such that it is nomologically necessary that a being is in C if and only if the being is in N.

The correlation thesis itself would not offer a solution to the problem of the place of phenomenal consciousness in nature. • The correlation thesis is compatible with a variety of would-be solutions to that problem, including analytical functionalism, Cartesian substance-dualism, emergent property dualism, and neutral monism.

Indeed Huxley, McGinn, Chalmers and many other philosophers maintain that the mystery of phenomenal consciousness would remain: How do the neuro-scientific states in question give rise to states of phenomenal consciousness? • How, for example, does N give rise to C, rather than some other kind of state of phenomenal consciousness distinct from C, or no state of phenomenal consciousness at all?

Notice that a presupposition of this how-question is that N gives rise to C. • If we believe that N gives rise to C, then we will wonder how N gives rise to C.

It seems that it will either be a brute, unexplainable fact that N gives rise to C or else there will be some mechanism by which N gives rise to C. • Either way, it is indeed hard to see how the sense of mystery could be dispelled.

If N gives rise to C but not via any mechanism, then it seems that the fact that N gives rise to C will be a brute fact that we will simply have to accept with what the emergentists of the early twentieth century (Alexander and Broad, for instance) called “natural piety.” • Their view was that among the fundamental laws of nature are the laws correlating neuro-scientific states with states of phenomenal consciousness. • In accepting this, we would not be dispelling or removing the mystery of consciousness; we would simply be accepting it, with natural piety, as a fact of life.

But if instead there is some physical mechanism by which N gives rise to C, it is hard to see how knowledge of it could possibly remove the sense of mystery. • For the how-question would recur for the relevant physical factor at work in the mechanism: if N gives rise to C by giving rise to P which, in turn, gives rise to C, then how does P give rise to C?

Were the correlation thesis true, however, one epistemic possibility would be that N does not give rise to C—that the presupposition of the how-question is false. • Rather than N somehow giving rise to C, it might instead be the case that N is C. • There may be one type of state that is conceptualized in two different ways; two concepts—the concept of N and the concept of C—that answer to the same state type.

On this view, the explanation of why N is nomologically correlated with C is that N = C.

Consider, then: • The Identity Thesis. Types of states of phenomenal consciousness are identical with neuro-scientific states. • The identity thesis entails the correlation thesis.

It is a frequently made point that identities are not themselves explainable. • There is no point to the question “Why is A = B?” • There is no point, that is, unless the intent of the question just is to ask why we should believe that A = B. • But that is a request for a justification, not a request for an explanation.

Of course, we should not take the hypothesis that N = C to in fact explain why N is correlated with C unless the identity hypothesis is epistemically justified.

But the point to note is that the justification for the identity hypothesis need not be epistemically prior to the justification for the correlation thesis. • The justification for the identity hypothesis might be that it offers the best explanation of the correlation.

Chris Hill and I have argued jointly and independently that if the correlation thesis were true, then the identity thesis would offer the best explanation of why it is true. • We thus both offer a conditional defense for type materialism or type physicalism for states of phenomenal consciousness. • In their joint paper “Conceptual Analysis, Dualism, and the Explanatory Gap” (Philosophical Review 1999), Ned Block and Robert Stalnaker argue that in the case of states of phenomenal consciousness, type-type psycho-physical identity claims could be defended by inferences to the best explanation.

In his book, Physicalism or Something Near Enough (Princeton 2005), Jaegwon Kim devotes a chapter aptly entitled “Explanatory Arguments for Type Physicalism and Why They Don’t Work” to trying to show that “best explanation defenses” of type physicalism don’t work. • In what remains, I’ll respond to his objections.

Kim’s Main Claims • (1) Despite a surface similarity, the position that Hill and I take is in fact incompatible with the position that Block and Stalnaker take; so we can’t all be right. • (2) There is reason to be skeptical that there is any rule of inference to the best explanation. • (3) In any case, identities are not explanatory; so explanatory arguments are doomed to failure. • (4) Hill and I are best viewed as appealing to a simplicity argument in favor of type identities, while Block and Stalnaker are best viewed as appealing to a causal argument for psycho-physical identities. • (5) Neither simplicity arguments nor causal arguments will establish psycho-physical identities. • (6) The would-be defense of type physicalism is a hopelessly flawed attempt to close the explanatory gap.

Kim has one positive comment on our would-be explanatory arguments. • He applauds the fact that we are trying to offer a positive case for type physicalism, rather than simply sitting back and saying “I think conscious states are type identical with physical states, refute me if you can!”. • He cites Brian Loar in this regard; John Perry’s “antecedent physicalism” also comes to mind.

It should be noted, however, that there is an important role for the “antecedent physicalism” strategy. • For the leading arguments against type physicalism attempt to show that it is a priori false that types of states of phenomenal consciousness are types of physical states. • Moreover, as will become clear in due course, Kim fails to appreciate how work in antecedent physicalism will be incorporated into an explanatory argument for type physicalism.

Kim on Identity and Correlation • Kim states that he agrees with Jack Smart’s (1959) claim that `A is correlated with B’ is incompatible with `A = B’. • As Kim puts it, “identities and correlations exclude each other.” • He claims, moreover, that Stalnaker and Block correctly take identities to exclude correlations, while Hill’s and I mistakenly think that identities explain correlations. • Hill and I take psychophysical identities to be warranted by the fact that they offer the best explanations of correlations. • Block and Stalnaker, however, know better because they recognize that identity is incompatible with correlation. • So despite surface similarities, the Block-Stalnaker position is in fact incompatible with the Hill-McLaughlin position.

In Response • The first point to note is that neither Hill nor I make essential use of the word `correlation’. • The thesis that I call the correlation thesis does not use the word `correlate’ or any of its cognates. • Correlation Thesis. For any type of state of phenomenal consciousness C, there is some type of neuro-scientific state N such that it is nomologically necessary that a being is in C if and only if the being is in N.

Moreover, as Kim himself acknowledges, the type identity thesis implies the correlation thesis. • So by Kim’s own lights, the identity thesis and the correlation thesis are compatible. • That’s what matters. • It’s irrelevant whether the fact that A = B entails that A is not correlated with B.

I cannot, however, resist noting that Smart and Kim are mistaken in thinking that correlation is incompatible with identity.

Smart’s paper was published in 1959, and so a few years prior to H.P. Grice’s 1963 paper, “The Causal Theory of Perception,” a paper in which Grice distinguishes conversational implication from semantic implication. • Smart and Kim have confused a conversational implication with a semantic one.

`A is correlated with B’ may well have the conversational Doubt-or-Denial condition that A = B. • Subtleties aside, in an ordinary conversational context, when making a statement, we are under a prima facie obligation not to make a weaker statement than we know to be true. • Statements of correlation are weaker than statements of identity. • Thus perhaps ordinarily we shouldn’t state that A is correlated with B unless we doubted that A =B, or took ourselves to be in a position to deny that A = B.

But this D-or-D condition is a conversational implication, and so can be cancelled. • And it is cancelled in the kind of explanatory context in question.

In such an explanatory context, we are concerned to do more than provide information: we are concerned to show that a certain claim is made true by another. • That A = B makes it the case that A is correlated with B.

I think that Kim is also mistaken in claiming that Block and Stalnaker take the position that identities exclude correlations.

Kim offers the following quotation from Block and Stalnaker in support of his reading: • “If we believe that heat is correlated with but not identical to molecular kinetic energy, we should regard as legitimate the question of why the correlation exists and what its mechanism is. But once we realize that heat is molecular kinetic energy, questions like this will be seen as wrong-headed.”

Notice that they write, “if we believe that heat is correlated with but not identical to molecular kinetic energy,” which suggests they think identity is compatible with correlation.

Moreover, Block and Stalnaker elsewhere speak of “mere correlation”: • “if we were to accept mere correlations instead of identities” • “identities allow a transfer of explanatory and causal force not allowed by mere correlations”

Correlation is compatible with identity. • Mere correlation is correlation without identity.

Kim has failed to identify any incompatibility between the Hill-McLaughlin position and the Block-Stalnaker position. • In fact, the positions seem to me to be essentially the same.

Block and Stalnaker are of course correct in calling “wrong-headed” the two-part question, Why is there a correlation between heat and molecular kinetic energy and what is the responsible mechanism? • The second half of the question (“What is the mechanism?”) is wrong-headed in that its presupposition is false.

There is no mechanism that explains why heat is correlated with molecular kinetic energy. • Heat is molecular kinetic energy.

Kim on Scientific Explanation • Kim claims: • “In science there seem to be [only] two principal ways of explaining correlations…(1) invoking a single lower-level process…(2) showing the correlated phenomena to be collateral effects of a common cause.”

I (we) claim there is a third way: by pointing out that the correlates are identical. • `Because A = B’ can provide a correct, informative answer to the question `Why is it that A is present when and only when B is?’

Now I think that Kim would acknowledge that identity claims can be informative answers to such why questions. • But he would deny that this suffices for `A = B’ to be explanatory in any scientific sense.

He maintains that scientific explanations provide information about causal history or about an underlying mechanism. • And of course identity claims don’t do either.

In Response • But not all scientific explanations of correlations provide information about causal history or about an underlying mechanism.

When Maxell’s calculations showed that electromagnetic waves have the same speed in a vacuum as the known speed of light, he famously make “the bold conjecture” that light waves = electromagnetic waves.

Maxwell also pointed out that electromagnetic waves are refracted when going from one kind of material to another in a manner that depends on the refractive indices, K, of the material. • When it was established experimentally that light refracted according to the principles that apply to electromagnetic radiation, this was taken to confirm Maxwell’s bold conjecture.

The hypothesis that light waves are electro-magnetic waves was invoked to explain why (1) electromagnetic waves have the same speed in a vacuum as light waves, and why (2) the various refractive indices in materials are exactly the same for light waves and electro-magnetic waves.

This explanation, one of the greatest achievements of classical physics, is an explanation by appeal to identity. • Moreover, the identity claim was arrived at by something like inference to the best explanation.

The Principle of Inference to the Best Explanation • As Kim notes, Hill, Block, and Stalnaker all speak of the principle of inference to the best explanation. • As he also notes, I don’t. • I claim only that psychophysical identities offer the best explanation of psychophysical correlations—best on grounds of overall coherence and theoretical simplicity.

The reason that I didn’t speak of the principle of inference to the best explanation is that no one knows what, exactly, that principle is.

While Block and Stalnaker say they are appealing to the principle of inference to the best explanation, they nowhere state the principle.

Identity, Explanation, and Consciousness: A Reply to Kim