The Identity Theory in 2-D

I plan on writing a series of posts discussing various themes that came up in discussion at the online consciousness conference.

I have long been a type-type identity theorist. There was a time when I thought that I would write my dissertation defending a version of identity theory (in fact the very first talk I gave at a professional meeting was what I thought of as a ‘pre-prospectus’ available here: Saying “I Do” to Identity. I presented this as a poster at the ASSC in Antwerp and as a talk at the SPP in Barcelona (I called this my “European Identity Tour”))…When I approached Michael Devitt about the idea he said that people used to be interested in the identity theory but that people had moved on…it turns out that people are getting re-interested in the identity theory in the wake of work by people like Tom Polger, Chris Hill, and Ned Block. One thing that came out very clearly in the discussion is the difference between the identity theory that Block holds from the kind that I hold. The main difference concerns how we will eventually come to discover the mind-brain identities. Broadly speaking there are two different camps.

It is useful to remind ourselves of what the originators of the identity theory held. In “Is Consciousness a Brain Process?” U. T. Place says,

The answer seems to be that we treat the two sets of observations as observations of the same event in those cases where the technical scientific observations set in the context of the appropriate body of scientific theory provide an explanation of the observation of the man in the street. Thus we conclude that lightning is nothing more than a motion of electric charges, because we know that a motion of electric charges through the atmosphere, such as occurs when lightning is reported, gives rise to the visual stimulation which would lead an observer to report a flash of lightning (p. 58 in Chalmers 2002)

J.J.C. Smart in “sensations and Brain Processes” writes,

Why do I wish to resist [the suggestion that qualia are irreducibly psychial]? Mainly because fo Occam’s razor. It seems to me that science is increasingly giving us a viewpoint whereby organisms are able to be seen as psyico-chemical mecanisms: it seems that even the behavior of man himself will one day be explicable in mechanistic terms…That everything should be explicable in terms of physics (together of course with the descriptions of the ways in which the parts are put together –roughly, biology is to physics as radio-engineering is to electro-magnetism) except the occurrence of sensations seems to me to be frankly unbelievable. Such sensations would be “nomological danglers,” to use Feigl’s expression

We can see here an emphasis on the notions of explanation and parsimony. 16 years later David Lewis and David Armstrong establish the alternative camp. Lewis puts it most clearly when he writes,

Psychophysical identity theorists often say that the identifications they anticipate between mental and neural states are essentially like various uncontroversial theoretical identifications: the identification of water with H2O, of light with electromagnetic radiation, and so on. Such theoretical identifications are usually described as pieces of voluntary theorizing as follows. Theoretical advances make it possible to simplfy total science by positing brdge laws identifying some of the entities discussed in one theory with entities discussed in another theory. In the name of parsimony, we posit those bridge laws forthwith. Identifications are made, not found.

In ‘An Argument for teh Identity Theory,” I claimed that this was a bad picture of psychophysical identification, since a suitable physiological theory could imply psychophysical identites –not merely make it reasonable to posit them for the sake of parsimony. The implication was as follows:

Mental state M=the occupant of causal role R (definition of M)
Neural state N=the occupant of causal role R (by the physiological theory)
Therefore Mental state M=neural state N (by transitivity of =)

Nor is this peculiar to psychophysical identifications. He goes on,

…the usual account is, I claim, wrong; theoretical identifications in general are implied by the theories that make them possible –not posited independantly. This follows from a general hypothesis about the meaning of theoretical terms: that they are definable functionally, by reference to causal roles (Psychophysical and Theoretical Identifications)

In a recent paper on functional reduction Ned Block targets the Lewisian view in favor of the Place/Smart view. Here is what he says,

If we want to know why water = H2O, freezing = molecular lattice formation, heat = molecular kinetic energy, temperature = mean molecular kinetic energy, etc, we have to start with the fact that water, temperature, heat, freezing and other magnitudes form a family of causally inter-related “macro” properties. This macro family is mirrored by a family of “micro” properties: H2O, mean molecular kinetic energy, molecular kinetic energy and formation of a lattice of H2O molecules. (Of course a given level can be micro with respect to one level, macro with respect to another.) The key fact is that the causal and explanatory relations among the macro properties can be explained if we suppose that the following relations hold between the families: that water = H2O, temperature = mean molecular kinetic energy, heat = molecular kinetic energy and freezing = lattice formation. For example, why does decreasing the temperature of water cause it to freeze? Why does ice float on water? Here is a sketch of the explanation: The oxygen atom in the H2O molecule has two pairs of unmated electrons, which attract the hydrogen atoms on other H2O molecules. When the kinetic energy of the molecules decreases, (i.e. the temperature decreases) each oxygen atom tends to attract two hydrogen atoms on the ends of two other H2O molecules. When this process is complete, the result is a lattice in which each oxygen atom is attached to four hydrogen atoms.Ice is this lattice and freezing is the formation of such a lattice, which is why decreasing temperature causes water to freeze. Because of the geometry of the bonds, the lattice has an open, less dense structure than amorphously structured H2O (viz., liquid water)–which is why ice (frozen water) floats on liquid water.

Suppose we reject the assumption that temperature is identical to mean molecular kinetic energy in favor of the assumption that temperature is merely correlated with mean molecular kinetic energy? And suppose we reject the claim that freezing is lattice-formation in favor of a correlation thesis. And likewise for water/H2O. Then we would have an explanation for how something that is correlated with decreasing temperature causes something that is correlated with frozen water to float on something correlated with liquid water, which is not all that we want. The reason to think that the identities are true is that assuming them gives us explanations that we would not otherwise have and does not deprive us of explanations that we already have or raise explanatory puzzles that would not otherwise arise. The idea is not that our reason for thinking these identities are true is that it would be convenient if they were true. Rather, it is that assuming that they are true yields the most explanatory overall picture. In other words, the epistemology of theoretical identity is just a special case of inference to the best explanation. (See Block, 1978a; Block, 2002; Block & Stalnaker,1999).

Block goes on to argue that the Lewis style view is incompatible with the metaphysics of physicalism. Block distinguishes between ontology and metaphysics. Ontological physicalism is just the claim that in our ontological commitment to the existence of qualia we commit ourselves only to physical entities (ontological dualists deny this). Metaphysical physicalism is the claim that qualitative properties are essentially or metaphysically physical. That is to say that all qualitative properties will share the same physical properties in so far as they are physical. the Lewis style physicalism is ontologically but nit metaphysically physicalist. This is because as it happens all of the realizers of mental states are physical but metaphysically pain is a functional state for Lewis and only contingently a physical state. Metaphysical physicalism –real physicalism in Block’s view– says that it is not contingent but necessary that pain is a physical state.

But if we adopt the 2-D framework and put the Lewisian claims in terms of it this is no longer a problem. On this kind of view the functional definition gives us the primary intension of ‘pain’ and the physical state gives us the secondary intension. This allows us to treat ‘pain’ just as we do ‘water’. ‘Water is H2O’ has a contingent primary intension and a necessary secondary intension. So we can update Lewis view that ‘pain’ isn’t a rigid designator as the claim that the primary intension of pain is contingent (just like ‘water’). ‘Pain’ is still a rigid designator in the ordinary sense that its secondary intension is necessary. In all worlds considered as counter-factual pain is a brain state. However we accommodate the conceivability of Martians and disembodied minds by noting that in some worlds considered as actual pain is not a brain state (just as in some worlds considered as actual water is not H2O). This does not threaten the identity; it is the usual way that theoretical identities work. Notice also that this 2-D identity theory is a metaphysical physicalism in Block’s sense and not merely an ontological physicalism.

Of course the real resistance to the 2-D Lewisian identity theory is that qualitative states are not supposed to be functionally definable. In fact Block and Chalmers often talk as though qualitative properties are definable as ‘the not functionally definable properties of experience’ (more on that later). If that is your view then you cannot do the Lewsian deduction of the identity. What are we to make of this? I will come back to this in the next post.


14 thoughts on “The Identity Theory in 2-D

  1. Richard, even independently of the functional definition of qualitative states, it is wrong to treat qualitative state terms as rigid designators of their neural bases. We can understand the possibility that Commander Data’s pain-experience has a different physical basis from ours yet feels the same as ours. But, on the usual story about ‘water’ as rigid, it makes no sense to suppose that water on Mars has a completely different physical basis from water on earth. The point is that a PHENOMENAL definition of a qualitative state term has the same “result” as a Lewis style functional definition in this respect.

    • Hi Ned, thanks for the comment!

      Putnam originally introduced Twin Earth not as existing in some possible world but as an actual planet somewhere in our galaxy. I think that his original idea was something more like the way Jade actually is; that is, he was supposing that we could actually discover that the water on Mars has a completely different physical basis from the water on Earth. If that was the way you thought about water then there would be continuity with the Data case…Kripke talks about this briefly in N & N in the third lecture and suggests that we would at that point either say that there are two kinds of water or we would drop the term ‘water’ altogether (he is talking about gold but the point is the same). But I agree that this way of doing things is to say that water is metaphysically functional as opposed to physical.

      Now, if we take your reading and rule out cases of XYZ in the actual world (as I am inclined to) then I am inclined to take the same line with Commander Data; i.e. a merely functional isomorph is conceivable but not possible (in your terms…I would prefer to say that it is prima facie conceivable but is not ideally conceivable). This is the respect in which the 2-D identity theory differs from Lewis’. He was happy to allow that there could be different physical realizations of pain in the actual world (so he is like Putnam’s original Twin Earth) whereas I claim that once we have made the identity we then know that the identity is necessary because of independent reasoning about identity. Our thinking that Data is possible is explained away in usual Kripkean manner (i.e. we are really conceiving of something else…and this takes us into primary conceivability). So there is no problem with treating qualitative terms as rigid designators of their neural bases.

  2. I don’t understand what is meant by ‘metaphysical physicalism.’ What does it mean to have a property that is ‘essentially physical’? It might help if someone could explain whether the property of having a mass of 3 kg is ‘essentially physical’. Or the property of having temperature X.

    • Hi Eric, thanks for the comment.

      The idea is supposed to be this. A functionalist about belief, say, thinks that the physical system that realizes belief is in a certain sense irrelevant to the thing being a belief. So, take to systems that are physically organized very differently…say REALLY differently like the Chinease nation and my brain…but none the less are functionally identical then both systens have beliefs. Now if one holds that as a matter of fact all of the realizers of belief are in physical systems then one is an ontological physicalist. But my brain and the Chinease nation do not have any physical property in common which we can call a belief. They have a functional property in common which is a totally different kind of property (it is a second order property; i.e. a property of properties). The metaphysical physicalist will claim that there is one unique physical state that all and only beliefs have in common and so they will deny that the Chinease nation can have beliefs.

      I am pretty sure that the identification of temperature with (mean) kinetic motion is supposed to be a metaphysical reduction for Ned as opposed to merely an ontological one (since he offers these kinds of identities as the kind he is interested in and wants to contrast with functional ones)…but maybe he will weigh in on that…

  3. Thanks Richard.

    I assume having 3 kg of mass is essentially physical even though it can be instantiated by light, plasma, gas, antimatter, solid. The sum of the masses of the constituent subatomic particles, where these subatomic mass values are established by basic physics, seems to be a good ‘essentially physical’ definition of mass. Does that seem right?

    That seems reasonable, and the extension to mean kinetic energy of molecules in a gas seems like it should work.

    As for nonessentially physical things, let me consider the biological kind of the heart. I assume hearts are not metaphysically reducible, but are ontologically reducible,. Given that 1) we have good reasons to think that the mind is a biological process, as much part of the nervous system as pumping hearts are part of the circulatory system, and 2) neuroscience is squarely part of biology and already includes prosthetic devices (e.g., brain-machine interface for motor control of robotic arms), it strikes me as strange to think certain mental properties will be a unique biological process that turns out to not be like every other biological process ever discovered (at a metaphysical level).

    • yeah, that’s just is the difference between the functionalist and the physicalist…all Ned wanted to establish was that the Lewis/Kim/Jackson kind of functionalist/physicalism does not capture what the original identity theorists thought was important about physicalism and Ned is trying to defend a theory that does. My only point was that an identity theory in 2-D allows one to do this.

      As for the functionalist intuitions that stem from the way biology works; I *think* the answer is supposed to be that when it comes to cognitive process we do expect this but when it comes to phenomenal consciousness we don’t…I tend to think that all mental states that can be conscious are qualitative (even beliefs) so I think this holds for all mental states but lots of people (Block included) think that you can have a functional theory of beliefs…

  4. On the other hand, when talking about flow of sodium ions across sodium channels, we have to go to the physics of diffusion to get the right answers. Hence, in my last sentence I should have said ‘higher-level biological process’, because obviously physics is important in biology (e.g., retinal phototransduction probably requires QM to explain).

  5. Dear Richard, The relevant lesson from N&N and I&N is that it is totally implausible to treat ‘consciousness’ as a rigid term for a physical essence along the lines of ‘water’. Someone who claims “SEMANTIC intuitions settle the matter: Commander Data is not conscious because he does not have the physical basis of his consciousness-like state that we have” would be refuted by getting at the idea in another way, e.g.: “But still, I want to know–is what it is like for Commander Data to have “pain” like what I have when I have pain.”
    Dear Eric, I agree that the metaphysical nature of a biological kind can in general presumed to be functional rather than physical. Consciousness may be anomalous in this as in so many other respects.

  6. Thanks again Ned for your response. This is very helpful for me.

    I agree that this is the usual lesson taken from N&N but I claim that there are empirical and theoretical reasons to think that this is wrong. To sum up the reasoning: Pain Asymbolia and Dental Fear cases open up conceptual space for the claim that pain and painfulness are only contingently related; In addition all higher-order theories of consciousness predict that pain and painfulness are continently related. So while it is contentious to make this claim it is not contradictory or absurd. So if one accepts this then ‘pain’ can be treated exactly as we treat ‘water’ with no absurdity…true there is some counter-intuitiveness to the position but the counter-intuitiveness can be explained away in the same way that it is in other cases.

    In answer to your question; “But still, I want to know–is what it is like for Commander Data to have “pain” like what I have when I have pain.” The answer is “no” if you take the secondary intension of “pain” and ‘perhaps,” or “yes” if you take the primary intension of “pain” which is just to say that it is (primarily) conceivable but not (secondarily) possible that Data’s pain have the same phenomenal feel as ours….just like the case of water and H2O/XYZ.

  7. Hi Richard,

    Interesting discussion! Perhaps I missed a step, but I am not quite following your argument.

    You claim that if we take the secondary intension of ‘pain’, then what it is like for Data to have pain is different from what it is like for you or me to have pain. Earlier in the post, however, you say that perhaps pain and painfulness are only contingently related. Finally, you want to suggest that the relation between the feel and the brain state is like the water and H2O/XYZ case.

    But I fail to see how the appeal to secondary intensions is supposed to show that what it is like for Data to feel pain is different from what it is like for us to feel pain. If qualitative features are supposed to be analogous to “watery” features, then since it is possible for XYZ to have watery features, it should be possible for Data’s brain to have qualitative features that our brains do. So maybe he does not have pain (just as XYZ isn’t water), but he has painfulness. And isn’t it the painfulness that is at issue here? If it is, then, with Kripke, I don’t see how we are supposed to explain away the appearance of contingency.

  8. Hi Martin, thanks for the comment.

    I claim that if we take the secondary intension of pain then Data is impossible and inconceivable. What is conceivable and possible is that the primary intension of pain pick something else out…just as you say; xyz may be watery and Data’s states may be painful but that is to deal with the primary intension of pain and water. In short I am claiming that painfulness gives us something like the primary intension and here at the actual world that picks out a brain state so that gives us the secondary intension. As Chalmers convincingly showed all Kripkean a posteriori identities have a necessary secondary intension and a contingent primary intension. The conceivability of the primary intension picking out something other than its actual secondary intension is what explains the seeming contingency of identity claims. This is exactly what I have claimed is going on with pain and so I explain the seeming contingency away in just the usual way. To put it in Kripkean terms I claim that one can be in the same epistemic situation as someone who is experiencing pain and not be in a brain state (just as someone can be in the same epistemic situation as someone who is looking at H2O and yet not be looking at H2O).

  9. […] 10. HOT Qualia Realism 9. Am I a Type-Q Materialist? 8. Why I am not a Type-Z Materialist 7. Consciousness, Consciousness, and More Consciousness 6. More on Identity 5. The Singularity, Again 4. HOT Damn! It’s a HO Down-Showdown 3. Attention & Mental Paint 2. Part-Time Zombies 1. The Identity Theory in 2-D […]

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