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.