Natural Metaphysics Blowing Through the Air

In November 2009 the Center for Ethics and Values in the Sciences at the University of Alabama Birmingham hosted a conference entitled Does Scientific Naturalism Exclude Metaphysics? The speakers were Michael Friedman, Andrew Melnyck, Ron Giere, Mark Wilson, Don Ross, Daniel Dennett, J T Ismael, James Ladyman, and Paul Humphries. The conference was video taped and the videos are now up on YouTube  here courtesy of Sarah Vollmer and her graduate student Morgan Anders who are also in the process of making a short documentary film on the issues raised.

The conference focused on Ladyman and Ross’ new book Everything Must Go: Metaphysics Naturalized where they argue, first that scientism is true and second that a lot of contemporary metaphysics, even from philosophers who claim to be naturalists, physicalists, and scientismists (Armstrong is cited as an example), relies on a fundamentally misguided and outdated conception of scientific reality as consisting of little billiard balls flying around in space banging into each other, you know basically the idea that Democritus had 2,500 years ago. Scienticism is the view that science, in particular physics and the methods it employs, is the only real way to know about the world. A priori reasoning on this view is no good, especially when it is detached from science or especially when it employs this outdated model of the scientific model. They argue that the proper role of metaphysics is that of elucidating the connections between the various special sciences so that they form a unified picture of the nature of reality. This is a task that falls to no specific science and so can be called metaphysics (they cite as an example the claim that chemistry unified is physics and physics unified is metaphysics).

My own reaction is to be sympathetic to the criticism of philosophers who try to derive conclusions about the actual world from current a priori reasoning. Given the track record it is far from clear that a priori intuitions are a good guide to the nature of the actual world. They are however a fine guide to the possible worlds. A priori reasoning fills out the space of possible and impossible worlds and science then locates the actual world in that space. The “fictional world” that occupied David Lewis, David Armstrong, as well as philosophers like Locke, Hume, and Kant, is a perfectly respectable possible world and is interesting in so far as it is a live option, which roughly means that it hasn’t been ruled out by scientific inquiry. The main thrust of Ladyman and Ross can then be seen as an argument that science doesn’t bear this picture out and so naturalistically minded philosophers should stop thinking about one set of possible worlds. But nothing in the argument suggests that a priori reasoning about a different set of possible worlds wouldn’t be useful. In fact we need the a priori reasoning about possibilities to make sense of the empirical data and this is the way we will ultimately identify the the mind with the brain, for instance. .

What we get from this kind of picture is a two-dimensional view on which a priori reasoning gives us the primary intensions of statements and science gives us the secondary intensions, or to put it in more Kripkean terms, the job of science is to reduce the epistemically possible to the metaphysically possible. This is still an empiricist position broadly construed since the claim is that for beings like us the only way to know about the actual world is via empirical means. In fact i would count this as a scientismist position. This is perfectly consistent with the claim that an ideal agent who knew all of the facts would be in a position to know about the actual world in an a priori manner.

108th Philosophers’ Carnival

Welcome to the 108th edition of the Philosophers’ Carnival! I don’t know what is going on with the Carnival but  the last few editions have not had very many interesting submissions and I did not get a lot of acceptable submissions for this issue…but I know that there are interesting posts out there  so I scoured the internets to find the best that the philosophy blogosphere has to offer…I also checked a few other disciplines for some food for thought.
  1. Tuomas Tahko presents Draft: The Metaphysical Status of Modal Statements posted at
  2. Andrew Bernardin presents Beneath Reason: An Iceburg of Unconscious Processes posted at 360 Degree Skeptic.
  3. Eric Michael Johnson presents Chimpanzees Prefer Fair Play To Reaping An Unjust Reward posted at The Primate Diaries.
  4. Terrance Tomkow presents Means and Ends posted at, saying, “If your only available means of doing something are impermissible, does it follow that it is impermissible for you to do that thing? Judith Jarvis Thomson says, “yes”. Tomkow argues, “no”.”
  5. Thom Brooks presents The Brooks Blog: Thom Brooks on “A New Problem with the Capabilities Approach” posted at The Brooks Blog.
  1. Over at Conscious Entities Peter discusses Justin Sytsma’s recent JCS paper in Skeptical Folk Theory Theory Theory
  2. Over at Alexander Pruss’s Blog said blogger discusses Video Games as Art
  3. Not to long ago we had a very interesting post over at Brains on breeding pain free livestock. Anton Alterman has a somewhat polemical but interesting response at Brain Scam in Pains in the Brain: On LIberating Animals from Feeling
  4. Over at Siris we are reminded how malleable language is and the effect it has on reading past philosophers in Every Event Has a Cause
  5. Over at Practical Ethics Toby Ord asks Is It Wrong to Vote Tactically? I don’t want to spoil it for you but he thinks the answer is ‘no’
  6. Over at Evolving Thoughts John Wilkins discusses Plantinga’s argument that naturalism is self-refuting in You and Me, Baby, Ain’t Nothing But Mammals
  7. Did you know that a Quine is a computer program that can print its own code? It’s true and over at A Piece of Our Mind John Ku discusses them in Meta Monday: Ruby Quines
  8. Over at Neuroschannells Eric sums up his current views on perception and consciousness in Consciousness (13): The Interpreter versus the Scribe
  9. Over at Specter of Reason there is a discussion of Pete Mandik’s Swamp Mary thought experiment in Swamp Deviants, Part II
  10. Over at the Arche Methodology Blog Derek Ball asks Do Philosophers Seek Knowledge? Should They?
  11. Over at Philosophy on the Mesa Nina Rosenstrand wonders if Neanderthal’s raped early Humans in They Are Us? News from the Primate Research Front
  12. Is the idea that the mind in the head an a priori prejudice? Ken Aizawa thinks not in So, why does common sense say the mind is in the head?
  13. Over at Inter Kant Gary Benham discusses Free Speech and Twitter
  14. Over at The Ethical Werewolf Neil Shinhababu discusses his recent run on Bloggingheads and Hedonism
  15. Over at Logical Matters Peter Smith talks about Squeezing Arguments and comments on Fields characterization of them in Saving Truth from Paradox
  16. Over at In Living Color Jean Kazez discusses just how outrageous espousing moral realism really is in Torturing Babies Just for Fun is Wrong
  17. Over at Philosophy Talk: The Blog Ken Taylor discusses Culture and Mental Illness
  18. Over at In the Space of Reasons Tim Thornton discusses Aesthetic Self-Knowledge
  19. Over at the Philosophy North Blog Aiden McGlyn discusses The Problem of Vanishing Warrant
  20. Finally, have you heard about this Philosopher’s Football match? Virtual Philosopher has a nice report of the madness in Philosopher’s Football -Match Report from the Ref.
That concludes this edition. Submit your blog article to the next edition of philosophers’ carnivalusing our carnival submission form. Past posts and future hosts can be found on our blog carnival |

More on Identity

In his 2004 paper How Can we Construct a Science of Consciousness? Dave Chalmers says,

Where there is systematic covariation between two classes of data, we can expect systematic principles to underlie and explain the covariation. In the case of consciousness, we can expect systematic bridging principles to underlie and explain the covariation between third-person data and first-person data. A theory of consciousness will ultimately be a theory of these principles…

In the third-person facts are all of the functional characterizations typically appealed to by the Lewisian. In the first-person data we find such things as that blue is more like purple than it is like orange and that pain has a certain phenomenal feel, etc. What kind of fundamental principles can we expect? Chalmers gives us a couple of examples in his Facing Up to the Problem of Consciousness. First he postulates “the principle of structural coherence” which he characterizes as;

This is a principle of coherence between the structure of consciousness and the structure of awareness. Recall that “awareness” was used earlier to refer to the various functional phenomena that are associated with consciousness. I am now using it to refer to a somewhat more specific process in the cognitive underpinnings of experience. In particular, the contents of awareness are to be understood as those information contents that are accessible to central systems, and brought to bear in a widespread way in the control of behavior.

In short, then, phenomenal consciousness correlates with what states we access or are aware of ourselves as being in. The second principle is that of “functional invariance” which he characterizes as follows;

This principle states that any two systems with the same fine-grained functional organization will have qualitatively identical experiences. If the causal patterns of neural organization were duplicated in silicon, for example, with a silicon chip for every neuron and the same patterns of interaction, then the same experiences would arise.

These principles are not fundamental but can be explained by some more basic principle and here Chamers offers the dual aspect of information principle;

This leads to a natural hypothesis: that information (or at least some information) has two basic aspects, a physical aspect and a phenomenal aspect. This has the status of a basic principle that might underlie and explain the emergence of experience from the physical. Experience arises by virtue of its status as one aspect of information, when the other aspect is found embodied in physical processing.

At this point one may wonder why we shouldn’t identify the phenomenal properties with the physical properties…Chalmers, in the 2004 paper, says this;

…What would this entail about the relationship between physical processes and consciousness? The existence of such principles is compatible with different philosophical views. One might regard the principles as laws connecting two fundamentally different domains (Descartes 1641/1996; Popper and Eccles 1977). One might regard them as laws connecting two aspects of the same thing (Lockwood 1989; Chalmers 1996). Or one might regard them as grounding an identification between properties of consciousness and physical properties (Smart 1959; Papineau 2002). Such principles could also be combined with different views of the causal relation between physical processes and consciousness (see Chalmers 2002).

So Dave does acknowledge that one might take these correlations to ground an identity claim. Interestingly he seems to take the way that the identity claim will be established as via thinking about parsimony. I suppose that Ned will argue that asserting the identity allows for explanations that we would not have otherwise. Both of these seem like fine reasons to posit the identity. What will the 2-D theorist say? it seems to me that the principle of structural coherence is exactly what gives us the functional foothold that we need to identify the biological basis of experience. What we need then is to determine whether the principle of structural coherence gives us any reason to think that some kind of higher-order theory is right.

UPDATE: It just occurred to me one might use the above kind of considerations to argue that Maria will be able to make the deductions from P to Q (and vice versa) a priori…if so then that would be an independent argument for the identity of the two sets of properties.

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.

The Matrix & Nonphysical Properties

(cross-posted at Brains)

I have long wondered what dualists mean when they speak of nonphysical properties. Today I was reading Chalmers’ paper The Matrix as Metaphysics and he says something that may shed some light on the way in which he thinks of nonphysical properties. He argues that the matrix scenario can be construed as a metaphysical hypothesis about the ultimate nature of the physical world. If this is right then there is a sense in which dualism is true. The mind is a distinct entity that exists outside of physical space-time and causal interacts with the physical body. This is because the physical theory that is true of reality in the matrix is a computational theory on which the ultimate things which exist are bits (zeros and ones). Thus brains in the matrix are ultimately composed of bits and when people in the matrix talk about brains they ultimately are talking about bits. The brain which is outside of the matrix is not composed of bits (let us assume). It is ultimately composed of something else (let’s say strings). Thus the brain outside the matrix, when viewed from the perspective of someone who is in the matrix, is nonphysical. It is not something that could be deduced from a completed matrix microphysics (which would be phrased in terms of ones and zeros).

One might wonder whether a completed matrix physics would have to be supplemented with (from the perspective of the matrix) nonphysical laws in order to capture outside the matrix facts or whether we might view the truly completed matrix physics as being expanded to include the outside the matrix physics. On this latter view the laws of matrix-physics would be a special subset of the laws of outside-physics. If this were true then the matrix-physics would not be complete until it was expanded to include outside-physics and physicalism could still be true. One might also wonder whether people in the matrix had largely true outside-physics beliefs since the matrix world is a deliberate simulation of outside-physics.

But even setting aside these issues there are strange results. Suppose that physicalism is true and that consciousness is a purely physical property of the brain. Let us also assume that this is true of a brain that is not in a matrix scenario. Call this scenario 1. Now imagine that a physical duplicate of this physicalist brain that has been in a matrix scenario since birth Call this scenario 2). Then physicalism is true in scenario 1 and dualism is true of scenario 2. But these brains are physically identical! Furthermore this shows that we could not resolve the dispute between the physicalist and the dualist until one was in a position to determine whether or not one is in a matrix scenario. Since Chalmers himself admits that he cannot a priori rule out that he is not in a matrix scenario he must also admit that he is not in a position to a priori tell if physicalism or dualism true. So, suppose that we are actually in a matrix scenario then conceiving of zombies is just conceiving of a computer simulation composed completely of NPCs (non-player characters). But this doesn’t show that physicalism is false, since physicalism is best construed as the claim that lines up with the first brain; since with this understanding of nonphysical physicalism turns out to be nothing but the hypothesis that we are not in the matrix.

But even if we were in the matrix there is a sense in which we can say that physicalism is still ultimately true since in the above envisioned world qualitative properties turn out to be identical to properties which are physical in terms of outside-physics (since these properties are the very same as the ones in the world where physicalism is true).

Zoombies are creatures that are nonphysically identical to me in every respect and which lack nonphysical qualitative properties. I have in the past suggested that one way to conceive of zoombies is as Cartesian minds that only have thoughts but no qualia but now we can put it in terms of matrix scenarios. A zoombie has all of the same nonphysical properties that I in fact do. Suppose that I am in fact in scenario 2 above. Then a creature that has all of the nonphysical properties that I in fact do will have a brain that is identical to my outside-brain. This is to imagine scenario 1.

The traditional zombie is a creature that is physically identical to me and lacks consciousness. Now suppose that I have a zombie twin who is in a matrix scenario since birth. My matrix zombie twin has nonphysical properties (which are the very same properties that I physically have) but no qualitative properties. So, whether one has nonphysical properties or not is simply a matter of whether one is in the matrix or not. Chalmers’ defense of nonphysicalism can thus be seen as a defense of the claim that we are in the matrix.

Kripke on the Structure of Possible Worlds

Yesterday I attended Saul Kripke’s talk at the Graduate Center (there are quite a few interesting talk coming up…also looking good are the cogsci talks). The title of the talk was “The Structure of Possible Worlds: a Preface to a statement” and was subtitled, “Prolegomena to a talk on possible worlds, some considerations” so maybe I didn’t really attend a talk. Much of the talk, um preface to a prolegomena to a talk, consisted of Kripke going over the history of his thinking on modality, punctuated with his usual wit and humor. My two favorite moments were (a) the one where, after talking for an hour (the scheduled length of the talk), he stops and says “I may have to go over because I haven’t come to the main point yet” and (b) the one where, while discussing modal realism, he says “what does God have to do to make a really existing merely possible world actual; give it a kiss?” Ah, that Kripke should have his own reality show…I bet it’d be really popular!

As to the content of the talk, or whatever, he seemed to be indicating that (he may have) changed his mind about how he conceives of possible worlds. Here is how he put it in the handout,

I used to think that a sufficient account of my view of what a possible world is might be given by something like a Russellian structured proposition describing it. Now i think that one cannot give an account of what a possible world is in and of itself, but only as part of the structure of all possible worlds, or at least that modal logic cannot rule this out. (Even if there is not a unique structure of all possible worlds, structures where the problem I have just described arise cannot be ruled out philosophically.)

A structured Russellian proposition is an abstract entity that has as its constituents the actual objects in the proposition. So, to modify the classic example, the proposition that Jennifer Aniston loves Brad Pitt has Jennifer Aniston (the actual person), Brad Pitt (the actual person), and the relation of loving as constituents and these constituents are ordered by the loving relation such that Jennifer loves Brad (which is a different ordering from Brad loving Jennifer). This is just a more refined way of putting the basic point of Naming and Necessity. When we ask if Al Gore could have won the election we are asking a question about the actual Al Gore. We are not talking about some distinct object which merely resembles Al Gore (or which merely has many of the same descriptions true of it). There is therefore no issue of how we re-identify Al Gore in various possible worlds; it is the actual Al Gore.

So why does he now think that we can’t do this? (Of course, he hasn’t really come to this conclusion officially. What he said was that it might be true and he sort of leaned towards thinking that it is true). The basic reasoning he employed relies on his argument that there can be objects which are indistinguishable in every way which are none the less distinct. There is no criterion of identity that distinguishes these objects; as Kripke put it “the only difference between them is that there is a difference.” His favorite example is the square root of -1, known as i. i is equal to whatever number equals -1 when multiplied by itself. This number is not on the real number line and so is known as an imaginary number. The problem comes when we realize that i and -i are distinct numbers and that everything that is true of the one is also true of the other. i and -i are distinct yet have no clear criterion of identity.

The problem that Kripke sees is that something like this might be true for possible worlds. To see this he talks about what he calls ‘grounded’ objects. So, let’s imagine a world where there is an person, let’s call him George, who does not exist in the actual world. Let’s say that George is the son of two people who actually exist but do not actually have kids. In the actual world the sperm and egg that come together to form George never meet, but they do in some possible world. So George is grounded in the actual gametes that he could be the product of. But there is also the possibility of ungrounded objects. So consider Georgette. Georgette is a women who does not exist in the actual world but does at some possible world, yet unlike George, Georgette is not the related to any past, present, or future actual person. The sperm and egg which come together to form Georgette at no time exist in the actual world; they are the products of an alternate history which does not overlap with the actual world (in this respect). Georgette is ungrounded.

So if there can be ungrounded entities then we can see that the following situation is possible. Imagine that there are two possible worlds each which has an extra hydrogen atom which is not related to anything that actually exists. These two extra hydrogen atoms are thus ungrounded. We can furthermore imagine that these two hydrogen atoms are indistinguishable from each other. Now if this is the case then the two possible worlds we are imagining are indistinguishable yet distinct. There is nothing that we could say about the possible world in and of itself that could distinguish between these two worlds. The only way that we could distinguish them is by noting their relative positions to each other in the overall space of possible worlds. Thus Kripke concludes that we cannot talk about individual possible worlds except in relation to the entire structure of modality, or to be more modest, he concludes that there is no a priori consideration that would rule this kind of automorphism out.

An interesting argument, and there is a lot more to say about it but I will come back to that later.

The Problem with 2-Dimensional Semantics

Central to the claim of Chalmers’ two dimensional semantics is the idea that there are two different ways of considering a possible world. We may consider it counter-factually in which case we hold the actual world fixed or we may consider as actual in which case the proposed possible world is thought of as being actual, with our world then a counter-factual world. Thus Twin Earth, considered as actual, is a world where water is not H20 but is rather XYZ. From their point of view it is a necessary truth that water=XYZ and so there would be no water here on Earth (considered counter-factually).

The problem with this line is that it assumes that we can tell a priori which possible worlds there are. Before we can consider a possible world as actual, we need to know whether it is possible or not. The two-dimensionalist simply asserts that some world is conceivable and then proposes to consider it as actual. But we have no non-question begging way of saying what is or is not really conceivable. Some claim that to be conceivable is simply to lack any contradiction in teh thing conceived. But just because there is no obvious contradiction in a proposed conceivable world does not mean that there is no contradiction in that coneption. Besides whihc, there are those who claim that contradictions are conceivable. Kripke famously proposed ‘non-normal’ worlds (sometimes called ‘impossible worlds’) these are worlds where contradiction are true or where standard laws of logic fail to apply (like the rule of necessitation). Are such worlds conceivable? Kripke seems to think so, others do not.

Until we resolve this issue two-dimensional semantics is hopelessly question begging. The only thing that we can consider as actual is, well, the actual world.