The Argument for Simulation via Traditional A Posterori Arguments for God’s Existence

I had a fun and interesting discussion with Canadian Catholic on his Global Skeptics podcast the other day. In the course of our discussion something clicked that has been loosely kicking around in the back of my mind. I have previously suggested that the argument from design is an argument for simulation and that the problem of evil is made much worse when thinking about why humans aren’t photosynthetic. I now think there is a general argument here.

  1. The traditional A Posteriori arguments (Cosmological, Teleological, etc) point, if one accepts their conclusions, to a creator but *not* to what kind of creator
  2. The traditional theistic God (all-powerful, all-knowing, and morally perfect) is one candidate for being the Creator
  3. The Simulators are another candidate
  4. The traditional arguments do not distinguish between (2) and (3)
  5. The problem of evil (evidential) suggests that 2 is not the creator [especially the version emphasizing photosynthesis]
  6. Therefore, the traditional arguments for God’s existence provide better support for the simulation hypothesis than they do for the traditional God of Theism

What do you think? I could formalize it up a bit but I think I kind of like it!

Zombies vs Shombies

Richard Marshall, a writer for 3am Magazine, has been interviewing philosophers. After interviewing a long list of distinguished philosophers, including Peter Carruthers, Josh Knobe, Brian Leiter, Alex Rosenberg, Eric Schwitzgebel, Jason Stanley, Alfred Mele, Graham Priest, Kit Fine, Patricia Churchland, Eric Olson, Michael Lynch, Pete Mandik, Eddy Nahmais, J.C. Beal, Sarah Sawyer, Gila Sher, Cecile Fabre, Christine Korsgaard, among others, they seem to be scraping the bottom of the barrel, since they just published my interview. I had a great time engaging in some Existential Psychoanalysis of myself!

The 2D Argument Against Non-Materialism

On wednesday I gave my talk out here in Tucson. You can see a rehearsal of it below. The discussion was very interesting and I thought I would quickly jot down a few notes on what happened.

Right at about 1:00 minute into the talk Dave Chalmers spontaneously objected to the way that I had formalized the shombie argument, which I reproduce here for ease of reference.

1. (~p v q) is conceivable
2. If it is conceivable then it is possible
3. if it is possible then non-materialism is false

In short his objection was that (~p v q) isn’t the right way to formalize the first premise of the argument. He had two related points to make. The first contention was that I needed a modal operator to capture the tension between the physicalist and the non-materialist. So, I would need something like [](~p v q) (which is equivalent to ~<>(p & ~ q)). But of course I do not want to do this at all! That would make premise one totally inconceivable. I really do not think I am able to conceive of the entire space of possible worlds and see that this is true in each of them. In fact Dave makes much the same point in his 2D argument against Materialism paper against a similar move made by Yablo. All that is needed in premise one is that it is conceivable that consciousness is physical at one possible world, not all of them!

This brings up his second objection, which was that (~p v q) is conceivable but in a way that doesn’t license the inference in premise three. So, one can easily conceive of someone being conscious, and so conceive of that person being conscious or our physics being false. But this misses the point of premise one. It is not merely that (~p v q) is conceivable. Rather the claim is that I can conceive of this being true of my physical duplicate. Since we know that ~p is false at this world (we are considering a physical duplicate of me in a world that duplicates our completed physics so p must be true) it has to be the case that q is true. That is just to say that this physical duplicate of me has consciousness in just the way that I do. What is key here is that this world merely duplicates our completed physics. So, it is no good to object that this would be true in a world where there are Cartesian spirits plus our physics (as David Pitt did). That world has more in it than our physics but the shombie world, and hence my shombie twin, has just our physics.

Given all of this premise one should perhaps be re-worded as 1′.

1′. A mere physical duplicate of me, of which (~p v q) is true, is conceivable

But of course I do agree that physicalism is the thesis which holds [](p –> q). The only point I have been making above is that I do not need to include the modal operator in the first premise, which is a premise about what is conceivable. I do not need to conceive of a necessary truth in order to conceive of a shombie: that is the crucial point. The necessity comes from an independent argument that identities, if true, are necessarily true. This is the role that Kripke’s argument is playing. It is that argument which should convince us that it is necessary that the physical facts entail the qualitative facts. Given this I should probably state the third premise as 3′.

3′. If shombies are possible then, if identities are necessary then non-materialism is false.

So, summing up, we can state the more explicit 2D argument against non-materialism as follows.

1′. A mere physical duplicate of me, of which (~p v q) is true, is conceivable
2. If it is conceivable then it is possible
3′ If it is possible then, if identities are necessary then non-materialism is false.
4. identities, if true, are necessarily true
5. Non-Materialism is false

There is more that I want to say (and more interesting questions and issues raised in the discussion) but I will have to come back to it later.

Clip Show ‘011

It’s that time of year again! Here are the top posts of 2011 (see last year’s clip show and the best of all time)

–Runner Up– News Flash: Philosophy Sucks!

Philosophy is unavoidable; that is part of why it sucks!

10. Epiphenomenalism and Russellian Monism

Is Russellian Monism committed to epiphenomenalism about consciousness? Dave Chalmers argues that it is not.

9. Bennett on Non-Reductive Physicalism

Karen Bennett argues that the causal exclusion argument provides an argument for physicalism and that non-reductive physicalism is not ruled out by it. I argue that she is wrong and that the causal exclusion argument does cut against non-reductive physicalism.

8. The Zombie Argument Requires Phenomenal Transparency

Chalmers argues that the zombie argument goes through even without an appeal to the claim that the primary and secondary intension of ‘consciousness’ coincide. I argue that it doesn’t. Without an appeal to transparency we cannot secure the first premise of the zombie argument.

7. The Problem of Zombie Minds

Does conceiving of zombies require that we be able to know that zombies lack consciousness? It seems like we can’t know this so there may be a problem conceiving of zombies. I came to be convinced that this isn’t quite right, but still a good post (plus I think we can use the response here in a way that helps the physicalist who wants to say that the truth of physicalism is conceivable…more on that later, though)

6. Stazicker on Attention and Mental Paint

Can we have phenomenology that is indeterminate? James Stazicker thinks so.

5. Consciousness Studies in 1000 words (more) or less

I was asked to write a short piece highlighting some of the major figures and debates in the philosophical study of consciousness for an intro textbook. This is what I came up with

4. Cohen and Dennett’s Perfect Experiment

Dennett’s response to the overflow argument and why I think it isn’t very good

3. My Musical Autobiography

This was big year for me in that I came into possession of some long-lost recordings of my death metal band from the 1990’s as well as some pictures. This prompted me to write up a brief autobiography of my musical ‘career’

2. You might be a Philosopher

A collection of philosophical jokes that I wrote plus some others that were prompted by mine.

1. Phenomenally HOT

Some reflections on Ned Block and Jake Berger’s response to my claim that higher-order thoughts just are phenomenal consciousness

Applied Mathematics and Scrutability

Also via Leiter’s blog I was perusing the Philosopher’s Annual list of the ten best papers of 2008. The paper on Mill is very interesting and I have heard a lot about belief and alief lately but what really caught my attention is Penelope Maddy’s How Applied Mathematics Became Pure.

The whole paper is really very interesting and I would highly recommend that you read the whole thing but I want to quickly discuss one of the morals that she draws from the story she tells. She says,

This story has morals, it seems to me, about how mathematics functions both in application and in its pure pursuit. One clear moral for our understanding of mathematics in application is that we are not in fact uncovering the underlying mathematical structures realized in the world; rather, we are constructing abstract mathematical models and trying our best to make true assertions about the ways in which they do and do not correspond to the physical facts. There are rare cases where this correspondence is something like isomorphism – we have touched on elementary arithmetic and the simple combinatorics of beginning statistical mechanics, and there are probably others, like the use of finite group theory to describe simple symmetries – but most of the time, the correspondence is something more complex, and all too often, it is something we simply do not yet understand: we do not know the small-scale structure of space-time or the physical structures that underlie quantum mechanics. And even this leaves out the additional approximations and accommodations required to move from the initial mathematical model to actual predictions.

I wonder if this is right if it causes problems for the kinds of scrutability claims that David Chalmers wants to defend, and which for the most part I am highly sympathetic to (of course where we differ is over whether we need to include phenomenal truths in the base truths or not…I think probably not since they can be derived just as easily as other ordinary macroscopic truths).

The problem, it seems to me, is that if this is right (i.e. if at the limit we do not end up with a unified mathematical model of the world but rather patchwork models that apply only in various respects) then which mathematical model we apply or assumption we make will crucially depend on empirical knowledge (for instance knowing that the equations for a harmonic oscillator  are a good model of a molecule’s vibration only in the region of the minimum (see page 35)). Am I missing an easy response?

I’ll have to think about it later because now I’m off to Jared Blank’s cogsci talk

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 |

Pain Asymbolia and A Priori Defeasibility

I listened to the first lecture in David Chalmers’ Locke Lectures currently taking place at Oxford and I was intrigued by the argument he gave in defense of the claim that we can have a priori knowledge and do conceptual analysis even if we cannot give definitions of the concepts that we are analyzing. The argument appealed to the claim that any counter-example to a definition involved reasoning about possible cases and so we could give an account of the a priori in terms of our capacity to think about possible scenarios and our judgments about whether certain sentences are true in those scenarios.

I wanted to find the text of the talk to check on the details of the argument and in the lecure Dave mentioend that he was putting manuscripts up online and I went to his website to see if I could find them…sadly I couldn’t. But I did find this paper which if I am right is probably the text that the fourth lecture will center on. Anyways, I read the paper and now want to say something about it. As I read it the central point is very simple: one can accept Quinian arguments about conceptual revisibility and still have a robust a priori/a posteriori and analytic/synthetic distinction.  One does this by simply stipulating that something is a priori if it is knowable independently of experience without conceptual change. That is given that we hold the conceptual meanings fixed is the statement knowable a priori? Much of the paper is spent fleshing out a suggestion made by Carnap updated with 2-d semantics and Bayesian probability theory aimed at giving an account of conceptual change.

So to put it overly simply one can say to Quine “sure, my concept may change and if so this wouldn’t be true but given that my concepts don’t change we can see that this would be the case.” So to take pain as an example. When we are reasoning a priori about what we would say about pain (can there be pain/pleasure inversion for instance) we can admit that if we change what we mean by pain this or that will be different. But as long as our concept of pain doesn’t change we can say this or that would be true in this or that scenario and therefore bypass the entire Quinian argument altogether. This would seem to give Dave a response to the type-q materialist who has been getting so much attention around here lately. This is because they seem to be saying that since our concept of pain might change we cannot know a priori whether zombies are conscious or not. Dave responds by saying that as long as we do not have to change our concept of pain we can see that zombies are not conscious. I think that this response to the Quinian argument is quite good but I would respond to it differently. I would argue that as of right now we do not know which scenarios are ideally conceivable because we have cases of disagreement about decisive scenarios.

To fill this in with a particular example that I have talked about before let us focus on the notion of pain and Pain Asymbolia. Now many philosophers hold that it is a priori that if something is a pain then it will be painful (and that conversely if something is painful then it will be a pain). Now suppose that one of these philosophers finds out about pain asymbolia and denies that these people are in pain. Now suppose that this person comes to change their mind and instead thinks that they are in pain but that pain and painfulness are (contrary to appearances) only contingently related. What are we to say? In the paper Dave says,

A fifth issue is the worry that subjects might change their mind about a possible case without a change of meaning. Here, one can respond by requiring, as above, that the specifications of a scenario are rich enough that judgments about the scenario are determined by its specification and by ideal reasoning. If so, then if the subject is given such a specification and is reasoning ideally throughout, then there will not be room for them to change their mind in this way. Changes of mind about a fully specified scenario will always involve either a failure of ideal reasoning or a change in meaning.

I can agree with this in principle but since I can clearly conceive pain and painfulness being only contingently related it cannot be the case that we are in a position to determine which concept of pain is the one which will be employed in ideal reasoning. We may have our favorite but there are arguments on both sides and it is not clear where the truth lies. So though we can know a priori that either pain is necessarily painful or that it is contingently painful but we cannot know which is true now. To know that we would have to settle the pain asymbolia case; but that case it hotly contested (pun sadly intended :()

The upshot then is whether or not Dave has a response to Quinian worries about the a priori in principle he has not done enough to show that we are currently in a position to make use of this apparatus and so we are forbidden any of its fruits.

Empiricism and A Priori Justification

I sometimes get asked why I take a priori reasoning seriously; after all empiricists should eschew such talk! Real empiricists do not engage the rationalist on their own turf…in true Type-Q style I should deny that there is an a priori/a posteriori or an analytic/synthetic distinction and deny as well that talk of possible worlds is meaningful. But I don’t.

Let us define A Priori knowledge as follows

APK=def justified necessarily true belief

Let us define A Priori justification as follows

APJ=def justification that is not based on experience (i.e. not based on sensing, perception, memory or introspection)

A Priori justification usually takes the form of a ‘rational seeming’ which phenomenologically is a kind of ‘seeing’ that something could or couldn’t be the case. One has an immediate intuition that the proposition couldn’t possibly be true (or false). So, for example, when I consider simple propositions like that A=A, ((P–>Q) & P) –>Q, and (P v ~P) <–> ~(P & ~P) I find it unimaginable that they could be false.  It is this phenomenology which leads people to argue along the lines of ++

++   APJ –> APK

Since it seems to one unimaginable that P is false (or true) one concludes that it must be true (i.e. that it is necessarily true). It is also taken to be the case that the history of philosophy has demonstrated that experience cannot teach that something is necessary and so APJ is the only route to APK.

Now as an empiricist I want to deny that we have a priori knowledge but I want to allow there to be a priori justification. In other words I want to allow that rational seemings can provide justification even though they don’t provide (necessary) knowledge this is because rational seemings are, according to me, ultimately themselves dependent on how the world turns out. Suppose for the sake of argument that the above simple propositions are not in fact necessarily true. Suppose that they are just extremely well confirmed empirical generalizations. That is, suppose that the regularities of our Humean world regularly, and up until now reliably, provide us the kinds of experiences that justify instances of these propositions. Suppose further that you have organisms evolving in this environment. These organisms will likely develop systems that encapsulate these propositions. To these organisms these propositions will seem to be unimaginably false (or true) but they are not necessary truths (ex hypothesi) and they are ultimately justified by the organism’s ancestor’s experiences. But these propositions are true; it’s just that they aren’t necessarily true. So one can have knowledge that has a priori justification but that is not a priori knowledge. Now I am not here trying to give an argument for this view. I only mean to be pointing out that this is perfectly compatible with the empiricist view and so if one is careful one can be an empiricist and still think that we can have knowledge on the basis of a priori reasoning.

So far I have been only talking about knowledge of how the world actually is. Nothing has been said about the way it could be. reasoning about modality seems to me to be fundamentally rooted in our ability to imagine or conceive of various situations. Conceivability has traditionally thought to be a guide to what is possible and to be bounded only by what is contradictory. That this be true is certainly conceivable (just as is the empiricist version above). We may not know that it is true but it does seem like a possibility. So, for instance, it is almost impossible to see what it could even mean to say that [](A=A) is false…I mean that would have to mean that there was some thing picked out by ‘A’ which was identical to itself in some conceivable situations but was not identical to itself in other conceivable situations. That just intuitively seems contradictory! But, wait, we can have rational seemings in the absence of necessary truth. So, famously, when some people offered “proofs” of the parallel  postulate they were accepted as correct until some mistake in the proof was discovered. If so, then there was a time when people could have a priori justification for something which turns out to be demonstrably false. So perhaps our intuition that justifies our belief in [](A=A) and the like are also suspect. As a counter example David Rosenthal talks about identity statements like [](A=A) beg the question by assuming the notion of rigid designation. If one doesn’t assume that it is of course not necessary. But it seems to me that the 2-D response has legs here: we can have both. Intuitions about rigidity are explained by the secondary intension and the corresponding kinds of possibility. Intuitions about the non-necessity of identities are explained by the primary intension and the corresponding kind of possibility. In short then as long as we see rational intuition as defeasible justification (defeasible in particular by experience) then we can accept the a priori justification of [](A=A) in the absence of defeaters which we have yet to find anyway

To sum up then; I think I can know that for any A,  A=A a priori but not that [](A=A) yet even so I think that I have good justification for believing [](A=A) and []~(P & ~P) and so we have good justification of modal talk.

Top 10 Posts of 2008

OK, so the year isn’t over yet…but these are the most view posts so far…

–Runner up– Reverse Zombies, Dualism, and Reduction

10. Question Begging Thought Experiments

9. Ontological Arguments

8. The Inconceivability of Zombies

7. There’s Something About Jerry 

6. Pain Asymbolia and Higher-Order Theories of consciousness

5.  Philosophical Trends

4. A Short Argument that there is no God

3. Has Idealism Been Refuted?

2. God versus the Delayed Choice Quantuum Eraser

1. A Simple Argument Against Berkeley

Chappell on the A Priori

The a priori seems to be on the rise of late, especially with defenders like Richard Chappell championing the cause. According to Chappell an ideallly rational being would have access to all the metaphysical possibilites. Given that we can ideally (or coherently)  conceive something we can infer that the thing in question is metaphysically possible. This is, of course, the basis for the zombie argument against materialism. Since we can coherently concieve of a zombie world (a world where there are beings like us in every physical way except that they lack conscious experience) that shows that consciousness cannot be a physical property.

The standard (Kripkean) objection to this line of argument is to try to distinguish between metaphysical and epistemic possibility. Some things that are epistemically possible (i.e. seem coherently conceivable) turn out to be impossible (a classic example is to point out that before you learn that the square root of 1,987,690.000 is 1409.855 (rounded up to the nearest thousandth) it is concievable that it be other than 1409.855 but once we find out what it is it is impossible for it to be otherwise. According to the materialist one of these things is the zombie world. While it seems that we can coherently concieve of such a world, we are actually missing some contradiction, or physical difference between our world and the zombie world and so it is not actually (ideally/coherently) concievable. 

Chappell objects to this line of argument for (at least) two reasons. The first has to do with the theoretical extravagance of the materialist’s claim that the identity between (say) H2O and water is necessary. It posits an unexplained strong necessity, wheras the modal rationalist (the one who thinks that it is a metaphysical possibility that water could be other than H2O, not just an epistemic possibility) doesn’t have to posit something like this. All that she needs to posit is a single uniform space of possibilities that we describe in various ways. The materialist has to posit a space of epistemically possible worlds and a seperate space of metaphysically possible worlds. Parsimony and simplicity seem to favore that modal rationalist here.

The second is an attack on the claim that calling something a rigid designator settles the dispute. As Chappell says,

Perhaps our term ‘consciousness’ is, like ‘water’, a rigid designator. But who cares about the words? Twin Earth still contains watery stuff, even if we refuse to call it ‘water’, and the Zombie World still lacks phenomenal stuff (qualia), even if we stipulate that our term ‘consciousness’ refers to some neurophysical property (and so is guaranteed to exist in this physically identical world).

Yes it will, IF we have settled the issue in favor of Chapell’s view and we then think that we are genuinely concieving of a real metaphysical possibility. If there is a question as to whether these kinds of possibility are distinct then Chapell has done nothing more than beg the question.

This is evidenced when he says,

Kripke himself noticed something along these lines. While we can imagine a world where watery stuff isn’t truly water, it’s incoherent to imagine a world where “painy” stuff isn’t truly pain. To feel painful is to be painful.

Pointing out that Kripke begs the same queston as you are beging is not a way to absolve yourself of beging the question. There is a legitimate case to made that being in pain and feeling pain are in fact two seperate things. The evidence for this comes, not from a priori reflection on the nature of pain, but from evidence from cognitive science.

 But suppose that you are not moved by this evidence and you still maintain that a priori analysis reveals that the zombie world is metaphysically (not just epistemically) possible. Is this a coherent position? One objection that immediately pops up is that on this view it seems that we can concieve of various possible worlds that result in contradiction. So, I seem to be able to concieve that God necessarily exists and that God necessarily doesn’t exist (or that numbers do and don’t necessarily exist). Since the claim that conceiveability entails possibility entails that God (or numbers) both necessarily exists and doesn’t exist only one of those possibilities can be a real metaphysical possibility; the other must be an epistemic possibility.

Chappell is of course aware of this objection and tries to deal with it in the post linked to above. Here is what he says,

I agree with Chalmers that the most attractive response for the modal rationalist here is to hold on to their strong position, and instead deny the… conceivability intuitions found, for example,…above. It isn’t at all clear that a necessary being, or a shrunken modal space, is coherently conceivable in the appropriate sense. The modal rationalist will want to hold that their position is not just true, but a priori. They would then expect opposing views to be refutable a priori, and hence not feature in any a priori coherent scenario. Of course, it would beg the question to merely assert: “the thesis is true and hence has no successful counterexamples”. But that is not what’s going on here. Rather, I hope to show that the modal rationalist can explicate their commitments in a way which makes clear exactly why, on their view, the meta-modal cases in question are not taken to be genuinely conceivable. If successful, this should suffice to undermine the charge of internal inconsistency or self-refutation.

The problem with this line of argument is that it commits the very ‘fallacy’ that Chappell accuses the Kripkeans of making. The strategy that he is here proposing is that of trying to show that there is some possible state of affairs that seems conceivable but which, on reflection, is not in fact metaphysically possible (i.e. that there are possibilities that (seem)concievable but are not metaphysically possible). But if there are possibilities that (seem) concievable but not metaphysically possible then we need an independent argument that the zombie world is not one of these worlds. No such argument has been given. Rather what Chappell does is to assume that it is in fact coherently concievable; but this cannot be assumed if there are any possibilities which (seem) concievable and are not metaphysically possible. Chappell’s own view commits him to there being such possibilites, so by his own view the modal argument against materialism is suspect.