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.

11 thoughts on “Chappell on the A Priori

  1. Hi Richard, thanks for this interesting post!

    I’m worried, though, that you conflate two lines of criticism:

    (1) Disputing that an allegedly conceivable scenario is really (ideally) conceivable at all.

    (2) Disputing that ideal conceivability implies metaphysical possibility.

    Your square root example is not coherently conceivable. It may not be obviously false, but it is a priori false, or logically incoherent. We cannot conceive of any coherent scenario which would make it such that an actually false mathematical claim would instead be true. Similarly, I claim, for the meta-modal cases. These are all plain a priori logical impossibilities.

    My post on Kripke, however, addresses the very different problem of alleged a posteriori necessities. That is, they are cases (e.g. ‘water = XYZ’) which cannot be ruled out a priori. So they’re perfectly coherent.

    The Kripke/Putnam methodology involves imagining a world — a genuine metaphysical possibility — where the watery stuff is other than H2O, and then engaging in armchair reflection about how we should describe this world. By this armchair methodology, we come to the realization that we would never describe non-H2O watery stuff as “water”. So, we conclude that water is necessarily H2O. That’s how the Kripke/Putnam necessary a posteriori works. There’s no argument here against zombies, for the reasons I explain. (You might take a far more radical view, admittedly, but it finds no support from philosophical work in the tradition of Kripke and Putnam. I’ve never heard a philosopher suggest that Twin Earth is metaphysically impossible.)

    So, to clarify: my Kripke/Putnam post is not meant as a response to those who think that zombies are a priori incoherent, the way that mathematical falsehoods are. I don’t address that view at all. (Does anyone apart from Dennett seriously believe such a thing?) I’m instead addressing the far more common #2-type criticism.

  2. To me the whole spiel of “modal logic”, “ontological arguments”, “contingency” and “possible worlds” is suspect as a whole. What we have to keep in mind is that possible worlds, and logic, and are simply structured though-games of the people who make them up.

    Like that, the ontologial argument for God is essentially for me a cloaked way to say: “We can think of a being (God) that must exist in all worlds and we can also think of a world in which it does exist, so, that being must also exist in our world.” Well, yes, it does, but only in our thoughts! Basically what’s the problem is an insidious equivocation falacy where “nessecarily existence as it is used modal logic” which is a purely theoretical concept, is conflated with “existence in our world”, which is must be tested empyrically. Those two concepts are very different!

    Math, and also logic are in essence a collection of games, each limited by a set of rules (axioms). These rules have implications (theorems) that will limit what is possible in each of those game.

    In standard 5 card poker it’s a nessecary truth that you can’t have two pairs and a 5 card straight flush. But if I invent my on kind of poker, say with 9 cards, then such a combination would be possible. Likewise, in Euclidian geometry square cicles with finite nonzero radius are not possible, but this is hardly “nessecarily” so in all kinds of maths se non-eulidian geometry). And I could construct a system of logic that alows contradictory statements to be true (admitting that it would be useless in our world).

    Of course, we invent and use the kinds of math and logic that are most useful to us first and foremost, but that is only due to the properties of the real world we live in, and the way we generaly experience it. Our world seems consistent, so we require noncontradiction from logic. In our worls 2+2=4 so we require that from our math, etc, etc. But not all things are what they seem!

    All form of ontological proofs are in essence trivial deductions from the axioms. The main question always remains whether the game we are playing and it’s rules are applicable to our wold, to reality or not. That can only be demonstrated empyrically.

  3. Thanks for the response Richard.

    I think I see what is going on here. You are right that in the Twin Earth case people do take themselves to be thinking about a genuine metaphysical possibility where the watery-stuff isn’t H2O and the question is then whether or not to call that watery-stuff ‘water’. I din’t mean to suggest that Twin Earth was metaphysically impossible, though I don’t see anything wrong with that view.

    You then claim that the same thing is happening in the zombie world cases, and this is what I am disputing. So, as I said, IF we are really entertaining something which is ideally conceivable then that thing is metaphysically possible (I don’t think that Kripke disputes this). What is disputed is that some seemingly conceivable worlds are really conceivable. This was part of Kripke’s strategy in explaining the necessity of identites. It seems as though we are thinking about a world where there is water and no H2O (or where Hesperous is not Phospherous) but we are really thinking about a world where stuff that looks like water isn’t H2O (not where THIS STUFF, pointing to some H2O, isn’t H2O).

    The ani-zombist makes the same claim about the zombie world. It seems as though we are thinking of a coherent world where there are physical creatures just like us and yet lacking consciousness, but we aren’t. No such world is (metaphysically) possible or coherently concievable. There are plenty of philosophers who argue this way (John Perry and Robert Kirk spring to mind).

    If there is something wrong with this (what I take to be quite standard) response to the zombie argument, then there is something wrong with your defense of modal rationalism, since you adopt the very same strategy.

    Hi Beoran,

    I have a lot of sympathy with what you say here.

  4. I think you’re still confusing the dialectic, by failing to adequately distinguish the two lines of objection I highlighted for you. (These correspond to Type-A and Type-B materialism, respectively.)

    Here’s the key point: in the Kripke/Putnam cases, when it *seems* to us that we’re imagining “a world where there is water and no H2O”, in fact we are imagining a slightly different world – the Twin Earth one – where the watery stuff (the stuff that plays the ‘water’ role) is not actually water. There is a genuine possible world here, it’s just that we may initially misdescribe it if we’re not careful. Note that this is a type-2 criticism, because nobody thinks ‘water = XYZ’ is a priori incoherent.

    If the anti-zombist “makes the same claim about the zombie world”, then they are granting the a priori coherence of the concept. We can then expect that there is a genuinely possible world in this vicinity (again, on the analogy to Twin Earth), it’s just that the phenomenal stuff that’s missing from this world isn’t the same as our actual phenomenal properties. I explain in my post why this suffices to refute physicalism all the same.

    Now, it simply isn’t true that I “adopt the very same strategy” in my opposition to meta-modal conceivability claims. I think they’re simply a priori false — not a priori coherent at all. This is a type-1 criticism. So the fact that I think type-2 criticisms are invalid does not undermine my own use of type-1 criticisms.

    You could make a type-1 criticism of zombies too, and insist that they are likewise a priori incoherent. Type-A materialists like Dennett believe this, but I don’t believe this is the “standard” response, and it’s certainly nothing at all to do with the Kripkean necessary a posteriori. Anyway, like I said, I don’t offer any argument against this view. (No more than I bother to argue against radical skeptics in any other area. If they offer some specific grounds for skepticism in a particular case, then I’ll pay attention. But I haven’t seen any reason to think that zombies are incoherent.)

    You write: “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

    That sounds excessively skeptical to me. If something seems coherently conceivable, then the burden is on those who would deny this intuition. Just as we can show that the square root case leads to a contradiction — and just as I gave reasons to think that the meta-modal cases are not genuinely conceivable — so the Type-A materialist, if they want to offer a type-1 criticism, must provide some reasons to back it up. That is, I would need to see some reasons to believe their claim that the zombie concept contains an implicit contradiction. *IF* they can provide such reasons, then sure, that’d support physicalism. But a hypothetical argument is not yet an argument.

  5. That’s funny, I thought you were confusing the dialectic! (by the way, who is the dialectic and why is he confused?) 😉

    “Here’s the key point: in the Kripke/Putnam cases, when it *seems* to us that we’re imagining “a world where there is water and no H2O”, in fact we are imagining a slightly different world “

    Yes, that is the key point I was trying to get at as well. The typical response to the zombie argument is exactly the same response. It seems to you as though you are imagining a world with creatures like us and no qualitative consciousness but you are not. You are instead imagining a slightly different world.

    You want to focus on the claim about ‘the genuine possibility of Twin Earth’ whereas I am focusing on the claim about the seeming concievability of water not being H2O. The Kripke cases start from the fact that something *seems* imaginable to us and then argues that it really isn’t. The anti-zombist insists that the zombie world is not *really* concievable; whether the evidence for that is a priori or a posteriori seems irrelevent to me. Why should it matter where the evidence for the inconceivability comes from? If it is inconcievable then it is inconcievable, and so not metaphysically possible (on your view); what’s the difference if we learn that from reason or from experience?

    Re the type-1 and 2 distinction, Kripke has never denied (as far as I know) that concievability entails possibility. Twin Earth is concievable and so is a metaphysical possibility, but that is not a world where (this stuff) pointing-at-some-water-here-in-my-room-on-Earth is not H2O. That is a world where there is stuff that looks like (this stuff) which isn’t H2O. What he denies is that we are really concieving of the things that we think we are concieving (and this is what the typical anti-zombist claims). Why else would he think he has an argument for dualism himself? He argues from the conceivability of pain existing without brains to the conclusion that materialism is false (as I have said though, this line of argument begs the question becasuse a case can be made that it is perfectly concievable that there might be a pain which wasn’t painful or something painful which wasn’t a pain…in fact it may be actual!!).

    In this sense you do adopt the same strategy. What you in effect argue is that the space of epistemic possibilites must be pruned down to the space of metaphysically possible ones and in that sense you do the same thing that you complain about. It is just that you think the evidence comes from reasoning about what is possible.

    “If something seems coherently conceivable, then the burden is on those who would deny this intuition. Just as we can show that the square root case leads to a contradiction”

    I agree with this, and so does teh anti-zombist (and this is just what Kripke does as well). In the zombie case there have been a couple of attemots to articulate the argument that the zombie world is contradictory. One is John Perry in “Knowledge, Possibility, and Consciousness”, the other is Robert Kirk in ‘Zombies and Consciousness’ (you can see my review of this for phil. psych. in the side bar for a quick summary of the arg. if you are interested)Perry argues that the zombie world isn’t really concievable because it entails epiphenominalism and epiphenominalism is false (though he disputes that the zombie world has anything to do with dualism. A dualist who thought that the non-physical states of consciousness interacted with the physical would also have to say that the zombie world is inconcievable, because it is to imagine a world just like ours except missing a bunch of causes and it is contradictory to think that such a world would be indistinuishable from ours. How could you have all the same effects without the same causes?)

    So the way you characterize the dispute as between type-1 and type-2 crisisms is misguided. Who are these people who give type-2 cristisims? No materialist I have heard of admits that the zombie world is a genuine metaphysical possibility or that it is genuinely concievable (if they did then you would be right about them). They all say ‘it *seems* like it is, but really it isn’t’ and you are right that you haven’t offered any arguments against this response to the zombie argument.

  6. We are conflating various senses of ‘conceivable’ here. That’s my fault for wording my last comment badly.

    It’s perfectly conceivable – in the sense of not a priori false – that water is XYZ. This means there’s a genuinely possible world (Twin Earth) where the semantically neutral analogue of this claim, viz. ‘the watery stuff is XYZ’, is true. (Put yet another way, the conditional ‘if Twin Earth is actual then water is XYZ’ is a priori.)

    Note that we are in no way mistaken about the qualitative nature of the possible world we’re imagining here. So there is no generally accepted counterexample to the claim that any semantically neutral (e.g. purely qualitative) claim is metaphysically impossible iff it can be ruled out a priori.

    [This is the thesis of Modal Rationalism: for any semantically neutral claim P that cannot be ruled out a priori, P is possible.]

    But the zombie claim is (arguably) purely qualitative. So it should be metaphysically impossible iff it can be ruled out a priori (i.e. via type 1 criticism). But few people think that it can. Most – e.g. Block, Yablo, Loar, Chris Hill, even Perry I think – grant that zombies are a priori coherent and instead deny that their metaphysical possibility follows from this. That is, they must deny Modal Rationalism and engage in type-2 criticism.

    Even if you deny that the zombie claim is semantically neutral, you must grant that there is a “nearby world” we are imagining (as in the twin earth case), where its semantically neutral analogue is true. And that world will be enough to refute physicalism. (As before, the world is such as to ground the conditional, ‘if this world is actual then there are zombies’. Any world of such a qualitative nature is clearly enough to refute physicalism!)

    Anyway, I’m a bit tired and not expressing myself very clearly, I’m afraid. I’ve tried to avoid the technicalities of 2-D semantics, though I think it’s actually pretty vital for getting clear on the issues. (E.g. if it isn’t clear to you why the various claims I’m calling ‘equivalent’ really are equivalent.) But, as you know, I’ve a whole thesis on this stuff, and it would be a bit silly to try and reproduce it all here in a blog comment. So I’m afraid I’m just going to have to leave you with the lazy injunction, “follow the link for a full explanation”. Sorry.

    However, I do want to reiterate the two main points I have in response to your post:

    (1) I *do* argue against type-B materialists, i.e. those who grant that zombies cannot be ruled out a priori. That’s most philosophers.

    (2) Contrary to your suggestion, those arguments cannot be turned against me, because they vitally rest on the a priori coherence of the possibility claim in question, and the meta-modal claims I rule out as impossible are not claims that I grant as a priori coherent.

  7. “But the zombie claim is (arguably) purely qualitative.”

    This is actually what is in dispute. The claim is that it only seems to you as though you are imagining the zombie world. The zombie world is NOT like Twin Earth, it is like the world where Hesperous is not Phoserous (that is it is really a world where the contingent property that we here on Earth use to pick out Venus picks out some planet other than Venus).

    “Even if you deny that the zombie claim is semantically neutral, you must grant that there is a “nearby world” we are imagining (as in the twin earth case), where its semantically neutral analogue is true. And that world will be enough to refute physicalism. (As before, the world is such as to ground the conditional, ‘if this world is actual then there are zombies’. Any world of such a qualitative nature is clearly enough to refute physicalism!)

    Why must anyone grant that? In the water H2O case it is not the case that we are imagining a world where water is not H2O, we are really imagining a world where there is stuff that looks like water does to us which isn’t H2O, so in the zombie world case the same is true. We are not imagining a world that is physically identical to the actual world and in which there are no conscious mental states; we are in fact imagining a world that looks an awful lot like it is physically idenitcal to the actual world (but isn’t) and in which there are no conscious mental states. How can that world be a threat to physicalism? It can’t be! It has been a while since I really read Perry, but that’s pretty much his argument as I recall it. I can’t say very much about the rest on the list; perhaps you do have a point against them, but your argument does nothing to a physicalist like Perry.

    “Contrary to your suggestion, those arguments cannot be turned against me, because they vitally rest on the a priori coherence of the possibility claim in question, and the meta-modal claims I rule out as impossible are not claims that I grant as a priori coherent.”

    I guess I’ll just try to restate the case. I think you may still be slightly missing my point. So, the Kripkean thinks that what is actually conceivable a priori (in you sense) falls short of what is really conceivable a priori. You objection to this, I take it, is that it denies things that seem like real possibilities. Instead, we see the speace of possibilities as set qualitatively and what is open for debate is how we define the terms we are employing. But then, later when you are defending modal rationalism from the charge of internal inconsitency, you make exactly the same move. You argue that there are worlds that seem possible which aren’t. Why is it that it is ok to shrink modal space for your view but not for the Kripkean? I presume that your answer is that we can rule it out a priori that there are no qualitatively identical worlds in which the relevent counter-factuals would be true (i.e. ‘if this world we actual there would be a necessary being). In the case of the Kripkean we rule this out not on the basis of a priori reflection but on the discovery of contingent truths about the actual world. Im both cases we are shrinking the space of what is really possible and so concievable.

  8. Just to be clear; I am NOT suggesting that you are really imagining a genuinely possible world where there is (say) a necessary being in your defense of CT. I understand that you deny that such a world is a priori concievable and so you do not fall intot the trap that you think the Kripkeans do.

    What I AM suggesting is (A) The Kripkean (needn’t) fall into that trap either since you misdescribe their strategy and (B) Your defense of CT ends up ‘shrinking’ modal space in the exact same way that the Kripkean (actually) does (from seemingly concievable to inconceivable).

  9. […] I have been arguing that Chappell’s argument fails to address the most plausible physicalist response to the zombie argument (and that his defense of modal rationalism itself adopts a version of the Kripkean strategy). This is to deny that the zombie world is actually conceivable. Sure, it seems to Chappell that he is imagining a world where there are physical duplicates of me (or you) and no consciousness but he is really imagining a world that LOOKS a lot like there are physical duplicates of me (or you) which lack consciousness. This is what I have been calling the Kripkean response because it is exactly the strategy that Kripke adopts in Naming and Necessity. It seemed to people that they were imagining a world where water wasn’t H2O (or where Aristotle wasn’t Aristotle) but they are really imagining a world where there is stuff that LOOKS like water does to us which isn’t H2O (or a world where there is a person who LOOKS like Aristotle (or satisfies most or all of the descriptions that Aristotle satisfies in the actual world) who isn’t Aristotle). Why should we think this is really what is going on? There are many reasons: […]

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