Conceivably possible zombies

Does the conceivability of zombies threaten type-A materialism, the claim that all mental truths are a priori entailed by the physical truths?

We can imagine beings exactly like us in all physical respects, but lacking consciousness. But this doesn't threaten type-A materialism (as I mentioned here). After all, it isn't a priori that materialism is true. It could have turned out that ectoplasmic states, rather than brain states, occupy the causal roles that, by analytic necessity, belong to mental states. Suppose it turned out that way. Then duplicating only our physical constitution would result in a being that is physically just like us, but lacking consciousness. So by type-A materialist lights, it is conceivable that things are such that there are beings physically just like us without consciousness.

The same holds for the conceivability of a consciousness-free world that is a complete physical duplicate of the actual world: type-A materialism can accept that.

Next, let P be the conjunction of all physical truths, and Q a mental truth, say, "there are conscious beings". Type-A materialism claims that "if P then Q" is a priori. But can't we imagine a world where P is true and Q false (no matter what exactly P says)? Again, type-A materialism can allow for that: even though P is true, it certainly isn't a priori. It could have turned out to be false. It could have turned out that the consciousness role is played by ectoplasmic property E. Then if "consciousness" is a rigid designator of whatever plays the consciousness role, a world where P is true but there's no E will be a world where P is true but Q false. So it is conceivable that things are such that there is a world where P is true and Q false.

(Compare the conceivability of a world where the watery stuff is H2O and yet there is no water: it is conceivable that water turns out to be XYZ, and in this case a counterfactual world where the watery stuff is H2O will be a world without water, just as, if water is H2O, a counterfactual world where the watery stuff is XYZ is a world without water. It is inconceivable, but conceivably possible that the watery stuff is H2O and yet there is no water.)

What the type-A materialist must reject, and what Dave Chalmers uses as premise in his zombie argument, is the conceivability of P and not-Q itself, not merely the conceivability of a world with P and not-Q, nor the conceivability of a world physically like ours but without consciousness.

So can we imagine that P is actually true while Q is false, in the way we can imagine that water is actually XYZ? To me at least, that's far from obvious. The "not-Q" bit alone is quite hard: could it turn out that nobody is, or ever was, conscious, including myself? Not sure. I guess there's no possible discovery or experience that could convince me of that.

Now Dave has an argument to back up his premise: P only gives us causal/structural information about the world, but any amount of that is a priori compatible with the absence of consciousness. In other words, the physical truths do not a priori entail the mental truths. In other words, type-A materialism is false. That's ok as far as it goes, but if one expected an argument against type-A materialism based on some facts about imaginability or conceivability, one obviously doesn't get one from here.


# on 05 December 2006, 16:20

This is a good point. I'd also note that the move from the possibility of zombies to the necessity (or even possibility) of dualism relies on the notion that if physicalism is false, we need something nonphysical to account for consciousness. But unless we construe the presumably nonphysical something-we-know-not-what as essentially conscious-making, zombies are every bit as "clearly and distinctly" conceivable (Chalmers' criterial phrase for metaphysical possibility) even on the dualist's picture.

Consider an arbitrary person, call him Al. On the assumptions of dualism, Al comprises or instantiates certain natural properties N and certain nonnatural properties O. The dualist postulates that N and O are necessary and sufficient conditions for consciousness. Yet we can "clearly and distinctly" conceive of zombie-Al, who is a duplicate of Al in respect of both N and O, but who is nonetheless phenomenally void.

This means that the zombie argument defeats dualism in just the same way it defeats physicalism. In fact, it would defeat any ontology that isn't stipulated a priori as containing ingredients essential to consciousness.

# on 06 December 2006, 11:19

yes, also a good point: merely adding ectoplasma doesn't seem to help at all. So the lesson from the anti-materialist arguments -- assuming they work -- can't merely be that there is more stuff in the world than just physical stuff. It must be something like: there are fundamental facts about the stuff in the world that can only be captured in phenomenal vocabulary.

# on 12 December 2006, 00:23

Hi Wo. Re your point in the last paragraph of the post, the argument that no amount of structural/dynamic truths a priori entail phenomenal truths is roughly that the only plausible route to such an entailment is a functional analysis of phenomenal concepts, and there's no such analysis. This isn't really intended as an argument against analytic functionalists, but as an argument against a priori-entailment materialists who aren't analytic functionalists. (In the taxonomy of "Consciousness and its Place in Nature", it's an argument against type-C materialists rather than type-A materialists.) The case against analytic functionalism turns on more basic intuitions: conceivability of functions without experience, knowledge gaps, explanatory gaps.

Re the penultimate paragraph: for me the conceivability of P&~Q is as strong as the conceivability of the possibility of P&~Q. Re the issue you mention, one can get around this by making Q be a truth about someone else's consciousness. Then e.g. I just need to conceive that things are physically like so (and that's all) and it's not the case that you are conscious. I think this is pretty straightforward -- e.g. it's the sort of thing we conceive all the time in the context of the problem of other minds. Claims about the conceivability of "nobody was ever conscious" aren't really required for the argument against materialism. (Though I do think it's conceivable that no-one was ever conscious. There's a big difference between "No experience could convince me of P" and "P is not conceivable".)

Re Q's point: It's not obvious that zombie argument works for arbitrary base properties O. Obviously it doesn't work when O includes fundamental phenomenal properties. It's also not out of the question that there are protophenomenal properties and concepts thereof such that there's an a priori relation between these concepts and phenomenal concepts. The zombie argument suggests that this won't work for a purely structural/dynamic base, but on the face of it these considerations don't generalize to an arbitrary base.

# on 22 January 2007, 03:06

David is right that the zombie argument wouldn't work with respect to "fundamental phenomenal properties," since (as I said) such properties are by stipulation essentially conscious-making. But since it's the zombie argument itself that lends color to the intuition that we need to appeal to fundamental phenomenal properties in the first place, I think this stipulation begs the question.

It's a simple enough exercise, e.g., to imagine a minimal physical duplicate of our universe that is "gravitationally void." But of course the implication of an ontologically separable domain of "fundamental gravitational properties" here strikes us as artificial because (1) we realize that gravity plays a *dynamic* role in the motion of bodies, and (2) we have the linking intuitive concepts to see at least roughly how that's so. Because it's so less clear to us how the structure of physical reality plays out *dynamically* in the generation of consciousness, however, the potentially illusory quality of an ontologically separable domain of fundamental phenomenal properties isn't as transparent.

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