Why won't you die like a nice undead?

On The Stone, Gary Gutting takes on the admirable task of defending the Knowledge Argument and the Zombie Argument. I find it rather puzzling that Gutting puts the Zombie Argument specifically in terms of logical, rather than metaphysical, possibility. For example, he writes:

The basic premise of the Zombie Argument is that my zombie-twin is logically possible (and therefore that laws of nature connecting physical make-up with experiences are not logically necessary, even if they are physically necessary). [original emphasis]

From the logical possibility of a zombie-twin, Gutting claims, it follows that

my experiences involve something beyond my physical makeup. For my zombie-twin shares my entire physical makeup, but does not share my experiences. This, however, means that physical science cannot express all the facts about my experiences.

But does it really follow? How does it follow from "it is logically possible that I have a zombie-twin with the same physical makeup as mine" that "my own experiences are not entirely physical"? After all, the first claim is about what is logically possible (i.e., the idea of a zombie-twin is not logically contradictory), whereas the second claim is about what is actual (i.e., the actual phenomenon of consciousness).

To see the problem, consider the following:

1. It is logically possible that terrestrial organisms are silicon-based.
2. Therefore, terrestrial organisms are not entirely carbon-based.

Does (2) follow from (1)? I think not. So what can logical possibilities tell us about what is actual? Is there something like a "could-is gap"? (That is, in more or less the same way that from "p is the case" it doesn't follow that "p ought to be the case," from "p could be the case" it doesn't follow that "p is the case.")

[cross-posted at my blog]

Comments

[Alex]

If I remember correctly, the zombie arg. is supposed to show that phenomenal properties don't (strongly) supervene upon physical properties (and a fortiori aren't identical to them). A zombie instantiates all the physical properties you do, but has none of your phenomenal properties. So if a zombie is logically possible *and* the right set of PWs over which to formulate the supervenience claim at hand is the set of logically possible worlds, then phenomenal properties don't (strongly) supervene upon physical ones (but then I'm pretty sure Chalmers talks about metaphysical, not logical, possibility in his arg.).

So, there's more to your instantiating the phenomenal properties you *actually* instantiate than simply your instantiating whatever physical properties you *actually* instantiate (there has to be, since instantiating the latter doesn't necessitate - logically or metaphysically - instantiating the former).

[Moti Mizrahi]

Thanks for the comment, Alex.

I think you’re right that Chalmers’ version of the zombie argument is cached out in terms of metaphysical possibility. But I’m not interested in the zombie argument per se, but rather in the inference from logical possibilities to actualities. Gutting claims that “given ‘Zombies are [logically] possible’ the inference to ‘My experience is non-physical’ is very quick and easy.” Rather than being quick and easy, this inference looks like a non-sequitur to me.

Gutting himself says that p is logically possible just in case p is not logically contradictory. So, according to Gutting, from ‘p is not logically contradictory’ it is supposed to follow that ‘p is the case’. Is this a valid inference? Consider this analogous inference:

1. The idea of silicon-based terrestrial life is not logically contradictory.
2. Therefore, terrestrial life is silicon-based.

This looks like a non-sequitur to me. Similarly:

1. The idea of a being whose conscious experience does not supervene on its physical makeup is not logically contradictory.
2. Therefore, I am a being whose conscious experience does not supervene on its physical makeup.

also looks like a non-sequitur. Even if the idea of a zombie-twin is not logically contradictory, I don’t think that, by itself, it implies anything about actual human beings.

[Dan Dennis]

As I understand it, if the mental supervenes upon the physical this means that any changes to the mental are correlated with changes in the physical, but there can be changes in the physical without any corresponding changes in the mental. However, even if the mental does supervene upon the physical, this does not mean that the mental ‘is’ physical. It means that there is something non-physical – the mental – which changes when the physical changes in certain ways.

I think Gutting is saying that the possibility of zombies means that in some possible worlds there are beings for whom those physical changes are not accompanied by any changes in the mental. If the mental was identical to the physical (in the way that the morning star is identical to the evening star) then you could not have one without the other, so there could be no zombies.

If I understand him correctly Gutting is also saying it may or may not be that in our world there are rigid (what Davidson calls) psychophysical laws ensuring that certain changes in the physical world (e.g. in the brain) are accompanied by certain changes in the mental (ie certain experience). We do not currently know, and we do not know whether it is possible to find out.

[Moti Mizrahi]

Hi Dan,

The quotes in the post suggest that Gutting thinks that the mere *logical* possibility of zombies allows one to infer that conscious experience is non-physical. That is, he seems to think that the following is a valid inference:

1. That the mental does not supervene on the physical is not logically contradictory.
2. Therefore, the mental does not supervene on the physical.

The move from logical possibilities to actual facts looks like a non-sequitur to me.

Even if we introduce metaphysical possibility instead of logical possibility, the following still looks invalid:

1. There are possible worlds in which there are beings for whom the mental does not supervene on the physical.
2. Therefore, in the *actual world*, the mental does not supervene on the physical.

The move from possible worlds to the actual world looks like a non-sequitur to me (at least without a huge metaphysical baggage). After all, consciousness is a real phenomenon in the actual world and physicalism is a thesis about the actual world.

[Dan Dennis]

Hi Moti

Is Gutting’s thought the following? If consciousness is identical to the physical then zombies would be inconceivable.

Consider the following analogy. It is inconceivable that the morning star is not the evening star because they are both the same planet, Venus. In every possible world, Venus is Venus.

Thus, if there are possible worlds where there are zombies then the physical is not identical to the mental. Because if the physical is identical to the mental then you cannot have the physical without the mental. Thus if you think that there are possible worlds containing zombines then you think that the physical is not identical to the mental, full stop.

However, even if the physical is not identical to the mental (in this or any world) nevertheless in this world the mental may supervene on the physical.

It remains open to the physicalist to deny that there are any possible worlds containing zombies, and thereby to allow that the physical is identical to the mental.

[Dan Dennis]

Ps Perhaps I should add, to someone who is sufficiently well informed, ‘It is inconceivable that the morning star is not the evening star.’ Once you are sufficiently well informed, to deny that the evening star is the morning star is to deny that venus is venus.

However, to someone who is not sufficiently well informed, it is conceivable that the morning star is the evening star. So the phsyicalist would argue that once one is sufficiently well informed, then one will realise that the physical is identical to the mental, and so zombies will be inconceivable. It is only our current ignorance which allows us to conceive of zombies. Thus, that we can conceive of zombies is neither here nor there, he will claim…

[Moti Mizrahi]

Thanks for the follow-up, Dan.

I think you are right about the Venus case. But the physicalist could argue that the Venus case and the mental case are not quite analogous. As you said in your previous comment, to say that the mental supervenes on the physical is not to say that the mental is the physical. Rather, it is to say that there is no mental change without a corresponding physical change. In that case, unlike the morning star and the evening star, which are one and the same, the mental and the physical are NOT one and the same, in which case, it is conceivable that the former does not supervene on the latter. So zombies are conceivable even if physicalism is true. All that follows from that, however, is that there are some possible worlds in which the mental does not supervene on the physical. It does not follow that the actual world is one of those possible worlds.

[Dan Dennis]

Well it depends how you define physicalism. The stanford encyclopedia http://plato.stanford.edu/entries/physicalism/
opens with 'Physicalism is the thesis that everything is physical, or as contemporary philosophers sometimes put it, that everything supervenes on, or is necessitated by, the physical.' This is ambiguous. If physicalism is the thesis that everything - including the mental - IS physical then the conceivability of zombies implies that physicalism is false (as explained in my earlier posts). If physicalism is defined as supervenience of the mental on the physical, and if it is allowed that the mental and the physical may be different things despite this supervenience of the one on the other then physicalism *may* be true even if zombies are conceivable.

[Moti Mizrahi]

“If physicalism is the thesis that everything - including the mental - IS physical then the conceivability of zombies implies that physicalism is false (as explained in my earlier posts).”

Well, as you said in an earlier comment, physicalists could argue that dualists are (mis)conceiving of zombies just as people who are ignorant of philosophical astronomy are (mis)conceiving of the morning star as being distinct from the evening star.

I think what this shows is that, contrary to what Gutting claims, there are no "quick and easy" inferences from possibilities (logical or metaphysical) to actualities.