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Wednesday, April 28, 2010

Defending the Incompatibility Argument

In my last post, I argued that the knowledge argument and the conceivability argument are incompatible, which is interesting if only because they are commonly supported together in attacks against physicalism. Torin Alter has just emailed me saying that Mary Z has appeared in the literature already, and even in an argument similar to--though perhaps not identical with--my own (see McGeer, 2003). I haven't read his references, so I cannot comment on any of that yet. What I want to do here is defend my incompatibility argument against possible objections, including one raised in Torin Alter's email.

First, a brief review of the incompatibility argument:

  1. If zombies are conceivable, then we can conceive of Mary Z, a zombie version of the original Mary (hereafter 'Mary O').
  2. If zombies are conceivable, then Mary Z gains knowledge when she leaves her black-and-white room.
  3. If zombies are conceivable, then Mary Z's new knowledge does not entail non-physical facts.
  4. If zombies are conceivable, then Mary O gains whatever knowledge Mary Z gains.
  5. Therefore, if zombies are conceivable, then Mary O gains new knowledge which does not entail non-physical facts.
  6. If the knowledge argument is sound, then Mary O's new knowledge entails non-physical facts.
  7. Therefore, if zombies are conceivable, the knowledge argument is not sound.
  8. Therefore, the conceivability argument and the knowledge argument are incompatible.
Supporters of both the conceivability and zombie arguments might respond by claiming that Mary Z does not learn what Mary O learns: Mary O learns what it is like to see colors, but Mary Z cannot learn what it is like to see colors. However, this response is not to the point, because the incompatibility argument says nothing about whether or not Mary O learns anything over above what Mary Z would learn, if she were conceivable. The incompatibility argument is more subtle than that.

The incompatibility argument shows that, if zombies are conceivable, then Mary O gains new knowledge which does not entail non-physical facts. This is true regardless of whether or not Mary O also happens to gain knowledge which does entail non-physical facts. Therefore, the fact that Mary O gains new knowledge is insufficient to draw the conclusion that she gains knowledge which entails non-physical facts. If we want to claim that Mary O gains knowledge of non-physical facts--or knowledge which entails non-physical facts--then we must claim more than what is stipulated by the knowledge argument. Specifically, we must stipulate that phenomenal knowledge entails non-physical facts; but that is precisely what the knowledge argument was supposed to demonstrate. We cannot reformulate the knowledge argument with that stipulation without begging the question against physicalism.

Torin Alter objects: "I don't see why we should agree that zombie Mary learns anything. Of course, she may say that she has learned something, but why should we believe her?"

Of course, zombie enthusiasts will not grant that Mary Z learns what it is like to see colors. However, I think they must accept that she learns something upon her release from her black-and-white room. To see why, imagine the following experiment.

Before Mary Z leaves her black-and-white room, we show her some colors. She says they look unlike anything she has ever seen before. As Alter notes, we need not believe her. However, thanks to a machine scanning her neural activity, we see that her brain is in states it has never been in before. Something new is going on in her brain which correlates with her reports of new experiences, as the zombie argument requires--for Mary Z must be a physical and functional duplicate of Mary O. So Mary Z need not be experiencing what it is like to see colors (whatever that is), but something new is going on in her brain. Does this "something new" constitute new knowledge? Maybe not. Let's continue.

Now we teach Mary Z the names of some of these colors, and we test her memory of the names of the colors. Again, during this activity, our neural scan shows unprecedented activity. She seems to be able to do something she couldn't do before. In fact, her neurological activity is exactly like Mary O's when we performed the same experiment on her. So it would seem that, even if Mary O experiences something Mary Z has not experienced, they have both acquired new abilities which are in some respect the same. Does this new shared ability constitute new knowledge? I think it does. Mary Z learns to use names to correctly identify colors.

Some might argue that my proposed experiment would not work the way I claim. They might say that Mary Z could not learn how to use names to identify colors. Yet, if this is true, the conceivability argument fails; for zombies are supposed to function exactly like human beings. If human beings can identify colors with names, then so can zombies. The only difference, supposedly, is that normal human beings can do more--we can also access non-physical properties of color vision.

Indeed, if we suppose that zombies cannot learn to identify colors, then how could they learn to identify any objects? How could they identify tables or chairs? How could they identify sounds or textures? A zombie who could not learn how to identify objects and properties would not be able to learn anything at all, and would not function like a human being. Thus, for the conceivability argument to work, zombies must be able to learn how to use names to identify colors. And clearly Mary Z cannot do this from inside her black-and-white room. She must wait until she has access to colors (even if she lacks access to their phenomenal properties, if such properties be non-physical).

I can see only one way to make Alter's objection work, and it is not attractive. It requires regarding knowledge as absolutely unobservable, as absolutely disconnected from observable behavior. If we are to deny that Mary Z gains knowledge, then knowing cannot be demonstrated in any way, by any set of abilities or capacities. Thus, for Alter's objection to work, we must supplement both the zombie and knowledge arguments with an implausible view of knowledge--a view which holds that knowledge is not demonstrated with the correct use of language, or the learned following of rules. If this view is adopted, we must eternally wonder how anyone could ever know that anyone ever knew anything.


McGeer, Victoria (2003) "The Trouble With Mary" Pacific Philosophical Quarterly, 84, 4, pp. 384-393.