Tuesday, September 18, 2012

[PHI 3000] One's modus ponens is another's modus tollens

Hilary Putnam introduced the notion of "multiple realizability" and used it to argue against mind-brain identity theories as follows:
  1. If creatures with physical makeups that are different from ours (e.g., silicon-based androids and martians made of green slime) can realize the same mental kinds that we can realize (e.g., pain), then no mental kind is identical to any specific physical kind (e.g., C-fiber firing).
  2. Creatures with physical makeups that are different from ours can realize the same mental kinds that we can realize.
  3. (Therefore) No mental kind is identical to any specific physical kind.
In response, identity theorists could argue as follows:
  1. No mental kind is identical to any specific physical kind only if creatures with physical makeups that are different from ours can realize the same mental kinds that we can realize.
  2. Creatures with physical makeups that are different from ours cannot realize the same mental kinds that we can realize.
  3. (Therefore) It is not the case that no mental kind is identical to any specific physical kind.
Both arguments are valid. Which do you find more convincing?

6 comments:

  1. Explain how the second argument doesn't beg the question?

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    1. I assume that by "begs the question," you don't mean that the second argument is circular, but that it assumes as a premise a claim that a dualist doesn't accept (specifically, premise 2). If that's what you mean, then the second argument begs the question just as the first one does. For the first argument also assumes as a premise a claim that a physicalist doesn't accept (specifically, premise 2). After all, for a physicalist, there is only one kind of stuff—physical stuff. So, from a physicalist point of view, what could it mean to say that creatures have physical make-ups that are different in kind? I suppose that is what Putnam had in mind when he said that "one philosopher's modus ponens is another philosopher's modus tollens."

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  2. Hi Moti. There are many physicalists who could accept premise 2. Non-Reductive Token Materialists, who embrace both the multiple realizability and context dependence of higher level properties with respect to lower level properties, can hold that while two objects may differ in the arrangement of their atoms, they might have the same higher level property (like being the same size or weight, or being the same belief), and that objects with the very same physical structure might have different higher level properties (like being the very same sequence in computer memory, but representing different variables depending on what program was running at the time, or being the very same valve structure, but being either a choke or a throttle depending on where in the engine the valve is placed). If you're interested, you might check out Tyler Burge, for example.

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    1. Hi Pete, thanks for your comment.

      I am not sure it is correct to say that A and B are “different in kind” if A has one atomic structure and B has another. After all, both A and B are made of the same kind of stuff, i.e., physical stuff. Also note that this is a mere conceivability claim, i.e., A and B could have the same higher level properties but different arrangement of atoms. I am not sure why a physicalist (of one stripe or another) needs to worry about this. After all, physicalism is a thesis about the actual world; it says that the actual world is made of physical stuff. From the claim that A and B could have the same higher level properties but different arrangements of atoms it doesn’t follow that A and B actually have such properties and such arrangements.

      Be that as it may, your comment also shows that the MR thesis doesn’t entail in any straightforward way that physicalism (of one sort or another) is false. Since, if p (e.g., physicalism) and q (e.g., the MR thesis) are logically consistent (given that some can consistently hold both), then it is not the case that q entails not-p.

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  3. Hi Moti, thanks for the reply! I take your point about kinds - it depends on what you and I want to count as real kinds. However, the phenomenon of MR, once you start looking for it, is present with respect to a wide variety of kinds used in various sciences. Take, for example, biological kinds, like "heart." This kind term is used in causal explanations in biology, but there are many different instantiations of "being a heart" present in the animal kingdom. If MR is widely present with respect to scientific kinds, then it shouldn't be surprising or weird or spooky to find out that MR applies to the relationship between mental kinds and brain kinds, too. Of course, this last claim is exactly what you're pressing on above, as I see it, so I don't mean to simply assert it here. At least, though, if MR is as common as I claim, this would mean that mental properties wouldn't need to be special in order to be MR with respect to brain properties.

    I think you're right that MR doesn't entail that physicalism is false. In your original post, the conclusion by Putnam is that type-type identity of mental kinds and physical kinds (a relationship like "water=H2O" or "heat=mean molecular kinetic energy") fails. I don't agree with Putnam that MR by itself entails the failure of type-type identity, though I do think it presents a challenge to physicalists who endorse this view. Some, like Jaegwon Kim, respond by saying that higher-level properties are identical to complex sets of lower-level properties that make up all of the possible instantiations of the higher-level property. For one who endorses token identity (every token of a higher-level kind - each heart - is a physical thing, but higher-level properties do not reduce to lower-level properties), if the view holds up, Putnam's argument isn't a challenge at all.

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    1. Thanks for the reply, Pete.

      Glad we agree that MR doesn’t entail that physicalism is false.

      I also agree with you that the way to make MR more than a mere conceivability claim is by appeal to some sort of analogical argument.

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