Be careful with thought experiments

lukeprog

9 Be careful with thought experiments

18th May 2012

2 min read

9

Thagard (2012) contains a nicely compact passage on thought experiments:

Grisdale’s (2010) discussion of modern conceptions of water refutes a highly influential thought experiment that the meaning of water is largely a matter of reference to the world rather than mental representation. Putnam (1975) invited people to consider a planet, Twin Earth, that is a near duplicate of our own. The only difference is that on Twin Earth water is a more complicated substance XYZ rather than H2O. Water on Twin Earth is imagined to be indistinguishable from H2O, so people have the same mental representation of it. Nevertheless, according to Putnam, the meaning of the concept water on Twin Earth is different because it refers to XYZ rather than H2O. Putnam’s famous conclusion is that “meaning just ain’t in the head.”

The apparent conceivability of Twin Earth as identical to Earth except for the different constitution of water depends on ignorance of chemistry. As Grisdale (2010) documents, even a slight change in the chemical constitution of water produces dramatic changes in its effects. If normal hydrogen is replaced by different isotopes, deuterium or tritium, the water molecule markedly changes its chemical properties. Life would be impossible if H2O were replaced by heavy water, D2O or T2O; and compounds made of elements different from hydrogen and oxygen would be even more different in their properties. Hence Putnam’s thought experiment is scientifically incoherent: If water were not H2O, Twin Earth would not be at all like Earth. [See also Universal Fire. --Luke]

This incoherence should serve as a warning to philosophers who try to base theories on thought experiments, a practice I have criticized in relation to concepts of mind (Thagard, 2010a, ch. 2). Some philosophers have thought that the nonmaterial nature of consciousness is shown by their ability to imagine beings (zombies) who are physically just like people but who lack consciousness. It is entirely likely, however, that once the brain mechanisms that produce consciousness are better understood, it will become clear that zombies are as fanciful as Putnam’s XYZ. Just as imagining that water is XYZ is a sign only of ignorance of chemistry, imagining that consciousness is nonbiological may well turn out to reveal ignorance rather than some profound conceptual truth about the nature of mind. Of course, the hypothesis that consciousness is a brain process is not part of most people’s everyday concept of consciousness, but psychological concepts can progress just like ones in physics and chemistry. [See also the Zombies Sequence. --Luke]

Personal Blog

9

New Comment

Rendering 0/98 comments, sorted by

top scoring

(show more) Click to highlight new comments since: Today at 5:50 AM

Some comments are truncated due to high volume. (⌘F to expand all)Change truncation settings

Moderation Log

9 Be careful with thought experiments

by lukeprog

18th May 2012

2 min read

9

Thagard (2012) contains a nicely compact passage on thought experiments:

Grisdale’s (2010) discussion of modern conceptions of water refutes a highly influential thought experiment that the meaning of water is largely a matter of reference to the world rather than mental representation. Putnam (1975) invited people to consider a planet, Twin Earth, that is a near duplicate of our own. The only difference is that on Twin Earth water is a more complicated substance XYZ rather than H2O. Water on Twin Earth is imagined to be indistinguishable from H2O, so people have the same mental representation of it. Nevertheless, according to Putnam, the meaning of the concept water on Twin Earth is different because it refers to XYZ rather than H2O. Putnam’s famous conclusion is that “meaning just ain’t in the head.”

The apparent conceivability of Twin Earth as identical to Earth except for the different constitution of water depends on ignorance of chemistry. As Grisdale (2010) documents, even a slight change in the chemical constitution of water produces dramatic changes in its effects. If normal hydrogen is replaced by different isotopes, deuterium or tritium, the water molecule markedly changes its chemical properties. Life would be impossible if H2O were replaced by heavy water, D2O or T2O; and compounds made of elements different from hydrogen and oxygen would be even more different in their properties. Hence Putnam’s thought experiment is scientifically incoherent: If water were not H2O, Twin Earth would not be at all like Earth. [See also Universal Fire. --Luke]

This incoherence should serve as a warning to philosophers who try to base theories on thought experiments, a practice I have criticized in relation to concepts of mind (Thagard, 2010a, ch. 2). Some philosophers have thought that the nonmaterial nature of consciousness is shown by their ability to imagine beings (zombies) who are physically just like people but who lack consciousness. It is entirely likely, however, that once the brain mechanisms that produce consciousness are better understood, it will become clear that zombies are as fanciful as Putnam’s XYZ. Just as imagining that water is XYZ is a sign only of ignorance of chemistry, imagining that consciousness is nonbiological may well turn out to reveal ignorance rather than some profound conceptual truth about the nature of mind. Of course, the hypothesis that consciousness is a brain process is not part of most people’s everyday concept of consciousness, but psychological concepts can progress just like ones in physics and chemistry. [See also the Zombies Sequence. --Luke]

Personal Blog

9

New Comment

Rendering 0/98 comments, sorted by

top scoring

(show more) Click to highlight new comments since: Today at 5:50 AM

Some comments are truncated due to high volume. (⌘F to expand all)Change truncation settings

Moderation Log

More from lukeprog

Curated and popular this week

98Comments

Comment Permalink

komponisto14y160

I've always thought this argument of Putnam's was dead wrong. It is about the most blatant and explicit instance of the Mind Projection Fallacy I know.

The real problem for Putnam is not his theory of chemistry; it is his theory of language. Like so many before and after him, Putnam thinks of meaning as being a kind of correspondence between words and either things or concepts; and in this paper he tries to show that the correspondence is to things rather than concepts. The error is in the assumption that words (and languages) have a sufficiently abstract existence to participate in such correspondences in the first place. (We can of course draw any correspondence we like, but it need not represent any objective fact about the territory.)

This is insufficiently reductionist. Language is nothing more than the human superpower of vibratory telepathy. If you say the word "chair", this physical action of yours causes a certain pattern of neurons to be stimulated in my brain, which bears a similarity relationship to a pattern of neurons in your brain. For philosophical purposes, there is no fact of the matter about whether the pattern of neurons being stimulated in my brain is "correct" or not; there are only greater and lesser degrees of similarity between the stimulation patterns occurring in my brain when I hear the word and those occurring in yours when you say it.

The point that Putnam was trying to make, I think, was this: our mental concepts are causally related to things in the real world. (He may also, ironically, have been trying to warn against the Mind Projection Fallacy.) Unfortunately, like so many 20th-century analytic philosophers, he confused matters by introducing language into the picture; evidently due to a mistaken Whorfian belief that language is so fundamental to human thought that any discussion of human concepts must be a discussion about language.

(Incidentally, one of the things that most impressed me about Eliezer's Sequences was that he seemed to have something close to the correct theory of language, which is exceedingly rare.)

The real danger of thought experiments, including this one of Putnam's, is that fundamental assumptions may be wrong.

bryjnar14y20

That's an interesting solution to the problem of translation (how do I know if I've got the meanings of the words right?) you've got there: just measure what's going on in the respective participants' brains! ;)

There are two reasons why you might not want to work at this level. Firstly, thinking about translation again, if I were translating the language of an alien species, their brain-equivalent would probably be sufficiently different that looking for neurological similarities would be hopeless. Secondly, it's just easier to work at a higher level of ab... (read more)

7Tyrrell_McAllister14y

I'm not sure how you can appeal to map-territory talk if you do not allow language to refer to things. All the maps that we can share with one another are made of language. You apparently don't believe that the word "Chicago" on a literal map refers to the physical city with that name. How then do you understand the map-territory metaphor to work? And, without the conventional "referentialist" understanding of language (including literal and metaphorical maps and territories), how do you even state the problem of the Mind-Projection Fallacy? [...] It is hard for me to make sense of this paragraph when I gather that its writer doesn't believe that he is referring to any actual neurons when he tells this story about what "neurons" are doing. [...] Suppose that you attempt an arithmetic computation in your head, and you do not communicate this fact with anyone else. Is it at all meaningful to ask whether your arithmetic computation was correct? [...] Eliezer cites Putnam's XYZ argument approvingly in Heat vs. Motion. A quote: [...] See also Reductive Reference: [...] ETA: The Heat vs. Motion post has a pretty explicit statement of Putnam's thesis in Eliezer's own words: [...] (Bolding added.) Wouldn't this be an example of "think[ing] of meaning as being a kind of correspondence between words and either things or concepts"?

7Wei Dai14y

You've probably thought more about this topic than I have, but it seems to me that words can at least be approximated as abstract referential entities, instead of just seen as a means of causing neuron stimulation in others. Using Putnam's proposed theory of meaning, I can build a robot that would bring me a biological-cat when I say "please bring me a cat", and bring the twin-Earth me a robot-cat when he says "please bring me a cat", without having to make the robot simulate a human's neural response to the acoustic vibration "cat". That seems enough to put Putnam outside the category of "dead wrong", as opposed to, perhaps, "claiming too much"?

See in context