Talk:Twin Earth thought experiment

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Assuming that both of these substances are called "water", wouldn't that depend on whether "water" refers to

A) A use that XYZ/H2O is put to. or B) What XYZ/H2O is made up of?

In other words, I believe whether or not "water" is the same on both Earths depends on context.

There is a closely related debate in the Philosophy of Language along these lines. There are those who believe that the meaning of a term such as 'water' is determined by descriptions of it - similar to your A above. Putnam, and those who value the Twin Earth thought experiments, however, believe that at least in many cases, a term such as 'water' refers indexically to that particular stuff (which we call 'water') whatever it in fact is. - Ncsaint 20:07, 13 October 2005 (UTC)

Contents 1 Twin Earth is exactly like Earth except for the absence of logic :-) 2 WTF 3 Putnam speaks of himself in third person? 4 Just goes to prove that philosophers are a waste of space 5 The Answer

[edit] Twin Earth is exactly like Earth except for the absence of logic :-)

I fail to understand how any philosopher can accept the notion of a Twin Earth that is exactly like Earth in all respects, except that water is not H2O. This is not even logically possible! For example: Do hydrogen and oxygen exist on Twin Earth? They must, otherwise it would hardly be true that Twin Earth is like Earth in all respects. But then, what happens when hydrogen and oxygen mix on Twin Earth? Do they form H2O? If so, then the original premise is invalid. If not, then they are somehow magically converted into XYZ. This means that either the laws of physics are completely different on Twin Earth (thereby invalidating the original premise), or XYZ is in fact the same chemical compound as H2O. The same holds true even if the argument uses something other than water. The basic assumption is: "Twin Earth is exactly like Earth except for X." But this assumption assumes that X is causally unrelated to everything else on the planet, which is clearly impossible. Therefore, it will never be possible to simply change one element of Earth and claim that nothing else changes. Hence, it seems to me that the entire argument falls apart. Not to mention: an even more ludicrous assertion is that my Twin Earth twin and I are "molecule-for-molecule identical." Perhaps Putnam did not realize that the human body is largely made of H2O :-).

Ron Karr

Hmm, perhaps 'XYZ' is functionally identical to 'H2O'? However, it is obviously not composed of 'H2O', therefore slightly changing the meaning of water on Twin-Earth? Meh, Davidson's Swampman argument attempts to demonstrate the same conclusion if you find the premises of Putnam's unsatisfactory.--Laplace's Demon 06:09, 19 June 2006 (UTC)

Do people actually use the utterance constantly rendered as 'meh' all over the Internet in real life, with real voices? Or is it just computerese? I have never heard anything equivalent to it.

Ron, I think that your first point, although valid chemistry, doesn't really hurt the thought experiment. But your second point -- the absurdity of claiming that Oscar and Twin-Oscar have identical brains, "molecule for molecule" (because most of the molecules in a brain are in fact water) seriously compromises the thought experiment. Perhaps this fact didn't occur to Putnam. I think his thought experiment makes more sense if the substances that Oscar and Twin-Oscar each call "water" is not a component of Oscar and Twin Oscar themselves.

Can anyone verify whether the "identical brains, molecule for molecule" is really in Putnam's writing? If not, I suggest we remove it. Lawrence King 06:07, 7 September 2006 (UTC)

I don't see the problem. The thought experiment specifies that this all happens before the beings of either planet have the ability to analyse H2O or XYZ. So the two sets of people use the same word to mean what (for them) is the exact same thing, The meaning of the word can't be "H2O" in one place and "XYZ" in the other because by definition, neither of them knows what this wet stuff is made of. The word's meaning is concise and identical in both places: "Clear wet stuff that we can drink". If we take all of the people from one earth and magically teleport them to the other (and vice versa) - nothing inconsistent happens - nobody is aware of any change whatever.

In fact, this situation has already happened right here on the real world. Water here on earth is made up of regular H2O and Deuterium hydroxide or 'heavy water' - aside from the fact that the deuterium atom weighs a bit more than regular hydrogen, they are chemically identical (deuterium is an isotope of hydrogen). If you are thirsty and you drink heavy water, you won't be thirsty anymore - it's clear and wet and forms droplets and you can float boats in it - it's water. Up until maybe the 1900's, we believed there was just one kind of water so (in effect) the word 'water' meant both kinds. Now we know differently and hence we have modified our terminology to reflect our new knowledge - so 'water' now means H2O and 'heavy water' describes the other kind. This is the exact same thing as these hypothetical people widely separated in space are doing - it doesn't matter that they are widely separated. There are two kinds of water (H20 and XYZ) that are functionally identical and one word suffices to describe both kinds. As soon someone from one world can compare samples of 'water' from both earths and do the chemical analysis, they'll discover that there are two chemically distinct types. Then they will modify their language so that they call one of them 'H2Owater' and the other 'XYZwater'. There is no ambiguity - nothing strange to report. We do this all the time...people saw elephants in Africa and elephants in India and just called them "elephants" - when we found that they were in fact distinct species - we called one "African Elephant" and the other "Indian Elephant"...nothing weird at all. SteveBaker 18:38, 7 September 2006 (UTC)

Water(our) and water(twin) is exactly the same material (or element if you like), there's no difference between them like water(our) is different from our heavy water. --Jambalaya 23:15, 7 September 2006 (UTC)

No - that's not what Putnam is saying. He says that H2O and XYZ are different compounds (which means there must be difference between them) - only that the beings do not yet posess the technology to differentiate them. This was also the case with water and heavy water in the real world, up until the point where we could separate them and we understood about the isotopes of hydrogen. Techinically, Deuterium is the same element as Hydrogen. They have the same number of electrons and protons - but Deuterium has an extra neutron. So H2O and D2O are made from the same elements. My analogy is correct...but use the one about elephants if it's clearer. SteveBaker 06:48, 8 September 2006 (UTC)

I was thinking more of water as an Aristotelian element, not as (chemical) compounds :-) --Jambalaya 16:44, 8 September 2006 (UTC)

[edit] WTF

Is this thought experiment supposed to be impressive? It seems to make no attempt at a true understanding of the world. -jjh

I concur somewhat, the thought experiment is entirely flawed because it is the incredibly peculiar property of water that causes it to expand when it freezes (i.e. grows when going from liquid to solid) that is greatly responsible for there being life on Earth. The thought experiment might be better improved if you just had a world where cats were called dogs and vice versa. There, in fact, we wouldn't really need a 'Twin Earth' we could just get two kids growing up, tell one that the pet is called a 'cat', tell the other 'dog', then argue about whether any of this helped anybody...ever? Better yet, we could improve this experiment by having the actual animal involved as a monkey... by which I mean a fish. ;) aj

[edit] Putnam speaks of himself in third person?

A line in the article says; "Putnam's original formulation of the experiment was this"

and then in the quote, second paragraph, this sentence occurs; "Yet, at least according to Putnam, when Oscar says water, the term refers to H2O..."

This leads me to believe that Putnam was speaking of himself in third person, something I doubt that he did. The wording "original formulation" makes me believe that this is actually Putnam's own words!

--Jambalaya 22:48, 7 September 2006 (UTC)

[edit] Just goes to prove that philosophers are a waste of space

Tell a child that water is in fact called "waber" and he will spend the rest of his life calling it "waber" - unless he is corrected. Tell a child that orange juice is called "water" and the same will happen - unless somes one tells him different, he will call it "water". In the twin world, no one questions the fact that this mystery liquid is called water because they've all been brought up being told that it's called "water"... it's a name for this liquid and nothing more! Seriously, Putnam needs to put his time to more beneficial use! What a waste of space.

Well, not all philosophers are a waste of space - and those that are tend only to waste space some of the time! For exmaple, the philosophical thought experiment of the Chinese room is quite valuable in thinking about artificial intelligence. SteveBaker 06:53, 8 September 2006 (UTC)

[edit] The Answer

This is a bit silly, but it has more to do with the conventions of language, than real philosophy. Whan I talk about 'My Mother' I am not talking about the same person as you are when you say 'My Mother'. These are two different people who serve the same role to each of us. Even if they look the same, act the same, etc. My mother is a different person than the person you refer to when you say 'My Mother'.

Yeah, but what are famous philosophers doing when they point things out that are so obvious. Has this observation about language made, or have the potential to make, any impact on the world. -jjh

Hi, it seems to me that some of you(Ron) are missing he point of the thought experiment. it is devised as a way of teasing out the nature of logic and our language. the point you are missing is that this is all conceptual, no one is making a claim that it could ever happen, merely that it is concieveable. If you really want to criticize a thought experiment please use a logical schema rather than being so pedantic about little details.