Talk:Twin Earth thought experiment

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)

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)

Neither of your analogies are functional. First, D2O will kill you if you drink it to the exclusion of H2O. This means that D2O does not have identical functionality and properties to H2O. In fact, there really isn't ANY compound that has identical properties to water - the fundamental theory of chemistry, which has been proven time and time again over the past 200 years is that structure determines function, and a change in structure changes function. The problem with the thought experiment is that it results in no useful conclusions because its premise isn't even remotely plausible. As for the elephants, they're irrelevant to the fundamental flaws in the thought experiment, as elephants are not necessary for human life, nor human thought, unlike water. StellarFury (talk) 20:59, 5 October 2008 (UTC)

William Poundstone's book Labyrinths of Reason contains some discussion of the chemistry aspect of Twin Earth-- what chemical could possibly fill in for water without being water? He comes up with some possible answers(ammonia, hydrogen sulfide(H2S), the liquid forms of gases) but concludes that they'd just make Twin Earth too different to be remotely Earthlike. I find this still works if you accept that water is chemically the same everywhere, but the philosophical issues derive from Oscar and Twin!Oscar thinking about different but parallel bodies of water-- can they be having different thoughts if they're both thinking of the "Atlantic Ocean" and their brains may be identical? (Poundstone also suggests a variant with something less vital than water, like the roles and names of more obscure elements being swapped.) In that case Oscar and his Twin's thoughts might be superficially different but similar under examination. 69.224.182.55 (talk) 19:07, 17 May 2008 (UTC)

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

I mostly agree with the two above comments (see my previous post in the section directly below) but I think (I have a math/physics background, not philosophy) this "thought experiment" is getting at (badly IMHO) is the distinction between what we use a word to describe (given our inherently subjective, limited and fuzzy knowledge of the named entity) and what it physically is (assuming you subscribe to Realism of course!). Annoyamouse (talk) 04:46, 10 November 2011 (UTC)

Flawed: Contradicts or diverges from the known state of affairs?

In the thought experiment it says twin-water (XYZ) is chemically NOT water (H2O) - i.e. they are different molecules. It then contradicts this in the statement "their brains are molecule-for-molecule identical". Brains are mostly made of water (H2O), so twin-brains would be mostly twin-water (XYZ). Thus, their brains are NOT molecule-for-molecule identical! It is also a scientific fact that different chemical molecules tend to behave in significantly different ways, and specifically water (H2O) has very special and specific properties (especially in regards to biology) not shared by any other compounds, rendering such a thought experiment impossible. A planet with XYZ instead of H2O is very unlikely to evolve life as we know it, and would be in no way isomorphic to our own world. The thought experiment ignores the complexities of physical reality and the myriad changes that would result (think the butterfly effect in chaos theory) from replacing H2O with a different molecule. This is a well known danger in thought experiments when they diverge to far from the known state of affairs. Annoyamouse (talk) 04:31, 10 November 2011 (UTC)

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)

It isn't a quotation at all, although the layout and the square brackets make it look like one. The quotation is rather long, however, so I just remove the box. Rathgemz (talk) 22:30, 17 November 2014 (UTC)

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)

I'll second SteveBaker here. I tend to read philosophy (especially ancient Greek) with a pinch of salt and view it generally as much less rigorous than math and the (hard) sciences; mind you, I have a math/physics background and so I could be bias. However, I think math, science and many subjects are severely weakened when devoid of philosophical debate. I really don't like the "shut up and calculate" school of thought. IMHO the interpretation and meaning of quantum mechanics is a good example of this type of debate, as is meta-mathematics like Godel's incompleteness theorem. I also agree with SteveBaker's comment on the Chinese room thought experiment and would add the related "Chinese nation" thought experiment too. IMHO philosophy without science is unfalsifiable, and science without philosophy is unimaginative; together they are more than their sum. Just my two cents. :-) Annoyamouse (talk) 05:09, 10 November 2011 (UTC)

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.

Well, duh.

Of course none of us actually, when we use the word water, have associated in our minds ALL of the properties of the substance we know as water with the word, or the image the word invokes. Just as people once didn't have in their mental images of the word water the idea that it was composed of oxygen and hydrogen, we don't even now know water from every single possible viewpoint. There are still properties of water we have never experienced. There are still properties of all things in our physical universe that we haven't, and for some of those properties, will never, experience or know about. We have only been experiencing some small portion of the real world all our lives. As far as the twin earth argument, I don't believe it is possible to have two worlds with the only difference being the chemical composition of what is called water. The universe is a nonlinear sort of place, so that any difference in initial condition, no matter how small, would result in vast differences between the state of the two worlds. Perhaps the people on this twin earth would not even eat ice cream, since, if made with XYZ, it would taste thoroughly unappealing. There would have to be some difference beyond the replacement of H2O with XYZ, as this would automatically produce differences elsewhere. Putnam demonstrates not only his inability to reason through an argument to a profitable conclusion, but also his complete lack of knowledge of what an informed person now knows about water, chemistry, and physics. It is even worse than his argument against brains in a vat being able to think about being brains in a vat, and just as useless. —Preceding unsigned comment added by 74.226.64.128 (talk) 21:37, 27 November 2007 (UTC)

Some remarks about Dennett

Consider that in Dennett's terms, intuition pump isn't pejorative at all, like it is suggested here. There can be good and bad thought experiments of course, but in general intuition pumps are very useful. Dennett himself is the inventor of numerous intuition pumps.

Not to mention that putting Dennett's allegedly negative attitude about intuition pumps as the argument against Twin Earth experiment seems to be entirely missed, because Dennett shares the intuition of Putnam's externalism regarding to mental content. His detailed view can be found in "Evolution, Error and Intentionality".

83.168.75.17 (talk) 11:35, 23 February 2008 (UTC)AW

Which criticism? Source?

This is the article right now: "Putnam, who is well known for changing his philosophical positions on a variety of issues, criticizes the experiment later in life because it is anti-functionalist." - in which way did he criticize it? Is there any source on this? Just saying that he critisized it gives very little important information. Ran4 (talk) 04:20, 24 April 2009 (UTC)

Conclusion

A few remarks:

• The article lacks a conclusion that can be inferred or the conclusion that the author drew from the experiment, possibly one of the most important things. I, as someone who had never heard of this prior to reading this article, still don't know what the author was trying to prove with this mental experiment.

• Also, the section of objections is disproportionately larger than the rest of the article. Pikolas (talk) 05:37, 16 October 2011 (UTC)

Forget twinwater, just have twinParis :)

By using a geographical location instead of modifying water, you wouldn't have to deal with breaking chemistry, you don't have to change anything actually. When one of them says Paris, certainly they're talking about their own Paris and not the twin's, yet in their heads it's exactly the same even though the two Paris are many light years apart. --TiagoTiago (talk) 14:27, 25 October 2011 (UTC)

I completely agree with you that "Twin Earth" is a very poorly conceived thought experiment (see my previous posts) and from what your "twinParis" idea, I think your talking about label isomorphism, but IMHO a potential problem with your suggestion is that it loses [what I, at least, see as] a key question posed by the thought experiment: What does a label (such as a word or term) truly describe when there's significant ignorance about the nature of the entity the label's attached to? In the case of water/twin-water it's posing the question of whether the label "water" should be interpreted as referring to the subjective collection of "perceived properties and attributes" by the human mind [e.g. a fairly colorless and tasteless liquid] verses the objective collection of "actual properties and attributes" of the molecular constituents (H₂0 for water, XYZ for "twin-water").

IMHO, this is really a basic question about whether one interprets linguistic labels as subjective, transjective [in-between subjective and objective] or objective: Are labels mental constructs employed by us to describe (a) our subjective personal experience of Reality, (b) our transjective scientific understanding of Reality, or (c) the objective inherent nature of Reality? A potential solution to this problem is to distinguish between the three, having a label to describe each: e.g., "subjective water", "transjective water" and "objective water". It's worth noting thought that although neither the subjective or objective changes significantly over time ["subjective water" is always wet, and "objective water" is always whatever H₂0 sub-atomically reduces to] the tranjective [our "scientific understanding of water"] generally moves from the subjective towards an objective description, with scientific progress.

Water is a perfect example of this: When asked "What is water?", a caveman's best description would be highly subjective (e.g. "wet stuff I drink"), whereas even a high school kid can reply "H₂0", which is a considerably more objective description of water. Annoy@mouse ⁾ 13:32, 15 December 2011 (UTC)

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Molecule-for-molecule identical?

Oscar and Twin Oscar's brains couldn't possibly be molecule-for-molecule identical, as Oscar's brain is comprised partially of H₂O and Twin Oscar's of XYZ. The two papers referenced only claim that their psychological states are identical. Cocaineninja (talk) 15:59, 9 August 2019 (UTC)

Image suggestion

Shouldn't the two earths in the picture look the same? It would fit the thought experiment better