Question This is a question about Hilary Putnam's twin earth thought experiment. After I read this thought experiment I was not convinced that Oscar's and twin-Oscar's "water" concept have different meanings. But most of the philosophers' intuitions are similar to Putnam (i.e., they think that Oscar's and twin-Oscar's "water" concept have different meanings). I thought that there might be something wrong with me. So I told this thought experiment to different people with different origins but without exception all of them responded that both Oscar's and twin-Oscar's "water" concept have the same meaning. So I still do not understand, why do so many philosophers' intuitions work like Putnam's? Thank you, Deniz

Accepted:
October 5, 2005

Comments

'Water' is a natural-kind term, and the natural-kind that 'water' refers to turned out to be H2O. In every possible situation, 'water' refers only to quantities of H2O. Twin-water is of a different natural kind, say, XYZ. The idea is that physical natural-kinds are defined by what they are made up of. So, the stuff made up of XYZ (and not H2O) is not water.

The intuition that the XYZ-stuff on twin earth really is water may come from considerations like these: The XYZ-stuff on twin-earth looks and tastes just like water; it is used in the same way that we use water (brush teeth with it, wash clothes in it, etc.). But what determines the meaning of a physical natural-kind term (it is thought) is its physical make-up, not how it looks or what it's used for.

How it looks and what it's used for "fix the reference" of 'water:' The stuff that looks like *that* (pointing on earth to H2O) and is used for teeth-brushing, etc. is water. It turned out (centuries later) that that stuff is H2O--and it had been H2O all along. Twin-earthians fix the reference of their XYZ-term the same way: The stuff that looks like *that* (pointing on twin-earth to XYZ) and is used for teeth-brushing turned out to be XYZ. Because earthians and twin-earthians use the same descriptions to fix the reference of the relevant terms, it may seem that the Earthian and Twin-Earthian terms for the stuff that looks like water should be the same. But because the descriptions denote different kinds of stuff (H2O and XYZ), the words for the stuffs do not mean the same thing. Twin-Earthians may use a word that sounds like 'water', but it isn't 'water,' since it refers to XYZ.

Philosophers say, 'Water' "rigidly designates" water. That means that in every possible world 'water' refers to what is in fact water in the actual world--i.e., H2O. A world without H2O is a world without water.

It's perhaps worth saying here that there are philosophers whose intuitions are closer to those of the questioner. Gabriel Segal, a member of this panel, has written a nice book called A Slim Book About Narrow Content defending a view not that distant from the one mentioned.

That said, it's important to be clear about what the intuition is supposed to be. As Lynne said (hi, Lynne), the intuition is one about what the term "water" refers to. Or again, the intuition is supposed to be that, if Oscar says, "There's water on twin earth", he speaks falsely. One doesn't have to have that intuition. Some people don't. But before you decide whether you really do, it's worth thinking hard about the fact, mentioned by Lynne, that water is supposed to be a kind of stuff just like gold. Fool's gold isn't gold, no matter how much it looks like gold, and it wouldn't be gold even if it looked a whole lot more like gold, because fool's gold isn't the same kind of stuff that gold is. What we mean by a "kind of stuff" is a hard question, and it's particularly hard as concerns Oscar pre-1850. There are some nice papers by Mark Wilson, e.g. "Predicate Meets Property", on this issue.

The intuitions about the 'water' example that philosophers focus on are, as explained above, about reference. They are also about truth. It takes a little work to connect reference and truth to meaning. One line of thought goes as follows. Suppose that Oscar lands on Twin Earth. Both Oscar and Twin Oscar point to a sample of XYZ and say 'That is water'. What Twin Oscar says is true - he is speaking Twin English and Twin English speakers standardly call XYZ 'water'. But what Oscar says is false. He thinks that the stuff in front of him is water, the same kind of stuff he was familiar with on Earth. And that is the thought he is expressing when he says 'that's water'. But if what Twin Oscar says is true and what Oscar says is false, then their words must mean something different.

I concur with Deniz that non-philosophers often don't respond to the example in the way that many philosophers do - although as yet no seroious data on this have been gathered. Often they either don't share the intuitions about reference and truth or they do, but they remain convinced that what the Twins mean by their words is the same.

As Richard says (thanks for the mention, Richard), I am with the non-philosophers. I think that in 1750 the English word 'water' would have been true of XYZ as well as H2O.

For some discussion of how lay intuitions differ from those of philosophers' in respect of these matters, see my 'Reference, Causal Powers, Externalist Intutions and Unicorns' on my web page.