Now, Putnam argues, if we go back to an earlier time, say 1750, and conduct the above experiment when science was not as advanced on either planet as it is say in 1950, then neither planet knew the chemical make-ups of their “waters,” yet they still knew what the term “water” was for their corresponding planets even though they understood what the terms meant differently in 1750 than in 1950 and even though they were still in the same psychological state. Therefore, according to Putnam, the extension of the term “water” is not a function of the psychological state of the speaker by itself (289).
Another example that Putnam posits to strengthen his argument is the elm tree vs. beech tree example. On Twin Earth, a beech tree is the same as an elm tree is on Earth. Therefore, my Doppelganger sees a ‘beech’ tree on Twin Earth, and I see an “elm” tree on Earth, yet we both mean the same thing because we are both seeing the same tree, regardless of what we call it. Therefore, we are both in the same psychological state, which shows that meanings are not in the head (290-291).
Putnam explains that this example depends on the division of linguistic labor. He admits that we wouldn’t be able to use words such as “elm” if we didn’t possess a way of recognizing elm trees, but he goes on to say that just because everyone agrees that the distinction is important doesn’t mean that they have to be able to make that distinction (291). Take the word “car,” for example. I have a car, I know how to drive it, I know how to put gas in it and check the oil to make sure it’s running smoothly, and for the most part, I know when something’s wrong with it that needs fixing; however, I don’t know how to make a car, and I don’t know anything about how to repair one, so if something’s wrong with it and needs fixing, I take it in to an expert, a mechanic, who can fix the problem. Therefore, just because I am not an expert on cars doesn’t mean I don’t need the word “car” in my vocabulary. When a term is subject to division of linguistic labor, the “average” speaker who acquires it does not acquire anything that fixes its extension. In particular, his individual psychological state certainly does not determine its extension; it’s only the sociolinguistic state of the collective linguistic body that the speaker belongs to that determines the extension (292).
Now lets go back to the idea that “intension determines extension.” According to our Twin Earth example, if my foot hurts on Earth, my Doppelganger’s foot hurts on Twin Earth. So, on Earth, I would think to myself, “I feel pain in my foot,” and on Twin Earth, my Doppelganger would think to herself, “I feel pain in my foot.” The extension of the term ‘I’ to me is myself, where the extension of ‘I’ to my Doppelganger is herself. So the same word ‘I’ has two different extensions but it doesn’t conclude that the concept I have of myself is different from the concept she has of herself (294). This refutes the idea that two terms cannot differ in extension and have the same intension.
If we go back to the ‘water’ example on Twin Earth vs. Earth in 1750, although it is not an example of division of linguistic labor because there weren’t any experts on water at this time, we can show that ‘water’ on Twin Earth can only mean the same thing as “water” on Earth because an entity x, in an arbitrary possible world, perhaps Twin Earth, is water if and only if it bears the relation “same liquid as” to the stuff that we call “water” in the actual world, namely Earth (293). Therefore, ‘water’ at another time or in another possible world has to bear the relation to the same liquid as our “water” in order to be water. Thus, the theory that 1) words have “intensions,” or concepts associated with the words by speakers; and 2) intension determines extension—cannot be true of natural-kind words like ‘water’ for the same reason it cannot be true of obviously indexical words like ‘I’ (294).
Putnam concludes that the extension of a term is not fixed by a concept that the individual speaker has in his head, and this is true both because the extension is, in general, determined socially—there is division of linguistic labor as much as “real” labor—and because extension is, in part, determined indexically. The extension of our terms depends on the actual nature of the particular things that serve as paradigms, or ideal examples, and this actual nature not generally fully known to the speaker. Traditionally semantic theory leaves out two contributions to the determination of reference—the contribution of society and the contribution of the real world; a better semantic theory must encompass both (294).
There is one argument that Martinich gives against Putnam’s idea that ‘water’ and “water” have the same meaning on Twin Earth and on Earth, respectively. He says that since they are different liquids, namely XYZ and H2O, what if we were to rename ‘water’ as in XYZ to another name, perhaps ‘quaxel.’ Then quaxel and water would mean the same thing, according to Putnam, even though they were different substances. Although Martinich makes a valid point here, I’m not sure if I agree with the assumption that that’s what Putnam is saying. I think by the water example, he’s not saying that they are the same substance, he’s actually saying the opposite. He’s saying that they have the same name on different planets, but have different definitions, which is true. Furthermore, he’s saying that the only way that Twin Earth’s ‘water’ can mean the same thing as Earth’s “water” is if XYZ was the same liquid as actual Earth’s H2O, which it isn’t. Therefore, I agree with Putnam.
All information taken from Hilary Putnam’s Meaning and Reference paper, pages 288-295 of A.P. Martinich’s The Philosophy of Language, Fourth Edition, 2001.