Mind: A Brief Introduction (John R. Searle) / quote 127 of 138
Meanings just ain't in the head
You might think that “water” could be defined as a clear, colorless, tasteless liquid found in lakes and streams and coming out of the sky in the form of rain. But, says Hilary Putnam, that does not give the meaning of “water.” To see this, imagine a galaxy just like ours, with a planet in it just like our planet, that we will call Twin Earth. On Twin Earth everything is exactly the same as it is on Earth, molecule for molecule, with one exception. What we on Earth call “water” is made of H2O; what people on Twin Earth call “water” is not H2O but has a very long chemical formula that we can abbreviate as “XYZ.” Now, in 1750, before anybody knew anything about chemical composition, what was in the heads of the Twin Earth people when they used the word “water” was exactly the same as what was in the heads of the Earth people when they use the same word. But all the same, though the contents of the heads were the same, the meanings were different. Meanings cannot be in the head, because the same things are in their heads as are in our heads, but the meanings are different. “Water” on Earth refers to one kind of stuff; “water” on Twin Earth refers to another kind of stuff. The meaning on both Earth and Twin Earth, says Putnam, is determined by causal relations in which speakers stand to indexically presented substances. “Water” on Earth means whatever has the same structure as this indexically presented stuff. Ditto for Twin Earth. But since the stuffs are different, H2O in one case, XYZ in the other, the meanings are different. Meanings, concludes Putnam, “just ain’t in the head.”4 What goes for meaning goes for mental content generally. Beliefs employing the expression “water” are different for the people on Twin Earth than for the people on Earth. But if so, it turns out that beliefs cannot be entirely in the head. What is in the head is exactly the same in the two cases, though the beliefs are different.