[L]et us roll the time back to about 1750. At that time chemistry was not developed on either Earth or Twin Earth. The typical Earthian speaker of English did not know water consisted of hydrogen and oxygen, and the typical Twin Earthian speaker of English did not know “water” consisted of XYZ. Let Oscar1 be such a typical Earthian English speaker, and let Oscar2 be his counter-part on Twin Earth. You may suppose that there is no belief that Oscar1 had about water that Oscar2 did not have about “water” If you like, you may even suppose that Oscar1 and Oscar2 were exact duplicates in appearance, feelings, thoughts, interior monologue, etc. Yet the extension of the term “water” was just as much H2O on Earth in 1750 as in 1950; and the extension of the term “water” was just as much XYZ on Twin Earth in 1750 as in 1950. Oscar1 and Oscar2 understood the term “water” differently in 1750 although they were in the same psychological state, and although, given the state of science at the time, it would have taken their scientific communities about fifty years to discover that they understood the term “water” differently. Th us the extension of the term “water” (and, in fact, its “meaning” in the intuitive preanalytical usage of that term) is not a function of the psychological state of the speaker by itself.