Hilary Putnam: The meaning of 'meaning'. In: Minnesota studies in the philosophy of science 7: Language, mind and knowledge. hg. von Keith Gunderson. - Minneapolis : University of Minnesota Press, 1975, 131-193, hier 139-141. https://conservancy.umn.edu/handle/11299/185225
»Are meanings in the head? That psychological state does not determine extension will now be shown with the aid of a little science fiction. For the purpose of the following science-fiction examples, we shall suppose that somewhere in the galaxy there is a planet we shall call Twin Earth. Twin Earth is very much like Earth; in fact, people on Twin Earth even speak English. In fact, apart from the differences we shall specify in our science-fiction examples, the reader may suppose that Twin Earth is exactly like Earth. […] One of the peculiarities of Twin Earth is that the liquid called „water“ is not H20 but a different liquid whose chemical formula is very long and complicated. I shall abbreviate this chemical formula simply as XYZ. I shall suppose that XYZ is indistinguishable from water at normal temperatures and pressures. In particular, it tastes like water and it quenches thirst like water. Also, I shall suppose that the oceans and lakes and seas of Twin Earth contain XYZ and not water, that it rains XYZ on Twin Earth and not water, etc.
If a spaceship from Earth ever.visits Twin Earth, then the supposition at first will be that „water“ has the same meaning on Earth and on Twin Earth. This supposition will be corrected when it is discovered that „water“ on Twin Earth is XYZ, and the Earthian spaceship will report somewhat as follows: „On Twin Earth the word 'water' means XYZ.“ […] Symmetrically, if a spaceship from Twin Earth ever visits Earth, then the supposition at first will be that the word „water“ has the same meaning on Twin Earth and on Earth. This supposition will be corrected when it is discovered that „water“ on Earth is H20, and the Twin Earthian spaceship will report: „On Earth the word 'water' means H20.“ […] Now let 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 XY2. Let Oscar1 be such a typical Earthian English speaker, and let Oscar2 be his counterpart 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 Oscar 2 were exact duplicates in appearance, feelings, thoughts, interior monologue, etc. Yet the extension of the term „water“ was just as much H20 on Earth in 1750 as in 1950; and the extension of the term „water“ was just as much XY2 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. Thus 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.«
Man stelle sich vor, es gäbe eine Zwillingserde, die unserer Erde in jeder Hinsicht gleicht, nur dass es dort kein HZweiO in Flüssen und Seen gibt, sondern eine andere klare, geschmacks- und geruchslose Flüssigkeit, deren komplizierte chemische Struktur mit XYZ abgekürzt wird. XYZ wird von den Zwillingserde-Bewohnern auch 'Wasser' genannt. Stellen wir uns vor, dass sich ein Erdling und ein Zwillingserdling treffen zu einem Zeitpunkt, als beide Planeten noch nicht die technischen Möglichkeiten haben, chemische Verbindungen aufzudecken. Hat für beide das Wort „Wasser“ (das auf der Erde HZweiO und auf der Zwillingserde XYZ bezeichnet) dieselbe Bedeutung, wo sie doch die gleichen Gedanken dazu haben? Die Antwort ist „nein“: denn die Wortbedeutung hängt auch vom Bezeichneten hab, und das ist verschieden, ob die beiden das wissen oder nicht.