Contemporary Debates on Semantic Externalism

Building directly on Kripke's causal theory of reference for natural-kind terms, the American philosopher Hilary Putnam (1926–2016) advanced a parallel and equally influential argument for semantic and mental externalism in his 1975 essay "The Meaning of 'Meaning,'" published in the volume Minnesota Studies in the Philosophy of Science. Putnam's celebrated thought experiment imagines a planet called Twin Earth, a molecule-for-molecule duplicate of Earth in every respect save one: on Twin Earth, the clear, drinkable liquid that fills its lakes and rivers, and that Twin Earth speakers call "water," is not H2O but a different chemical compound, superficially indistinguishable from water, which Putnam abbreviates as XYZ. Putnam asks readers to consider a time, before the chemical structure of either liquid was known — say, 1750, before Lavoisier and Cavendish's determination of water's composition — when an Earth speaker and their molecule-for-molecule identical Twin Earth counterpart would have had qualitatively indistinguishable mental states regarding "water," yet Putnam argues that the Earth speaker's term "water" already referred to H2O and the Twin Earth counterpart's term "water" already referred to XYZ, even though neither speaker could have told the difference introspectively.