Putnam’s (1975a) Twin Earth thought experiment, in a non-semantic guise, leads to a similar conclusion. We imagine there is a planet, ‘Twin Earth’, exactly like Earth in all readily observable respects. Every person and thing on Earth has a twin equivalent on Twin Earth. However, there is no H2O on Twin Earth. Instead, there is a liquid that shares the manifest properties of water (e.g., its being colourless, tasteless, odourless, good for drinking, etc.). This liquid is composed not of H2O mole