Twin Earth

Twin Earth is a thought experiment in philosophy that explores how words like "water" refer to things in the world. Imagine a planet identical to Earth, called Twin Earth, where the substance called "water" looks and behaves just like Earth's water, but is made of a different chemical (say, XYZ instead of H₂O). The experiment shows that our understanding of "water" depends not just on its appearance or properties, but also on its underlying chemical makeup and the context of its use. It highlights how meaning is influenced by both language and the world.