There exists a twin Earth that is in every respect the same as Earth but except but we call water or H2O, they call XYZ.
My twin on this planet is thinking of XYZ and I am thinking of H2O.
Line of argumentation:
- Content determines object
- If thought 1 and thought 2 have different objects, then they must also have different content
- Twin and I have thoughts with different content
- Thoughts are individuated by their content
- Twin and I have different thoughts even though we are molecule-for-molecule duplicates
Thus, even though water is in all worlds, but ‘water’ doesn’t mean the same thing in and