  The idea has also been deployed in the philosophy of language. Kripke (1980) famously argued that ‘Water is H2O’ is a posteriori but nevertheless a necessary truth, for given that water just is H20, the there is no possible world where THAT stuff is (say) a basic element as the Greeks thought. On the other hand, there is a strong intuition that had the real world been somewhat different from what it is, the odorless liquid that falls from the sky as rain, fills our lakes and rivers, etc. might perfectly well have been an element. So in some sense it is conceivable that water is not H20. Two dimensional semantics makes room for these intuitions by providing a separate dimension that tracks a conception of water that lays aside the chemical nature of what water actually is. Such a ‘narrow content’ account of the meaning of ‘water’ can explain how one may display semantical competence in the use of that term and still be ignorant about the chemistry of water (Chalmers, 2002).