Editing Rigid designator (section)

==Necessary identities==
{{see|Necessity of identity}}
One puzzling consequence of Kripke semantics is that identities involving rigid designators are necessary. If [[water]] is H<sub>2</sub>O, then water is ''necessarily'' H<sub>2</sub>O. Since the terms 'water' and 'H<sub>2</sub>O' pick out the same object in every possible world, there is no possible world in which 'water' picks out something different from 'H<sub>2</sub>O'. Therefore, water is necessarily H<sub>2</sub>O. It is possible, of course, that we are mistaken about the chemical composition of water, but that does not affect the [[necessity of identities]]. What is not being claimed is that water is necessarily H<sub>2</sub>O, but ''conditionally'', ''if'' water is H<sub>2</sub>O (though we may not know this, it does not change the fact if it is true), then water is necessarily H<sub>2</sub>O.