Full Idea
We should never say 'this' water, but 'something of this sort', and the same goes for everything else that we indicate by means of expressions such as 'that' and 'this'.
Gist of Idea
We should not pick out 'this' water, but only 'something of this sort'
Source
Plato (Timaeus [c.362 BCE], 49d)
Book Reference
Plato: 'Timaeus and Critias', ed/tr. Waterfield,Robin [OUP 2008], p.41
A Reaction
[translation disputed] The point seems to be that 'this' does not say what is being picked out, even with pointing, so the type must be specified. This connects to Geach's claim that identity can only be asserted under some embracing concept.
Related Idea
Idea 12152 Identity is relative. One must not say things are 'the same', but 'the same A as' [Geach]