Most semantic theories distinguish what we will call purely denotational expressions ("man, blue, walk, day, bachelor") from indexical or deictic expressions ("he, over there, yesterday", the "bachelor"). For an expression to be purely denotational, it must have a fixed sense and denotation. "Bachelor", for example, has a fixed sense, say "unmarried man", and denotes unmarried men in every real or imaginary world.
- Clark & Clark (2004), a pag.147