Here is the single best literary
example I know of Donnellan's distinction, from Kingsley Amis' Girl,
20: Sir Roy Vandervane is explaining to the novel's narrator,
Douglas Yandell, what he sees in Sylvia, his horrible teenage mistress.
`... Another point about her is that she isn't my wife.'
`True. Very few people are Kitty.'
`It isn't Kitty she isn't, you bloody fool. What she isn't is my
wife. Not the same thing at all....'