The brilliant Letters of Note blog has reproduced a nice letter CS Lewis (author of the Chronicles of Narnia, among my favourite books when I was little) sent to a young fan. In it, he gives her advice about writing. He critiques hers specifically, and then goes on to answer some questions she had about grammar:
About amn’t I, aren’t I and am I not, of course there are no right or wrong answers about language in the sense in which there are right and wrong answers in Arithmetic. “Good English” is whatever educated people talk; so that what is good in one place or time would not be so in another. Amn’t I was good 50 years ago in the North of Ireland where I was brought up, but bad in Southern England. Aren’t I would have been hideously bad in Ireland but very good in England. And of course I just don’t know which (if either) is good in modern Florida. Don’t take any notice of teachers and textbooks in such matters. Nor of logic. It is good to say “more than one passenger was hurt,” although more than one equals at least two and therefore logically the verb ought to be plural were not singular was!
Sensible advice from a very clever man.