Quote Originally Posted by emsr2d2 View Post
As a BrE speaker, I was trying to find any subtle difference between my use of the two different constructions. Much of the time, I think they're interchangeable but I did come up with one example:

A friend says to me "Peter is going to London on Saturday but of course he has to go on the train".

I don't know why he has to go on the train so I would ask a question to try to find out.

Question 1 - "Can he not drive?" By this I would probably mean "Does he not have a driving licence?" (is he legally not able to drive?)

or

Question 2 - "Can't he drive?" This would mean "Is there some reason why he can't go by car that day?" For instance, has his car broken down? Is someone else using the car that day?

I can't honestly say that this is a hard and fast rule that I would stick to.

As far as the original examples go, I would probably hear a slightly different meaning:

Isn't it a nice day?! - This is an exclamation - you have looked out the window, or been outside and discovered that the weather is beautiful so you say this, as a somewhat rhetorical question.

Is it not a nice day? - You thought it was a nice day but then someone else told you that they had just come in and it was now raining. You would say "Oh, is it not a nice day (any more)?" as a result.
***** NOT A TEACHER *****

Good morning, Emsr.

(1) Thank you for your intriguing examples. I shall study them very carefully.

(2) I stumbled across a scholarly paper on the Web that discusses this matter.

(3) The author used another example, but if I understood her correctly (a big IF), she might explain your "fine day" sentence in this way:

It is a fine day.

Is it a fine day?

It isn't a fine day.

Isn't it a fine day?

Is it not a fine day?

*****

She says that in "Isn't it a fine day?" NOT negates the whole sentence; But in "Is it not a fine day?" NOT negates part of the sentence ("a fine day"???).

Thus, your "a fine day" sentences seem to confirm her theory.

Thanks SO much for your insight.

Have a FINE day!