Good morning, TheParser and billmcd. Thank you for your replies!
I was told that:
Can't he drive?= He can drive, can't he? (The asking person knows that HE is able to drive, but the asking one just wants to confirm that further and wants a positive answer, 'YES, HE CAN')
Can he not drive?=The asking person actually doesn't know whether HE can drive or not. The asking one only wants to make sure.
Does such saying make sense to you, native speakers?:?:
(After reading my grammar books, I created the followings. However, I'm not sure whether my understanding is right or not?

)
Isn't it a fine day?
Let's say, on a SUNNY day, A wanted to invite B to go for a baubecue, but B was unwilling to and made an excuse:
B:Oh, that's a good idea, but you see it looks as if it is going to rain!
A:Isn't it a fine day? (In fact, it's sunny outside.)
B:Er...
Is it not a fine day?
One morning, in a bedroom with a curtain closed, A was still in bed. Just then A heard B say: (A did not know what the weather was like.)
B:It's raining again!
A:Is it not a fine day?
B:No, it isn't. We have to call off our picnic.
Dear all, is my understanding right? Looking forward to everyone's reply!