How do you explain the difference between "Cannot" and "Can not"?
When do we use which? Thanks.

The Oxford dictionary explains this very well. Here's a link to their entry for "cannot".

http://www.oxforddictionaries.com/definition/english/cannot



PaulM

Incidentally, one thing that the Oxford Dictionary omits to mention is that you must use the negative form "can't" in pre-subject position:

"Can not/ Cannot / Can't we stay a little longer.

According to my knowledge and the oxford dictionary, "Cannot" should be used always for normal sentences and "Can not" should be used for very few sentences which include articles. I don't believe in "can not" because I think using one word instead of two is better and much more thoughtful!

That's only partly true, Daniella.

The word sequence "can not" is sometimes used for emphasis:

I simply can not believe it!

And sometimes "can not" is required in comparative constructions:

He can not only dance, but he can sing as well!

Note also that the negative form "can't" is more common then "cannot" in speech; indeed it is compulsory when it precedes the subject:

Can't / Cannot / Can not we stay a little longer?


By the way, I gave a link to the Oxford's entry for "can not" in my first answer.


PaulM