Cannot vs can not

Found a great article discussing how cannot differ from can not or can't. I only recently had this mistake pointed out to me.

The full article is here (also read the Further Discussion part):
http://alexfiles.com/cannot.shtml

In summary:

cannot: not able to do something. E.g. I cannot swim
can not (or can't): able to to it, but choose not to. For example: I can not study