Is there a particular reason that we should write 'cannot, and not 'can not'?
This may be one of those hope-not-to-have-gotten-pedantic questions!
It's just a matter of style and usage habits rather than any particular thing ordained by the syntax or orthography of the language. Merriam-Webster's Dictionary of English Usage has a good entry about it.
Actually it can make a difference. Â If I write "I can not do that", I may mean that I am unable to do it, or that I am able to not do it. Â So I (with my habitual horror of ambivalence) always use "cannot" when I mean the former.
It's probably connected with the inconsistency in indefinite pronouns:
everything, anything, something, nothing
everybody, anybody, somebody, nobody
everyone, anyone, someone, no one
Why is no one the only one that can't be a single word?
Ron Draney said
Why is no one the only one that can't be a single word?
I have wondered that my self many times. Â The only answer I ever got was that it would look like noon and cause a pause in reading. Â It makes sense but I don't know if that was the original reason.