Cannot, can not and can’t are so similar, so does it matter which one you choose? There are differences, so it's important to know when to use each.
Cannot
Cannot is a contraction of the two words can and not. It describes an action as impossible or not allowed. Cannot is most commonly used in formal writing.
For example:
I cannot come out to play until I have finished dinner.
You cannot possibly jump that far.
When describing an action which is impossible, you should always use cannot.
Can not
The words can and not should only appear together when they are part of separate but adjacent phrases. That is, ‘can not’ is part of some other constructions, such as:
not only
but also
For example:
By buying two cakes, Ben can not only have his cake, but eat it, too.
Can’t
Can’t is a contraction of cannot, and is used more informally, particularly when we speak.
For example:
I can’t make it to the end of the race.
I can’t help you with your homework.
