Ever wonder which is more appropriate—“cannot” or “can not”? Really, both are fine, interchangeable, and mean “unable to do” something. However, “cannot” is used far more commonly, and you should use that form in your writing.
The exceptions? You can use “can not” for emphasis: “I can not stand you!”
You can also use “can not” to describe not being able to do something only: “Jane can come to the movies or she can not.” But come on, this is really awkward. You are better off rewriting your sentence for additional clarity: “Jane can come to the movie or she can stay with Jon.”
Another example of “can not”: “If taking the side streets works for you, I can not take the highway as I’d intended.” Again, a rewrite clarifies this sentiment: “If taking the side streets works for you, I won’t take the highway.”
Bottom line: use “cannot” in your writing. Or, do some editing.