Ugh. . . I can not choose to proofread my comments before I post, but then I cannot prevent spelling and grammatical errors in my work.

Can not and cannot have 2 different meaning. You have the ability to not do something, which is where you would use "can not", for example "I can not choose to be a jerk, and I an choose to be nice." The word "cannot" indicates impossibility. I cannot life a building.

While it is possible for "can not" and "cannot" to be used to mean the same thing, (I can not eat this food vs I cannot eat this food), it is MUCH simpler to use "cannot" in terms of impossibility, and "can not" when there is a decision to be made on the issue in question.