Cannot vs. Can not

You'll use cannot when can is an absolute impossibility. For example:

I cannot go to the party in Minneapolis in an hour because I am currently in Virginia.

You'll use can not (two words or can't) when can is a possibility. For example:

I can not go to the store now, but I can in an hour.

Also: I can't go to the store now, but I can in an hour.

Now you know which wins when with cannot vs. can not.