cannot, can not

Both cannot and can not are correct. However, cannot is the far more common spelling and should be used in most cases.

We recommend the following guidelines.

Single word

Use cannot in most cases when the meaning is “be unable to”:

• Ted cannot (is unable to) find his keys.
• The parties cannot (are unable to) agree.
• Erica cannot (is unable to) play at the jazz festival.

Note: The contraction is can’t.

Two words

Use can not when you want to give particular emphasis to the word not:

• No, Mr. Smith can not use the company car. His licence has been suspended.
• Erica can not reach a speed of 75 km per hour on her bike! I refuse to believe such an absurd claim!

Use can not when the word not belongs with a separate structure:

• Jessica can not only add but also multiply large numbers in her head.
  [not is part of the expression not only…but also]
• Abdul can enter the contest, or he can not enter it, as he likes.
  [not belongs with enter: can not enter = is able to not enter]

OR

• Abdul can enter the contest or not, as he likes.