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Can Not or Cannot?

The Quick Answer
Cannot (one word) is the most common expansion of the contraction can't.

Can't can also be expanded to can not (i.e., two words), but this is less common and usually reserved for emphasis. For example:
  • I cannot do it!
  • (Can't is usually expanded to cannot.)
  • I can not do it!
  • (This is considered more emphatic.)
Of course, the words can and not sometimes appear alongside each other when the not forms part of another construction (such as not only). For example:
  • Kevin can not only rap but dance too.
  • (Here, can not must be written as two words. It is not an expansion of can't.)

Cannot or Can Not?

Cannot and can not are interchangeable as expansions of the contraction can't. However, the modern preference is to use cannot. Of note, many spellcheckers even highlight can not as an error.

Examples with Cannot and Can Not

Here are some famous quotes featuring cannot and can not.
  • You cannot escape the responsibility of tomorrow by evading it today. (Abraham Lincoln)

  • There cannot be a crisis next week. My schedule is already full. (Henry A. Kissinger)

  • Conflict can not survive without your participation.  (Wayne Dyer)
  • (We have marked this wrong because can not is not the modern convention.)

  • A flower cannot blossom without sunshine, and man cannot live without love. (Max Muller)

  • Three things cannot be long hidden: the sun, the moon, and the truth. (Buddha)

Can Not for Emphasis

You should use can not over cannot when the not is emphasized. For example:
  • I can not tolerate laziness!
  • (The two-word version makes it clearer that the word not should be emphasized. This is most useful in an exclamatory sentence, i.e., one that ends in an exclamation mark.)

Sometimes You Must Use Can Not

It is possible to see can and not as two separate words, especially with the correlative conjunction not only...but also.
  • Danielle can not only cook but also bake.

  • My dog can not only roll over but also play dead.

  • I like that people who are not experts can not only understand but also become engaged by my work. (Leslie Fiedler)

  • A very quiet and tasteful way to be famous is to have a famous relative. Then you can not only be nothing, you can do nothing too. (P. J. O'Rourke)
In these examples, cannot is not an option.
Interactive Test
 
 
Beware

Put the Apostrophe in the Correct Place

If you're using the word cannot, you can shorten it to can't. Make sure you put the apostrophe in the correct place.

cannot can not
(This is an apostrophe error found in a Christmas cracker. If you make a mistake like this, people will laugh at you not with you.)