I used to write 'can not'. But a website like grammarly correct it to 'cannot'. I am confused which one to use?

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    This has nothing to do with grammar or grammaticality. It only has anything to do with spelling, which is orthogonal to grammar.
    – tchrist
    Jun 3, 2021 at 18:16

2 Answers 2


According to Oxford Dictionaries, both of them are acceptable:

Both cannot and can not are acceptable spellings, but the first is much more usual. You would use can not when the ‘not’ forms part of another construction such as ‘not only’. For example:

  • These green industries can not only create more jobs, but also promote sustainable development of the land.

I also found this post from Grammarly blog:

  • Can’t is a contraction of cannot, and as such it’s sometimes unsuitable for formal writing. In everyday writing and in speaking, it’s ubiquitous:

  • Cannot is better for formal writing.

  • Don’t use can not when you mean cannot. The only time you’re likely to see can not written as separate words is when the word “can” happens to precede some other phrase that happens to start with “not”

  • I would add that in ordinary speech, if the 'not' is to be emphasised then we might see the following exchange. John: I can't. Mary: Yes you can. John: I can NOT! Nov 1, 2018 at 23:36
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    There is another problem with using can not. A possible sense means "I am capable of not doing it." For example, "I'm an alcoholic but I can not drink if I really put my mind to it." This is an unusual sense, but it's still perfectly valid. Whenever I read "can not" I'm always reminded of it—and also the fact that the actual meaning can be ambiguous if the sentence isn't constructed to avoid it. Nov 1, 2018 at 23:54

My go-to sentence to understand the difference:

  • This dog cannot bark: It is mute, has lost its voice.
  • This dog can not bark: It is capable of barking (and often does), but sometimes, it is able to shut up as well.

Very similar to @jasonbassford's comment.

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