In this exercise we have to complete the space with 4 potential correct answers:

As I am at the dentist. I obviously ____ sign for the package.

a) cannot b) can not c) could not d) did

I have chosen "can not" because of the present conjugation in this sentence. Because your English is better than mine, you might choose "cannot" and that's the reason I want to ask you this question. Why and how?


The only difference between cannot and can not in written English is that the former is for negation only and the later has additional unusual meaning as the ability to not perform some action.

I cannot tell a lie. (I am unable to tell a lie.)
I can not tell a lie. (99% of the time = I am unable to tell a lie. 1% of the time = I am able to not lie.)

In spoken English, we almost always speak the two words as one, "cannot," regardless of how the words would be written.

In your example, either cannot or can not would be entirely appropriate, and nobody would look twice at it in either form. If I had to choose, I would go with cannot, as it reads slightly more fluidly aloud, but that's a really minor distinction between the two forms. They're almost exactly synonymous.

  • What is the difference between 'I am unable to tell a lie' and 'I am able to not lie'? – Rucheer M Sep 18 '15 at 6:28
  • @RuchirM This may help: Professor: "Robot, can you lie?" Robot: "I'm unable to tell a lie. I'm unable to lie." Professor: "Haha! Let me tinker with your robot-brain!" (15 minutes passed) Professor: "I've reprogrammed you to be able to lie. Now, tell me a lie!" Robot: "But, sir. Because I'm still able to not lie, I choose not to lie to you." :-) – Damkerng T. Sep 18 '15 at 7:49
  • @RuchirM My example is far less sophisticated, but imagine a man and a woman talking. Woman: "Men can't resist looking at every beautiful women they see." Man: "That's absurd, I can not look at a beautiful woman." This doesn't mean that he is unable to look at beautiful women, instead it means that he can control himself, he has the ability to not look. – Jason Patterson Sep 18 '15 at 20:20

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