In this video (at 3:43) some guy told me that I can't use 'could' to talk about negative possibilities. Is it true? If so, why?


They might not be ready.

He may not be able to help you.

The guy said that there is no way to use 'could' in these sentences.

closed as unclear what you're asking by Janus Bahs Jacquet, jimm101, J. Taylor, Rand al'Thor, Mari-Lou A Feb 16 at 21:34

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  • Please edit your question to make it clearer what exactly you’re asking. What is a negative possibility? Please provide an example sentence to show what type of context you’re asking about. – Janus Bahs Jacquet Feb 12 at 19:15
  • Could? (with a question mark)...it shows doubt. – user22542 Feb 12 at 19:41
  • Could you clarify what you mean? – Oleksiy Plotnyts'kyy Feb 12 at 19:45
  • That's a long video. Please say at what time he says that. As native speakers we don't want to listen to the whole thing. Thanks. – chasly from UK Feb 12 at 19:45
  • If you use 'could [not]', you automatically get an impossibility (A was not possible), as opposed to a 'negative possibility' (not-A is possible). – We oath to creation Feb 12 at 19:48

Note: This question was changed after I answered it. Originally, it had only been asking about could, not could not.

I see no reason why you can't recast both of those sentences to use could while preserving their meaning:

They might not be ready.
🠆 They could be unprepared.

He may not be able to help you.
🠆 He could be unable to help you.

We replace might not or may not with could, and replace the positive statement with a negative statement (be ready becomes be unprepared and be able to becomes be unable to).

Something similar can also be done with could not:

They might not be ready.
🠆 They could not necessarily be ready.

He may not be able to help you.
🠆 He could not necessarily be able to help you.

Here, the last part of the sentence remains in the positive.

  • Yes, but if we use exactly "could not" the meaning becomes different, doesn't it? – Oleksiy Plotnyts'kyy Feb 13 at 9:52
  • @OleksiyPlotnyts'kyy See my updated answer. – Jason Bassford Feb 13 at 14:39
  • 1
    The example that comes to mind for me is an exchange of this kind: "I could do <some ill-advised thing>" followed by "Or you could not do <ill-advised thing>." If spoken, the "not" would be emphasized. – user888379 Feb 13 at 21:55

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