I hear that:

  1. That must not be Toby! - correct

  2. That must be not Toby! - doesn't make sense

Do you agree?

  • 1
    The first could be a colloquial and jokey way to say "I hope that isn't Toby". The second doesn't make sense. Oct 16, 2020 at 23:53
  • Any explanation why it's wrong?
    – user1425
    Oct 17, 2020 at 5:02
  • See my answer below. Oct 17, 2020 at 10:01

1 Answer 1


As FumbleFingers said, "negation is complex". It is especially so when tied up with the evolution of English and with gerunds.

At the time of the King James Bible "Be not" was colloquial: "Be not afraid", for example, where today we'd say "Don't be afraid"; or "If it be not Toby", where today we'd say "If it isn't Toby." Googling "Be not" returns mostly examples of its usage dating from the 16th to the 18th century, together with discussions about English grammar, many of them here on StackExchange!

If, today, it was idiomatic to say "That must be not Toby" then it would also be idiomatic to say "That be not Toby" and "That be Toby". We don't. We say "That is Toby", "That is not Toby" and "That must not be Toby!"

This - on the use of the present subjunctive- might be helpful.

  • Would you approve of this: That must be not Toby but Bob!
    – user1425
    Oct 17, 2020 at 10:26
  • In conversation you can say what you like! It isn't a grammatically-correct sentence though, because it's broken in the middle. We don't say "That must be not". We might say, "That must be - not Toby, but Bob" , with a break in the middle to show we know the sentence is broken. We'd usually say "That can't be Toby: it must be Bob. or "That must be Bob, not Toby." Oct 17, 2020 at 13:17

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