I remember being told the modal “need” is used only in interrogative and negative sentences and was for quite a long time more idiomatic than the normal forms, but is there anything wrong with the following examples, in which “need” can seemingly be replaced with “must”?

  1. All you need do is ask.
  2. He wonders if he need go.
  3. In order to pass the course you need pass the exam.

Is the only crime here some awkwardness, or are these ungrammatical?

Thank you!

  • 1
    Semi-modal need and dare are negative polarity items; that is, they can only occur in negative environments, which includes questions and if clauses. That explains why (1-2) are grammatical. (3) is ungrammatical, however, since that clause isn't a negative environment. Commented Jul 28, 2020 at 0:06
  • @JohnLawler Thank you, I had never heard of “negative polarity items,” but the first isn’t a question, so does the pronoun “all,” because it means “the only thing,” introduce a negative environment? Commented Jul 28, 2020 at 0:16
  • So I can write, “In order to pass the course you need only pass the exam,” but have to find another word for example three above? Commented Jul 28, 2020 at 0:30
  • 1
    Yes, only is a negative trigger. But adding only changes the meaning somewhat. Commented Jul 28, 2020 at 2:15


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