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I read on news that

... such checks are a must for ...

why is the plural subject here followed by "a", a singular determiner?

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  • Welcome to ELU. Look up the meanings for must in a good dictionary. Let us know if you still have any questions. Good Luck.
    – Kris
    Sep 16, 2019 at 9:45
  • People are a mystery. Nothing says both halves of a copula must be the same number. That one wasn't.
    – tchrist
    Sep 17, 2019 at 1:19
  • Consider: a dozen eggs.
    – tchrist
    Sep 18, 2019 at 0:08

1 Answer 1

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The short answer: because a must is a fixed idiom.

But we could replace it with a requirement, if the checks are considered collectively: what is required is not each check separately, but the practice of making such checks.

We say “these people are a family” without worrying about the number.

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