Should the copulative verb be singular or plural in this type of sentence:

A crucial question is / are the causes of misunderstandings ?

  • 1
    I think it's General Reference that the grammatical subject here is "a crucial question" - which is singular, so it requires a singular verb form. Aug 14, 2014 at 20:57
  • 1
    You’ll also want to have number agreement between “question” and “cause”. Aug 14, 2014 at 22:54
  • 2
    I would revise to write "A crucial question is one that causes misunderstandings." That sounds better to me, if you are definite crucial question and it avoids the dubious verb form. (I didn't look up a rule, but "is" and "are" both sound a little off in your example, which is why I suggest revising it entirely.) You could also write simply "Crucial questions cause misunderstandings." Aug 14, 2014 at 23:22

1 Answer 1


I would say:

A crucial question is what are the causes of misunderstanding(s)?

is matches question and are matches causes.

What are the causes of misunderstanding(s)?

becomes the crucial question.

Also I would consider misunderstanding as uncountable, but that may just be me.

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