Because of the plurality of areas, it sounds a bit odd to my ears to say "Areas to investigate in the future could be data quality issues or system compatibility". To me, the "be" should rather be "include". Are both correct, and are both common/idiomatic use of English?

I tried searching for it, here and more broadly on the web, but "be" is very broadly used of course. The word coming after it could be anything so I can't do a literal "be [word]" query with quotes, and while the word before is more constrained, "could be" is very commonly used before a single item as well as in other settings, so I couldn't find an answer as to whether it can be used before a list.

  • I don't think it's helpful to include the modal could here. The answers are just the same if you ask whether to say Areas to investigate are x, y, z or Areas to investigate include x, y, z. And you can look up the difference between to be and to include in any dictionary. Commented Jun 27, 2023 at 12:54
  • "Could be" and "could include" mean different things. The latter gives you license to investigate things that aren't in the list.
    – Stuart F
    Commented Jun 27, 2023 at 15:17
  • @FumbleFingers I know the meaning of "be" and that it is not to be used with singulars, but "Areas to investigate in the future could are" is also wrong so I don't see how this could have been found in a dictionary at all.
    – Luc
    Commented Jun 27, 2023 at 15:45
  • @Luc: You misunderstand my point. I'm saying that the modal auxiliary could is irrelevant. Your question asks about whether to use could be or could include - I'm just saying that it would be better if you forgot all about unnecessary could, and asked about whether to use are or include. For which the answer is it depends what you want to say (with or without the irrelevant word could). Commented Jun 27, 2023 at 17:21
  • (We use the "unmarked infinitive form" be after modals like could, but if you remove the unnecessary modal, you need to use a "tensed" verb form - is / are for singular / plural subject.) Commented Jun 27, 2023 at 17:25

1 Answer 1


You can use 'be' before a list. Your breakfast could be bacon, eggs, toast, or muesli. My holiday will be restful, interesting, and expensive. My day trips could be to Carcassonne, Bordeaux, or Biarritz.

You might use 'include' if you want to signify that the list is, or may be, incomplete. My evening activities include watching TV, reading, cooking, and playing cards with my mother. My day trip destinations will include Albi, Narbonne, and Collioure. The implication is that there could be other activities or destinations that I have not mentioned. If I used 'are' instead of 'include', that would make the lists exhaustive.

  • In those examples, "breakfast" and "holiday" are both singular. Saying "My holidays could be to Japan and Norway" (as two separate holiday trips) gives me similar vibes as the "Areas ... could be ..." example. But maybe you're right and it's just the (potential) incompleteness of the list, as emphasised by "could", is what's really bothering me about the sentence :)
    – Luc
    Commented Jun 27, 2023 at 12:01
  • @Luc - see edited answer. Commented Jun 27, 2023 at 12:17
  • 2
    "Areas requiring investigation are X, Y and Z" - a prescriptive list. "Areas to investigate could be..." - a list of suggestions. Commented Jun 27, 2023 at 12:18
  • I should add that my day trip examples were genuine (I've just come back from a week in Toulouse) and my holiday was very restful and interesting, but not really expensive. Commented Jun 27, 2023 at 15:51

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