Plurals are in the mind’s eye

This is a biggie. One of the major bear traps. It’s what is technically known as “concordance of number”: singular subjects require singular verbs and plural subjects require plural verbs. Except when they don’t, naturally…

Dutch is pretty strict about concordance of number: een aantal requires a singular verb because there’s just a single aantal; Ajax requires a singular verb because it’s a single entity, a team; a department remains a singular afdeling no matter how many people are in it. English is much laxer and tends to go with what’s in your mind’s eye – if you’re thinking of lots of individuals, the verb goes plural nevertheless. So the same grammatical subject can take different verb forms! Honestly! The following would be how the majority of native speakers would phrase things:

• Manchester United has enormous debts and is struggling to find a buyer (the corporate entity is in your mind’s eye), but
• Manchester United are playing awfully and have let in five (the players are in your mind’s eye)
• The army is a solid career choice and offers comprehensive training (the insitution is in your mind’s eye), but
• The army are fighting the terrorists and have already captured four (the individual soldiers are in your mind’s eye)
• There are a number of reasons for doing this (your mind’s already progressed to the plural ‘reasons’)
• The staff were up in arms about the new code of conduct (lots of individuals)

I should point out that American English isn’t as flexible as British English here, certainly in relatively formal situations (less so in speech). You will come across things like “the staff is taking a pay cut” and “the coastguard is looking for the boat” there, although it tends to sound a bit hypercorrect to me.

Prevalence: high. And the wrong choice can jar quite badly.
Frequency: endemic. The non-concordant variant is all but unknown. In fact, our Dutch end clients keep trying to tell us we’ve made a mistake.
Native: no. There were attempts by Victorian grammarians to enforce the Dutch-style logic, but it was never natural and now sounds either old-fashioned or plain wrong.