This is quite a long and technical post so I have divided it into three sections (What; Which and why; So) and have included a lot of examples.
What
Nouns of multitude are wholes that comprise similar parts. They are a type of collective noun; examples include committee, team, government, jury, Ministry, army, group, party, crowd, flock, generation, mob, staff, department, family, crew, clergy, herd, syndicate, faculty, audience, public, company, Congress, orchestra, firm, and Parliament.
There is confusion over whether nouns of multitude are singular (the collective entity) or plural (the individuals in it). In fact they are both, or rather they can be either. This ambiguity means that there are better and worse ways to use them – but there is no definitive right and wrong way. To tease out the details we must look more closely at how they are used.
When using nouns of multitude with verbs and pronouns, the main thing is to be consistent. The following examples are not:
After the jury returns with their verdict…
The committee has agreed that after their AGM next week…
These lines are missing what is known as “notional agreement” or “notional concord”. They are unlikely to bother the casual reader, but they are likely to be revised in edited prose. More conspicuously aberrant is an example I read over the weekend:

From: Ireland crowned grand slam champions, RTÉ News, 21 March 2009. The Minister’s original statement (“They are deserving winners…”) was fine; RTÉ introduced the incongruence of making team both singular and plural in the same clause.
Which and why
So if a noun of multitude can be singular or plural, which should it be, and why? The team was, or the team were? The jury finds, or the jury find? Your decision depends first on whether you are writing American or British English. The plural form is more common in BrE (The press have reacted swiftly), though the singular form is also standard (The Government anticipates). The singular form is more common in AmE (The press has reacted swiftly). But these are mere generalities; there is considerable variation.
Your decision also depends on what you want to emphasise. To stress a group’s plurality, use the plural; to stress the group as a unit, use the singular:
The department is prepared for cutbacks (the department as a whole is prepared)
The department are to be praised for their efforts (all individuals in the department deserve praise)
Sports teams usually take the plural in British English (the team were deserving winners; Liverpool are beating United), but in business contexts and AmE they can just as suitably take the singular (Manchester United is a wealthy club; Baltimore beats Browns).
If you are still unsure, a pronoun might help you decide. You would not write: “the board fought among itself” because it takes at least two to fight; this implication immediately suggests the plural: “The board fought among themselves”. (It’s easier to succumb to contradictions when speaking than when writing, and easier to ignore contradictions when listening than when reading.)
So
With these conventions and principles in mind we look again at earlier examples:
After the jury returns with their verdict…
Singular and plural forms (returns and its, or return and their, respectively) are both standard in BrE; the singular form dominates in AmE. Both are fine.
The committee has agreed that after their AGM next week…
The singular (has and its) is acceptable, but suggests a unit agreeing with itself, whereas the plural (have and their) suggests round-the-table agreement by all the members of the committee. This connotation makes the plural the better choice. Subtle distinctions sometimes accompany the verb, and might help you decide whether singular or plural is preferable.
If it doesn’t clutter your syntax, you can elaborate for the sake of accuracy and clarity, e.g. by referring to the Cabinet as the Cabinet members, or the members of the Cabinet, both of which are plainly plural. This tactic is less likely to work if the collective noun appears frequently, because it would lead to the aforementioned clutter. And you won’t see it in a headline, where concision is paramount.
Finally, using a collective noun as both singular and plural in the same context is inadvisable if you want to maintain notional agreement, but in casual or colloquial usage it presents no problem. To borrow an example from Eric Partridge’s Usage and Abusage:
The family is well and send their regards.
The family as a whole is [are] well, and the people in it send their regards. Were the family to send its regards, it would seem less personal.