In my post on Subject Verb Agreement I had already mentioned this rule. On request from many students, I am explaining this particular concept in detail.
A collective noun is a noun that represents a group or a collection of objects usually considered as a unit. Words like crowd, troop, herd, people, flock, and jury are collective nouns.
A collective noun that is singular in meaning requires a singular verb. A collective noun that is plural in meaning requires a plural verb.
If the collective noun in a particular sentence represents the individuals acting as a unit, the noun is singular. If the sentence indicates clearly that the individuals are acting seperately, the noun is plural.
1). The committee is opposed to the plan. (acting as a unit)
2). The board of directors is in session. (as a unit)
3). The jury returned its verdict. (as a unit)
4). The jury have returned to their homes. (as individuals)
5). The family have given their contributions. (as individuals)
In most cases where the individuals composing a group are acting seperately, it is better to use such expressions as the members of the jury, the members of the family, etc. These expressions sound better and clearly indicate that the individuals are acting seperately.
1). The members of the jury have returned to their homes.
2). The members of the band wore their uniforms.
3). The people in the audience waved their hands.