A collective noun is a noun that refers to a group. A collective noun itself may be singular or plural, depending on how it is used. When a collective noun is used in a singular sense, it refers to a group as one unified whole or unit. When a collective noun is used in a plural sense, it refers to the individual members or items that may be part of the group but are acting or existing independently.
Singular collective nouns refer to a group as a unified whole or unit. Although there may be many actors in the group, they are functioning as one unit indicated by one collective noun.
The board decides if it is necessary to postpone the project.
A board is made up of many individual board members, but the board members make only one board, which must function, make decisions, and take action as one unit. Therefore, board is a singular collective noun in this example.
The crew dutifully prepares the ship for departure.
The collective noun crew refers to the group of crew members who are all performing a task as a unit.
After the final game of the season, the team usually goes out for ice cream.
The team members go out for a group activity as a unit.
Plural collective nouns refer to the individual members or items that are part of a group but acting as individuals.
The band collected their instruments and went their separate ways.
A band is a group of people, but the members in this sentence are collecting their own things and going their separate ways as individuals.
The crowd scattered and returned to their homes.
The many individual members of the crowd are leaving separately to go to their own homes.
The flock of seagulls fought each other for the last few pieces of bread.
The members of the flock are fighting amongst themselves—every bird for itself.
You may have already noticed that it could be difficult to tell if a collective noun is singular or plural sometimes. Some verbs may be in the same form for singular or plural subjects, and not all sentences contain pronouns or other clues to indicate whether the collective noun in question is singular or plural. For example:
The committee will go out for lunch.
The verb will go out would work here whether committee is singular or plural, and there are no pronouns referring to committee to give us a hint. Thus, from this sentence alone, we have no idea if the committee is going out to lunch together as a group, or if the members all have separate lunch arrangements.
In such cases where you cannot tell from one sentence alone, it is important to look at the context. On the flip side of the coin, it is equally important to be clear and consistent when dealing with collective nouns in your own writing to avoid unnecessary confusion. Imagine getting a memo about a committee meeting with a sentence like the example above. Do you need to make your own lunch plans or not? The frustration!