When the subject is plural, its verb must match or "agree with" it. For example, Dave's friends watch football games.
If writers break this agreement rule, they are judged unskilled.
But sometimes it isn't clear whether the subject noun is singular or plural. In one such exception, the subject is called a collective noun. Take "family." It looks singular. But if the writer means the family as separate individuals, the correct verb may not end in -s: The family watch different TV programs in each of their three living rooms.
Other collective nouns are "team," "staff," and "herd."
In the world of subject-verb agreement, another exception is those plural-looking words that express a singular concept:
The last 12 months has been particularly ugly.
Hear how Yahoo! Groups has changed the lives of others.
The woods is the last place they would go.
Finally, there are the idiomatic pronouns that seem plural in meaning but are used as singulars: Everybody is waiting. Everyone is at home.
Every person is different. All people are different.
I have this many pencils.
In language, custom trumps logic.
