One of the items on my proofreading checklist is subject-verb agreement.

What’s wrong with this sentence?

The boats’ sails is too small for me to see properly.

The verb doesn’t match the subject and, in most cases, both need to be either plural or singular.

The boats’ sails are too small for me to see properly.

With a collective noun, if members of a group are acting separately, it uses a plural verb.

A few members of the family are meeting next week. 

Similarly, if the subject of a sentence is made up of more than one noun using and, it uses a plural verb.

The moon and the stars are very bright.

If the subject is made using or or nor and a mix of singular and plural nouns, the verb agrees with the nearest noun.

Neither the streetlights nor the moon is visible through the trees.

With sentences beginning there is or there are, the subject agrees with the singular verb is or plural verb are. 

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