[If you want this as a learning support in Microsoft Word, it’s under that hyperlink.]
The number of the subject determines the number of the verb.
Words that intervene between subject and verb do not affect the number of the verb. (Addendum: The second sentence is the correct one.)
The bittersweet flavor of youth—its trials, its joys, its adventures, its challenges—are not soon forgotten.
The bittersweet flavor of youth—its trials, its joys, its adventures, its challenges—is not soon forgotten.
A common blunder is the use of a singular verb form in a relative clause following “one of…” or similar expression when the relative is the subject. (Addendum: The second sentence is the correct one.)
One of the ablest scientists who has attacked this problem.
One of the ablest scientists who have attacked this problem.
One of those people who is never ready on time.
One of those people who are never ready on time.
Use a singular verb after each, either, everyone, everybody, neither, nobody, someone.
Everybody thinks he has a unique sense of humor.
Although both clocks strike cheerfully, neither keeps good time.
With none, use the singular verb when the word means “no one” or “not one.”
None of us are perfect (Wrong)
None of us is perfect.
A plural verb is commonly used when none suggests more than one thing or person.
None are so fallible as those who are sure they’re right.
A compound subject formed of two or more nouns joined by and almost always requires a plural verb.
The walrus and the carpenter were walking close at hand.
But certain compounds, often clichés, are so inseparable they are considered a unit and so take a singular verb, as do compound subjects qualified by each or every.
The long and short of it is…
Bread and butter was all she served.
Give and take is essential to a happy household.
Every window, picture and mirror was smashed.
A singular subject remains singular even if other nouns are connected to it by with, as well as, in addition to, except, together with, and no less than.
His speech as well as his manner is objectionable.
A linking verb agrees with the number of its subject.
What is wanted is few more pairs of hands.
The trouble with truth is its many varieties.
Some nouns that appear to be plural are usually construed as singular and given a singular verb.
Politics is an art, not a science.
The Republican Headquarters is on this side of the tracks.
The general’s quarters are across the river.
In these cases the writer must simply learn the idioms. The contents of a book is singular. The contents of a jar may be either singular or plural, depending on what’s in the jar—jam or marbles.
Excerpted from: Strunk, William Jr., and E.B. White. The Elements of Style, Fourth Edition. New York: Longman, 2000.