Basic Rule. A singular
subject (she, Bill, car) takes
a singular verb (is, goes, shines),
whereas a plural subject takes a plural verb.
Example:
The list of items is/are on the desk.
If you know
that list is the subject, then
you will choose is for the
verb.
Rule 1. A subject
will come before a phrase beginning with of.
This is a key rule for understanding subjects. The word of is the culprit in many, perhaps most, subject-verb mistakes.
Hasty writers,
speakers, readers, and listeners might miss the all-too-common mistake in the
following sentence:
Incorrect: A bouquet of yellow roses lend color and
fragrance to the room.
Correct: A bouquet of yellow roses lends
. . . (bouquet lends, not roses lend)
Rule 2. Two
singular subjects connected by or,
either/or, or neither/nor
require a singular verb.
Examples:
My aunt or my uncle is arriving by train today.
Neither Juan nor Carmen is
available.
Either Kiana or Casey is helping today
with stage decorations.
Rule 3. The verb in
an or, either/or, or neither/nor sentence agrees with the
noun or pronoun closest to it.
Examples:
Neither the plates nor the serving bowl goes on
that shelf.
Neither the serving bowl nor the plates go on that
shelf.
This rule
can lead to bumps in the road. For example, if I is one of two (or more) subjects, it could lead to this odd
sentence:
Awkward: Neither she, my friends, nor I am going to
the festival.
If possible,
it's best to reword such grammatically correct but awkward sentences.
Better:
Neither she, I, nor my friends are going to the festival.
OR
She, my friends, and I are not going to the festival.
Rule 4. As a
general rule, use a plural verb with two or more subjects when they are
connected by and.
Example:
A car and a bike are my means of transportation.
But note
these exceptions:
Exceptions:
Breaking and entering is against the law.
The bed and breakfast was charming.
In those
sentences, breaking and entering
and bed and breakfast are
compound nouns.
Rule 5a. Sometimes
the subject is separated from the verb by such words as along with, as well as, besides, not, etc. These words and
phrases are not part of the subject. Ignore them and use a singular verb when
the subject is singular.
Examples:
The politician, along with the newsmen, is expected
shortly.
Excitement, as well as nervousness, is the cause of her shaking.
Rule 5b. Parentheses
are not part of the subject.
Example: Joe (and his trusty mutt) was always welcome.
If this
seems awkward, try rewriting the sentence.
Rule 6. In
sentences beginning with here
or there, the true subject
follows the verb.
Examples:
There are four hurdles to jump.
There is a high hurdle to jump.
Here are the keys.
Rule 7. Use a
singular verb with distances, periods of time, sums of money, etc., when
considered as a unit.
Examples:
Three miles is too far to walk.
Five years is the maximum sentence for that offense.
Ten dollars is a high price to pay.
BUT
Ten dollars (i.e., dollar bills) were scattered on the
floor.
Rule 8. With words
that indicate portions—e.g., a lot, a
majority, some, all—Rule 1 given earlier in this section is reversed,
and we are guided by the noun after of.
If the noun after of is
singular, use a singular verb. If it is plural, use a plural verb.
Examples:
A lot of the pie has disappeared.
A lot of the pies have disappeared.
A third of the city is unemployed.
A third of the people are unemployed.
All of the pie is gone.
All of the pies are gone.
Some of the pie is missing.
Some of the pies are missing.
Rule 9. With collective
nouns such as group, jury, family, audience,
population, the verb might be
singular or plural, depending on the writer's intent.
Examples:
All of my family has arrived OR have
arrived.
Most of the jury is here OR are here.
A third of the population was not in favor
OR were not in favor of the bill.
Rule 10. The word were replaces was in sentences that express a wish or are
contrary to fact:
Example: If Joe were here, you'd be sorry.
Shouldn't Joe be followed by was, not were, given that Joe is singular?
But Joe isn't actually here, so we say were, not was. The sentence demonstrates
the subjunctive mood, which is used to express things that are
hypothetical, wishful, imaginary, or factually contradictory. The subjunctive
mood pairs singular subjects with what we usually think of as plural verbs.
Examples:
I wish it were Friday.
She requested that he raise his hand.
source
http://www.grammarbook.com/grammar/subjectVerbAgree.asp
