The basic rule states that a singular subject takes a singular verb, while a plural subject takes a plural verb.
NOTE: The trick is in knowing whether the subject is singular or plural. The next trick is recognizing a singular or plural verb.
Hint: Verbs do not form their plurals by adding an s as nouns do. In order to determine which verb is singular and which one is plural, think of which verb you would use with he or she and which verb you would use with they.
Example:
talks, talk
Which one is the singular form?
Which word would you use with he?
We say, "He talks." Therefore, talks is singular.
We say, "They talk." Therefore, talk is plural.
Rule 1
Two singular subjects connected by or or nor require a singular verb.
Example:
My aunt or my uncle is arriving by train today.
Rule 2
Two singular subjects connected by either/or or neither/nor require a singular verb as in Rule 1.
Examples:
Neither Juan nor Carmen is available.
Either Kiana or Casey is helping today with stage decorations.
Rule 3
When I is one of the two subjects connected by either/or or neither/nor, put it second and follow it with the singular verb am.
Example:
Neither she nor I am going to the festival.
Rule 4
When a singular subject is connected by or or nor to a plural subject, put the plural subject last and use a plural verb.
Example:
The serving bowl or the plates go on that shelf.
Rule 5
When a singular and plural subject are connected by either/or or neither/nor, put the plural subject last and use a plural verb.
Example:
Neither Jenny nor the others are available.
Rule 6
As a general rule, use a plural verb with two or more subjects when they are connected byand.
Example:
A car and a bike are my means of transportation.
Rule 7
Sometimes the subject is separated from the verb by words such as along with, as well as, besides, or not. Ignore these expressions when determining whether to use a singular or plural verb.
Examples:
The politician, along with the newsmen, is expected shortly.
Excitement, as well as nervousness, is the cause of her shaking.
Rule 8
The pronouns each, everyone, every one, everybody, anyone, anybody, someone, andsomebody are singular and require singular verbs. Do not be misled by what follows of.
Examples:
Each of the girls sings well.
Every one of the cakes is gone.
NOTE: Everyone is one word when it means everybody. Every one is two words when the meaning is each one.
Rule 9
With words that indicate portions—percent, fraction, part, majority, some, all, none, remainder, and so forth —look at the noun in your of phrase (object of the preposition) to determine whether to use a singular or plural verb. If the object of the preposition is singular, use a singular verb. If the object of the preposition is plural, use a plural verb.
Examples:
Fifty percent of the pie has disappeared.
Pie is the object of the preposition of.
Fifty percent of the pies have disappeared.
Pies is the object of the preposition.
One-third of the city is unemployed.
One-third of the people are unemployed.
NOTE: Hyphenate all spelled-out fractions.
All of the pie is gone.
All of the pies are gone.
Some of the pie is missing.
Some of the pies are missing.
None of the garbage was picked up.
None of the sentences were punctuated correctly.
Of all her books, none have sold as well as the first one.
NOTE: Apparently, the SAT testing service considers none as a singular word only. However, according to Merriam Webster's Dictionary of English Usage, "Clearly none has been both singular and plural since Old English and still is. The notion that it is singular only is a myth of unknown origin that appears to have arisen in the 19th century. If in context it seems like a singular to you, use a singular verb; if it seems like a plural, use a plural verb. Both are acceptable beyond serious criticism" (p. 664).
Rule 10
The expression the number is followed by a singular verb while the expression a number is followed by a plural verb.
Examples:
The number of people we need to hire is thirteen.
A number of people have written in about this subject.
from :
http://www.grammarbook.com/grammar/subjectVerbAgree.
