While grammar is not as static a science as is typically assumed, there are 20 rules of subject verb agreement that attempt to objectify part of the English language form. Most of the concepts of subject verb agreement are straightforward, yet some aspects of singular and plural usage in English grammar are more complicated.
Consider the second person plural pronoun "y'all" as it's used in the southern American dialect, for example. Addressing a group of people in the second person using standard English is inefficient and requires more words.
A sentence like "I want to talk to all of you sitting at the table" in standard English can be accomplished quite simply in southern American dialect with the sentence "I want to talk to y'all."
Consequently, the 20 rules of subject verb agreement will vary somewhat by dialect.
1. Subjects and verbs must agree in number. This is the cornerstone rule that forms the background of the concept. In these examples the subject is underlined and the verb is in italics
The dog growls when he is angry. The dogs growl when they are angry.
2. Don't get confused by the words that come between the subject and verb; they do not affect agreement.
The dog, who is chewing on my jeans, is usually very good.
3. Prepositional phrases between the subject and verb usually do not affect agreement.
The colors of the rainbow are beautiful.
4. When sentences start with "there" or "here," the subject will always be placed after the verb, so care needs to be taken to identify it correctly.
There is a problem with the balance sheet. Here are the papers you requested.
5. Subjects don't always come before verbs in questions. Make sure you accurately identify the subject before deciding on the proper verb form to use.
Where are the pieces of this puzzle?
6. If two subjects are joined by "and," they typically require a plural verb form.
The cow and the pig are jumping over the moon.
7. The verb is singular if the two subjects separated by "and" refer to the same person or thing.
Red beans and rice is my mom's favorite dish.
8. If one of the words "each," "every," or "no" comes before the subject, the verb is singular.
No smoking or drinking is allowed. Every man and woman is required to check in.
9. If the subjects are both singular and are connected by the words "or," "nor," "neither/nor," "either/or," and "not only/but also" the verb is singular.
Jessica or Christian is to blame for the accident.
10. The only time when the object of the preposition factors into the decision of plural or singular verb forms is when noun and pronoun subjects like "some," "half," "none," "more," or "all" are followed by a prepositional phrase. In these sentences, the object of the preposition determines the form of the verb.
All of the chicken is gone. All of the chickens are gone.
11. The singular verb form is usually used for units of measurement or time.
Four quarts of oil was required to get the car running.
12. If the subjects are both plural and are connected by the words "or," "nor," "neither/nor," "either/or," and "not only/but also" the verb is plural.
Dogs and cats are both available at the pound.
13. If one subject is singular and one plural and the words are connected by the words "or," "nor," "neither/nor," "either/or," and "not only/but also", you use the verb form of the subject that is nearest the verb.
Either the bears or the lion has escaped from the zoo. Neither the lion nor the bears have escaped from the zoo.
14. Indefinite pronouns typically take singular verbs. *
Everybody wants to be loved.
15. * Except for the pronouns "few," "many," "several," "both," "all," and "some" that always take the plural form.
Few were left alive after the flood.
16. If two infinitives are separated by "and" they take the plural form of the verb.
To walk and to chew gum require great skill.
17. When gerunds are used as the subject of a sentence, they take the singular form of the verb; but, when they are linked by "and," they take the plural form.
Standing in the water was a bad idea. Swimming in the ocean and playing drums are my hobbies.
18. Collective nouns like "herd," "senate," "class," and "crowd," usually take a singular verb form.
The herd is stampeding.
19. Titles of books, movies, novels, etc. are treated as singular and take a singular verb.
The Burbs is a movie starring Tom Hanks.
20. Final Rule - Remember, only the subject affects the verb!
For more examples, check out Examples of Subject Verb Agreement.
The problem with some grammar rules, from the perspective of modern linguistics, is that there is not one absolute grammar rule in the English language. Most American native-English speakers equate standard English with being correct and any non-standard variation of English with being incorrect.
In reality, however, the concept of standard American English is really the privileging of a particular dialect of English that originates from the Ohio River Valley. This is the dialect of English that the anchors of the nightly news speak and that we base our notions of correct and incorrect grammar on. It is important to recognize that no grammar usage is any more correct or incorrect than any other on a functional level, and our notions of correct and incorrect are culturally constructed.