Making sure that the subject and verb agree in a sentence is important. When they agree correctly they will make the essay or report easier to read and understand. There are a few techniques that will need to be taken to ensure the subject and verb are in agreement.The verb in every independent or dependent clause must agree with its subject in person or number.
The two numbers are:
- singular- indicating one person or thing
- plural- indicating more than one person or thing
For the subject and verb to agree in singular or plural subjects, they must have a singular or plural verb. The subject takes the base form of the verb in all but the third person singular to make the subject and verb agree in person. The subject and verb must comply in number. In third person singular add an s or es to the base form of the verb to make both the subject and verb agree.
Example: The dog jumps the fence.
- The subject is: dog
- The verb is: jumps
Example: The dogs jump the fence.
- The subject is: dogs
- The verb is: jump
Eugenia Butler states in her book Correct Writing, "Compound subjects joined by "and" normally require a plural verb." The only instance when this is not applicable and the subjects are considered singular is when the subjects refer to the same individual or object.
Remember: "Nouns joined by "and" are thought of as a unit or actually refer to the same person or thing, the verb is normally singular".
Example: My friend Jenn and colleague Sarah are going on vacation.
Example: The restaurant owner and head chef is coming to the party. (referring to the same person, singular)
When compound subjects joined by “or” or “nor”, the verb follows the nearest subject.
Example: My brother or sister is throwing me a party. (nearest subject, sister, is singular)
Example: Neither my boss or co-workers are feeling well today. (nearest subject, co-workers, is plural)
Verb Preceding the Subject
Verbs sometimes come before the subject. This change in order can lead to error in agreement. It is sometimes difficult to remember when the verb comes before the subject. Below you will find some guidelines and examples to help you.
In normal everyday English, verbs precede the subject.
To make questions "Does he?" "Can you?"
After 'so' 'neither', 'nor' "So do I", "Neither do I", "Nor do I"
In written English, as well as in a very formal style, the verb precedes the subject is in the following cases:
After negative adverbial expressions
- Under no circumstances can we accept cheques.
- In no way can he be held responsible.
- At no time did she say'' she would come.
After adverbial expressions of place :
- Round the corner came the postman.
- On the doorstep was a bunch of flowers.
After 'seldom', 'rarely', 'never', in comparisons :
- Seldom have I seen such a beautiful view.
- Rarely did he pay anyone a compliment.
- Never had I felt so happy.
After 'hardly', 'scarcely', 'no sooner', when one thing happens after another. :
- Hardly had I begun to speak when I was interrupted.
- Scarcely had we started our meal our meal when the phone rang.
- No sooner had I arrived than they all started to argue.
After adverbial expressions beginning with 'only' :
- Only after the meeting did I realize the importance of the subject.
After exclamations with 'here' and 'there' :
- Here comes the winner!
- There goes all our money!
An intervening expression is an expression that describes the subject and should not affect the verb. These expressions are often mistaken for being the subject of the sentence. Verbs are sometimes separated by words that describe the subject. This can make it difficult to make sure that the subject and verb agree. The key is to make sure that the verb agrees with the subject and not with the word in the modifying phrase. With intervening words ending in "s", such as sometimes and always, the "s" ending still must appear on a present tense verb if the subject is singular.
Example: The evidence that they submitted to the judge was convincing.
- The subject is: evidence
- The verb is: was
The singularity of a subject is not changed by the introduction of phrases or clauses that appear to change the number of the subject.
Sentence structure and formation are key elements of the English language, certain rules exist that when applied correctly give the writer a powerful tool of communication. 
In her work Grammar: A friendly Approach, author Christine Sinclair, reminds the reader of the dangers of intervening expressions and phrases, and how they can make the reader forget "who" or "what" the sentence is about. 
Example: Exercise, along with proper rest, is vitally important.
- The subject is: exercise
- The Verb is: is
When intervening words ending in "s", such as sometimes and always, the "s" ending must be present on a present tense verb if the subject is singular.
Example: Her driver always makes wrong turns.
Other Common expressions that sometimes appear to change the number of the subject and verb include but are not limited to :
- In addition to
- As well as
- Together with
The author Jarvie Gordon, describes common grammatical errors of English language sentence formation in the work Bloomsbury Grammar Guide, by providing examples of common subject/verb agreement sentences and how the reader can recognize the number of the subject and verb when an intervening expression or phrase is introduced into the sentence. 
Verb Agreement with Indefinite Pronouns
Some pronouns are definite in the fact that they can replace a specific noun or another pronoun. But sometimes things aren’t so clear-cut. So what do we do for a pronoun when we find ourselves in this predicament? We will use indefinite pronouns. "Indefinite pronouns refer to nonspecific persons or things." Some of these indefinite pronouns are always singular or always plural. But some can change their number—they can be either singular or plural, depending on the context. There are two categories of indefinite pronouns. The first category includes pronouns that refer to a nonspecific noun. These pronouns are: anything,somebody, no one, and something. An example sentence using the first category of indefinite pronouns is:
- Somebody is at the door.
The second category of indefinite pronouns are those that point to a specific noun whose meaning is easily understood only because it was previously mentioned or because the words that follow the indefinite pronoun make it clear. These pronouns are: both, all, few, and either. An example sentence using the second category of indefinite pronouns is:
- Both do well at taking tests.
- Kirszner, Laurie G., and Stephen R. Mandell., The Concise Wadsworth Handbook. Instructor's Ed. Australia: Thomson/Wadsworth, 2005, p.240. 
- Butler, Eugenia, et al., Correct Writing. 6th Ed. Lexington: D.C. Hath and Company, 1995, p.143-145. 
- Rothstein, Evelyn, and Andrew Rothstein. English Grammar Instruction That Works! : Developing Language Skills For All Learners. Thousand Oaks, Calif: Corwin Press, 2009. eBook Collection (EBSCOhost). Web. 25 Apr. 2014
- Sinclair, Christine. Grammar : A Friendly Approach. Berkshire, England: McGraw-Hill, 2010. eBook Collection (EBSCOhost). Web. 24 Apr. 2014
- Jarvie, Gordon. Bloomsbury Grammar Guide. London: A. & C. Black, 2007. eBook Collection (EBSCOhost). Web. 25 Apr. 2014.
- Hacker, Diana. A Writer's Reference. New York, Boston: Bedford/St.Martin’s, 2003.