A subject of a sentence is the actor or concept that the sentence is about. A verb is the action of the actor, or the state of being of the concept. Subjects and verbs need to agree in number. A singular subject requires a singular verb, a plural subject requires a plural verb. You need to be able to identify a subject and verb in a sentence in order to see whether or not you have a case of subject-verb disagreement.
Example 1
The following sentences (all taken from the above link) have subject verb agreement errors in them.
One of my friends like to cook Italian food. (Original)
The actor in this sentence is "one of this person's friends". The action they're doing is "liking" cooking Italian food. With this sort of exercise, your verb has to either be the singular "likes" or the plural "like." In this case, a plural verb is the standard form of the verb (like) while the singular verb is the standard form + "s" (likes).
Choosing the correct version means identifying the number of subjects doing the "liking." You have to look for indicator words. We know that one of this person's friends like to cook Italian food, a single subject, and this is indicated by the word "one." That means we have one subject, and the sentence takes the singular verb.
One of my friends likes to cook Italian food. (Corrected)
Example 2
The people who lives next door asked me to get their mail. (Original)
It's easy to identify the subject and verb here. Its important to understand here that whether a word is a countable or non countable noun does not determine whether the subject should be considered plural or singular. People can be both countable and non countable, but here it is a plural subject because the sentence is talking about more than one person.
The people who live next door asked me to get their mail. (Corrected)
Example 3
There is many reasons to disagree about politics. (Original)
In some cases, it can be difficult to identify a subject in the sentence. When you cannot find a subject, look for the verb that is performing an action or expressing a state of being. In this case, the conjugated form of "to be" (is) is the verb. The subject is "reasons" because it is next to it. A verb doesn't always have to come after the subject, sometimes like here it is the other way around. However, a verb should always be connected to the subject or a subject phrase. Reasons are multiple, meaning that they are a plural subject, meaning that "is" should become "are."
There are many reasons to disagree about politics. (Corrected)
Example 4
Leading the club meeting today is Akiko and Jose. (Original)
Identify "who" is leading the club meeting, then identify the verb adjacent. Plural version of "to be" is "are."
Leading the club meeting today are Akiko and Jose. (Corrected)
Example 5
Microsoft, Starbucks and Boeing hires technical graduates from Edmonds Community College. (Original)
Who hires? Microsoft... etc do. There's more than one subject, thus your verb should be plural (standard form).
Microsoft, Starbucks and Boeing hire technical graduates from Edmonds Community College. (Corrected)
Example 6
The number of students in each class vary. (Original)
To determine the subject ("students" or "the number of students in each class") you have to ask who the sentence is about. The subject here is a quantity, it is singular because it is one concept. A singular verb is needed, and as we can see not all singular verbs have a simple "+s" structure
The number of students in each class varies (Corrected)
Example 7
Mathematics prepare students for many different careers. (Original)
The doer of the action (subject) is mathematics, which is "preparing." Mathematics is a branch of knowledge, and a singular subject because the sentence is not talking about different types of mathematics.
Mathematics prepares students for many different careers. (Corrected)
Example 8
Everyone have to take a health class to earn an AA degree. (Original)
Who is doing the action? "Everyone." What is "everyone" doing? They are "having" to take a health class. This is another instance where the subject seems to be plural (everyone is more than one person). However, to determine whether the subject is singular or plural. you have to look at whether the noun being referred to can ever be plural. "Everyone" is a non countable noun, it cannot be plural, and is therefore singular and takes a singular verb.
Everyone has to take a health class to earn an AA degree. (Corrected)
Example 9
Time seem to go quickly during a test. (Original)
You have to look at whether a subject can be written in a plural form in a sentence in order to determine whether its countable in that context. "Time" here cannot be made plural ("times" wouldn't work). Since it is not countable, it is treated as singular and takes a singular verb.
Time seems to go quickly during a test. (Corrected)
Example 10
Neither Sam nor his friends wants to miss graduation
In "either or" and "neither nor" situations the subject is the latter term, in this case the verb "wants" has to be in agreement with "friends."
Neither Sam nor his friends want to miss graduation
click here to see a video breakdown of a few common subject verb agreement errors
Word count: just under 1,000
Questions to answer: what causes subject verb errors to occur and what affects their frequency?
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