The basic subject-verb agreement rule in English is very simple. It states that a singular subject takes a singular verb, while a plural subject takes a plural verb. However, there are a few problems with this formulation of the rule that need to be mentioned.
To begin with, the rule makes it sound as if each and every verb has one singular form that is used with all singular subjects and one plural form that is used with all plural subjects. This is not true. If we disregard the verb be and the modal auxiliaries, all verbs have one form that is used in the third person singular, that is, with the pronouns he, she, and it, and with subjects that could be replaced by one of these three pronouns, as in example (1) below, and one form that is used with all other subjects, i.e. first and second person singular subjects (2) and all types of plural subjects (3):
(1) My sister has a baby.
(2) I have a headache and you have one too.
(3) They know her well.
The rule also makes it sound as if plural agreement is of importance in all tenses. This is not true either. Except for the case of the verb be, subject-verb agreement only takes place in the present tense. So, what we really need to remember, if we simplify the situation somewhat, is to put an -s on the verb in the third person singular (and to use the correct forms of be, have, do, and verbs like try and deny, which become tries and denies in the third person singular).
However, one problem remains. How do we know in each and every case whether the subject is (third person) singular or plural? In most cases, this is not a problem, since if the subject is a single person, animal, or thing, we have singular agreement, and if the subject is more than one person, animal, or thing, we have plural agreement.
In other words, as pointed out above, if he, she, or it could be used instead of the subject, we have (third person) singular agreement, but if we could use they instead of the subject, we have plural agreement. This is what is illustrated in the box below.
In the examples in the box, as well as in the examples used to illustrate the rules below, the relevant subjects appear within square brackets, while the heads of the relevant subject noun phrases and the first verb (i.e. the agreeing verb) of the verb phrase appear in boldface.
[She/He/it] talks. = Singular subject and singular verb
The pronouns she, he, and it are examples of third person singular subjects, and the -s on talks indicates that talks is a third person singular verb.
[They] talk. = Plural subject and plural verb
No -s on the verb, since the subject they is plural.
[The kid] talks. = Singular subject and singular verb
The subject the kid is third person singular, since the head of the noun phrase functioning as the subject is the third person singular noun kid. Therefore we use the third person singular verb form talks.
[The teachers] talk. = Plural subject and plural verb
No -s on the verb, since the head of the noun phrase functioning as the subject is the plural noun teachers.
However, there are several cases where the facts are more complicated than this. Otherwise, subject-verb agreement would not be such a big issue for people writing in English. Some of the more important of those more complicated cases will now be listed and exemplified, and, in some cases, briefly discussed.
Before we turn to this discussion it must be stated very clearly that when we say that the subject and the verb must agree with each other, we mean - in the case of noun phrase subjects - that the head word of the noun phrase must agree with the first verb of the verb phrase.
Various cases of subject-verb agreement in English are discussed in the following subsections:
- Singular noun phrases connected by "or"
- Singular noun phrases connected by "either/or"
- Connected singular and plural noun phrases
- Noun phrases conjoined by "and"
- Subjects containing "along with", "as well as", and "besides"
- Indefinite pronouns and agreement
- Sums of money and periods of time
- Words that indicate portions
- Uncountable nouns
- Dependent clauses and agreement
- Agreement with the right noun phrase
- Some important exceptions and words of advice