Whenever you use a personal pronoun like she, they, or it, you first have to have an antecedent, the word the pronoun is replacing.
The pronoun he replaces Gustavo. Pronouns like he will keep you from repeating Gustavo, Gustavo, Gustavo over and over again.
The pronoun must agree with its antecedent. To use this agreement correctly, you will have to know these singular and plural forms:
he, she, it
him, her, it
his, her, hers, its
himself, herself, itself
The general rule for pronoun agreement is straightforward: A single antecedent requires a singular pronoun; a plural antecedent needs a plural pronoun.
In most cases, you will not need to question whether you need a singular or plural form. The spoken English you have heard will help you make the right pronoun choice when you write.
English unfortunately includes some special agreement situations. These will require your more careful attention.
In math, 1 + 1 = 2. This rule applies to pronoun agreement as well. If you have 1 singular noun + 1 singular noun, then together they = 2 things or a plural antecedent.
The plural pronouns their and them are logical and ear-pleasing choices for teacher + assistant and coach + trainer in the two examples.
Two words, however, have incredible sentence power. Each and every are singular and can force an otherwise plural antecedent to become singular as well.
Be careful when you use correlative conjunctions like either…or, neither…nor, and not only…but also. Because conjunctions have two parts, you will find two separate antecedents.
Indefinite pronouns, a special class of words, will often be antecedents. Some indefinite pronouns, despite the illogic, are always singular.
Singular Indefinite Pronouns
each, either, neither
anybody, anyone, anything
everybody, everyone, everything
nobody, no one, nothing
somebody, someone, something
When people talk, logic wins, so you will hear plural pronouns with these words. But when you write, words like everybody, somebody and nothing are singular and require a singular pronoun for agreement.
Because this group of indefinite pronouns is singular, your choice of a singular pronoun might have some people think you are being sexist. If, for example, you say,
then the women present might be offended that you excluded them. Or, if you say,
then the men in the group might wonder why they have to pay.
A solution is to include both genders with constructions like he or she, her or him, his or hers or herself or himself.
While these constructions are grammatically correct, they are also clumsy and can interpret the flow of words in a sentence or paragraph. Another solution is to simply omit the pronoun. Watch:
Another group of indefinite pronouns are singular or plural depending on the information from the prepositional phrase that follows.
Indefinite Pronouns that can be Singular or Plural
all, any, more, most, some
In the first sentence, footwear makes some singular, so it is the pronoun that agrees. In the second sentence, shoes, a plural noun, has all the power. Some becomes plural too, and them is the appropriate pronoun for agreement.
Collective nouns name groups (things) composed of members (usually people). Here are examples:
army, audience, board, cabinet, class
committee, company, congress, corporation, council
department, faculty, family, firm, group
jury, majority, minority, navy
public, school, senate, team, troupe
When the members of the group act in unison (everyone doing essentially the same thing at the same time), then the collective noun is singular and requires singular pronouns for agreement.
When, however, the members of the group act as individuals – each person taking on separate responsibilities or actions – then the collective noun is plural and requires plural pronouns for agreement.
First, substitute a regular plural noun for the collective noun. Then, use a natural-sounding plural pronoun.
A second option is to add the word members after the collective noun. Members is a plural antecedent and requires a plural pronoun.
Many people comprise a business, school or organization. For the purposes of pronoun agreement, however, consider these three groups singular and use it, its or itself to maintain agreement.