Agreement (Pronoun / Antecedent)

You may be surprised to find that the following sentence, after decades of being considered nonstandard, is now considered standard in standard edited English. 

Standard
Every semester, a student leaves the class without their umbrella.

Here, the new third-person singular pronoun “their” refers back to the singular word “student.”

This used to be considered an agreement error, but both the Chicago Manual of Style and the American Psychological Association have changed their standards.

Other standard ways of expressing the idea in the sample sentence above include substituting “his or her” for “their” or by making the word it refers to plural so that it agrees with the plural pronoun. The Chicago Manual of Style prefers these uses in formal writing:

Standard (Formal)
Every semester, a student leaves the class without his or her umbrella.

Standard (Formal)
Every semester, students leave the class without their umbrellas.

The subjective case pronoun they can also be used with a singular antecedent:

Standard
If someone wants to join the club, they need to bring a check for five dollars.

In the sentence above, the singular indefinite pronoun someone is paired with the singular subjective case pronoun they. If necessary, this can be re-written in a number of ways, some more awkward than others:

Standard (Formal)
If someone wants to join the club, he or she needs to bring a check for five dollars.

Standard (Formal)
If someone wants to join the club, that person needs to bring a check for five dollars.

Standard (Informal)
If you want to join the club, you need to bring a check for five dollars.

Standard (Informal)
If people want to join the club, they need to bring a check for five dollars.

All of the above are correct, but the first two are more formal and the last two are more informal. Consider your audience as you consider your use of pronoun / antecedent agreement.

When dealing with animals, abstractions, or inanimate objects, be careful to use plural pronouns with plural antecedents and singular pronouns with singular antecedents.

Nonstandard
When a parrot is given a command, you can often expect a reasonable response from them.

Here, the singular word “parrot” needs a singular pronoun.

Standard
When a parrot is given a command, you can often expect a reasonable response from it.

Here are some examples that deal with abstractions or inanimate objects.

Nonstandard
The issues that relate to lying, cheating, and stealing are serious, and it must be addressed immediately.

Standard
The issues that relate to lying, cheating, and stealing are serious, and they must be addressed immediately.

The agreement is between the plural noun “issues” and the plural pronoun “they.”

Nonstandard
Every motorcycle I’ve ever ridden, no matter what time of year or time of day, has had their engine break down in the middle of the ride.

Standard
Every motorcycle I’ve ever ridden, no matter what time of year or time of day, has had its engine break down in the middle of the ride.

The agreement is between the singular noun “motorcycle” and the singular possessive pronoun “its.”

Here are some other examples of standard use of the new third-person singular pronouns:

Standard

Everyone oversleeps at least once in their lifetime.

A doctor must have their medical bag with them at all times.

Every time a librarian says I have an overdue book, I can’t look them in the eye for weeks afterward.

The person at the entrance will scan your ticket with their device.