Most of the time, determining whether a pronoun should be singular or plural is easy. Just check the noun that acts as the antecedent, and bingo, you’re done. But sometimes a pronoun takes the place of another pronoun. The pronouns being replaced are particularly confusing because they’re singular, even though they look plural.
Here are some problem situations when working with English pronouns:
Everyone, somebody, nothing, and similar pronouns
Everybody, somebody, and no one (not to mention nothing and everyone): These words should be barred from the English language. Why? Because matching these pronouns to other pronouns is a problem. If you match correctly, your choices sound wrong. But if you match incorrectly, you sound right. Sigh. Here’s the deal. All of these pronouns are singular:
The ones: one, everyone, someone, anyone, no one.
The things: everything, something, anything, nothing.
The bodies: everybody, somebody, anybody, nobody.
These pronouns don’t sound singular. Everybody and everyone appear to represent a crowd. Nevertheless, you’re in singular territory with these pronouns. The logic (yes, logic applies, even though English grammar rules don’t always bother with logic) is that everyone talks about the members of a group one by one. You follow this logic, probably unconsciously, when you choose a verb. You don’t say,
Everyone are here. Let the party begin!
You do say,
Everyone is here. Let the party begin!
Picking the correct verb comes naturally, but picking the correct pronoun doesn’t. Check out this pair:
Everyone was asked to bring their bubble gum to the bubble-popping contest.
Everyone was asked to bring his or her bubble gum to the bubble-popping contest.
Which one sounds right? Many people would choose the first one. Unfortunately, the second one is correct, formal English. The bottom line: When you need to refer to ones, things, or bodies in formal English, choose singular pronouns to match (he/she, his/her) and avoid using their.
Each and every in grammar rules
As with everybody, the proper use of each and every sounds wrong. These two pronouns are singular, and any pronouns that refer to each and every must be singular also. Check out these examples:
Each of the motorcycles should have its tires checked.
Every motorcycle with leaky tires will have its inspection sticker removed.
Every car, truck, and motorcycle on the road must display its inspection sticker on the windshield.
Each of the owners must repair his or her motorcycle immediately.
Did you groan? The rule is based on the idea that each and every separate the members of the group into components. Any pronoun referring to each and every is actually referring to a member of the group, not to the group as a whole. Hence, you're in singular territory.
Either and neither grammar wise
Any time you use either and neither alone, these pronouns — and any pronouns referring to them — are always singular. In these sentences, the pronouns that refer to either and neither are italicized:
Either of my daughters is willing to shave her head.
Neither of the drill sergeants wants to deal with his fear of bald women.
Either of the commanders must issue his or her order regulating hair length.
By the way, the last sentence assumes that you have a male and a female commander, or that you don't know whether the commanders are male, female, or a mixed pair.