Grammar is a strict matchmaker: singular subjects must be paired with singular verbs, and plural subjects can associate only with plural verbs. Each must stick with its own kind. But they frequently intermingle, forming combinations that are unnatural in the United States.
Some examples are obvious: “The company says they will meet their profit targets in 2010.” “Company” is a singular noun, but “they” and “their” are plural pronouns. That sentence would be (almost) correct in places that follow British English—where “company” is construed as a plural collective noun—but not in the United States. (“Almost” correct: the British would say “The company say they will meet their profit targets in 2010.”)
Collective nouns—words that describe a group, like “tribe,” “team,” “nation,” etc.—are usually singular in U.S. English, taking the singular pronoun “it.” In many cases, though, you can use plurals with collective nouns in contexts where the individual is highlighted instead of the group, like “faculty,” “clergy,” and “people,” as long as you stay consistent. But mixing an obvious single with an obvious plural is grammatical adultery.
Here’s one example where the pronouns swing both ways: “The crew of a cargo aircraft that traveled from North Korea and was detained in Thailand said it did not know they had been transporting an arsenal.” The singular “crew” is latched on to both singular and plural pronouns. In this case, “it” would have been preferred, though you can also change “crew” to “crew members” and use “they” without risking derision.
But throw in a little sex, and chaos ensues.
Let’s take the sentence “Everyone should have their taxes filed by April 15.” “Everyone” is a collective noun meaning “each person.” “Person” is obviously singular. But if you said “Everyone should file his taxes by April 15,” the feminists will be on you faster than the IRS. Use “her taxes,” and traditionalists will accuse you of being too politically correct.
English has no sex-neutral personal pronouns. So people twist themselves into knots to avoid appearing sexist. (“People” is used here as a plural collective, followed by its plural kinfolk.) Sometimes writers alternate, using “his” in one place and “hers” in the next. But the poor reader has to alternate between thinking of the subject as “him” and “her.”
The frequent default is to play it straight down the middle: “Everyone should have his or her taxes filed by April 15.” But that’s just clumsy, and can easily be contorted into the kinds of phrases often found in academia: “Each child’s parent should be told that his or her child will be challenged to live up to his or her potential.”
Far simpler would be to work around the problem. “Everyone should file taxes by April 15”; “Every parent should be told that each child will be challenged to reach the fullest potential.”
You can wriggle out of such a bad date in any number of ways. One is to remove the sex completely: “After each judge has received the decision from his clerk, the court reconvenes” can become “After each judge’s clerk has delivered the decision …” You can rework a sentence to replace “him” or “her” with the relative pronoun “who”: “If a politician can’t get health care right, he’s not worth the vote” can became “A politician who can’t get health care right isn’t worth the vote.” You can transition the pronoun into an article, changing “Does everyone have his/her/their ticket?” to “Does everyone have a ticket?”
Whatever you do, make sure you practice safe pronoun use.