“Can We Take “They” as a Singular Pronoun?” by Ben Zimmer. The Wall Street Journal, 4/11/2015.
Anyone who writes even a little has struggled with the politically correct phrase, “he or she.” For example, the sentence
When a person becomes a top executive, he or she often misses the comradery of his or her former co-workers.
is politically and grammatically correct, but sure is awkward. Writing it
When a person becomes a top executive, they often miss the comradery of their former co-workers.
is simpler and understood by everyone, but would never be allowed by grammarians because we are changing tense. We are starting out singular and finishing plural. That is always a basic error. Yet we are seeing more of this, and I prefer it myself. No one yet has complained of misunderstanding.
The problem is because English does not have the needed gender-neutral singular third-person pronoun. Just a generation ago, we would have happily used “he” in the above example, implying all top executives (and doctors, and politicians, and high-achievers in general) are men. That doesn’t fly today.
Using “they” and “their” as singular, gender-neuter pronouns just makes sense, is much easier than inventing new words, and is already used in daily speech, although it is more precise to say the plural “they” can refer to a gender-neutral singular subject (note the plural verb “miss,” rather than the singular “misses” is still used with “they”).
Grammarians are now discussing the problem, but it is not their choice to make. Grammar defines usage, not dictates it. People will speak and write however they want, and it is for the grammar rules to keep up. If this was simple, the problem would have been solved long ago.