Every student aced his project.
Many professors make every student buy their own books.
Everyone will be able to decide for himself whether or not to have an abortion.Can "they" be singular?
We're certainly trying hard to make it so. This is done so as not to offend women by using "he" to stand for either gender, which is what I learned in school umpteen years ago.
Those of us who don't like "they" being singular try "he or she," or we write around it: All the students aced their projects.
No one is really happy with their solution.
On The Economist's Johnson blog, the estimable Robert Lane Greene throws everything he has into the argument that a singular "they" is okay. Including the fact that Chaucer, Shakespeare, the King James translators, Swift, Byron, Austen, Goldsmith, Thackeray, Shaw, Herbert Spencer and others used it that way.
I wouldn't be caught dead in that crowd.
When I wrote for The Associated Press back in the olden days the title "Ms." came into being. Cautious about changing its style rules, The AP instructed us to say "Ms. Woman, who prefers that designation." That is just so awkward that I did anything to avoid it. I preferred to not quote a woman than add that silliness to my poetry.
So I'm going to stick with "they" as a plural, because the alternative just grates on my ear. That's my reason, and I won't hear of anything different.