Questions about the use of they, them, their, and either themself or themselves to refer to a singular animate antecedent of unspecified gender.
The Oxford English Dictionary gives as the second sense of they the following:
2. Often used in reference to a singular noun made universal by every, any, no, etc., or applicable to one of either sex (= ‘he or she’). See Jespersen Progress in Lang. §24.
Singular they, also known as generic they, has been used in English for at least seven centuries, ever since Middle English when the pronouns were settling down into their modern forms. It is used both in contemporary speech and by many of our finest writers, including Shakespeare, Thackeray, and Jane Austen.
Some prescriptive grammarians, wishing to impose a Latin grammar on English, have objected to this use, but there is no basis for these objects, since Latin grammar never adequately described English in any of its several ages.
In modern times, singular they has increasingly become the natural and preferred way to refer to a human being of unknown or unspecified gender, where using he would be perceived as sexist, using it would be perceived as de-humanizing, and using he or she awkward or intrusive.
Bruce, if you have a significant other, feel free to bring them along.
Generic they is sometimes better thought of as being unspecified not only in gender, but sometimes also in number, as this Shakespeare quote illustrates:
There’s not a man I meet but doth salute me
As if I were their well-acquainted friend.
Like singular you, singular they triggers plural concordance in its verb:
I don’t who’s here, but they aren’t getting in the door.
The reflexive form themself is used like the reflexive form of singular you:
- Mary, if you want a dish you can make for yourself, let me know.
- Anyone who wants a dish they can make for themself should let me know.