- If someone from the insurance company calls, tell them that they can come and see me tomorrow.
- If a teacher only ever read from the textbooks, their lessons wouldn’t be very interesting.
- I never refuse to mark a student’s work just because they don’t give it in on time.
Here, they, them and their are clearly third person singular. Why?
In these examples, neither he/him/his nor she/her/her is possible because we do not know the sex of the person referred to – it could be either a man or a woman. When this is the case, they/them/their is frequently used as a “neutral” singular pronoun. The following verb, however, remains grammatically plural : RIGHT - they don’t give it in WRONG - they doesn’t give it in.
Sometimes the problem can be avoided by putting the noun referred to in the plural, at which point they is used normally : I never refuse to mark students' work just because they don't give it in on time. But when the noun is someone or anyone, this is not an option. The only alternative is to use he or she (often abbreviated to s/he), his or her etc and this can often sound clumsy - If someone from the insurance company calls, tell him or her that he or she can come and see me tomorrow.
This use comes up frequently in the instructions to pairwork activities - Ask your partner if they have ever ridden a camel. Ask your partner about their childhood - and can be pointed out when it occurs. Students can then be given an activity where they have to choose an appropriate reference word to complete a sentence :
- Janet left you a message but I don't know where they/she/he put it.
- I've no idea who left the message. I didn't see her/him /them.
- David has lost his/her/their keys again.
- Look! Somebody has lost her/his/their keys.
- We need to advertise for a new Marketing Manager. He /She/ They will have to be available immediately.
- The new Marketing Manager arrived yesterday. His /Her /Their name is Annette.
Instead of giving the options, the exercise could be made slightly more difficult by simply leaving a blank for the students to complete.
For a good discussion of the historical use of singular they – including its use by writers such as Shakespeare and Jane Austen - see the Wikipedia.