Subject
they
Object
them
Possessive
their
Possessive (alone)
theirs
Reflexive
themselves
Said like: thay / them / thair / thairz / them-SELVZ
They is the pronoun most non-binary people use, and the one most people already know how to say. You use it every day for someone whose gender you don't know: "someone left their umbrella, I hope they come back for it." Using it for a named person you are looking at is the same word doing a slightly newer job.
The grammar does not change. They still takes the plural verb, the way you still says "you are" for one person. The only real choice is the reflexive: themselves is standard, themself is common and getting commoner. Both are understood. Neither is wrong.
In a sentence
They said they would meet you at seven, so text them if the train is late.
That is their coat on the chair, and the umbrella is theirs too.
They built the shelf themselves and are quietly proud of it.
How to use them
- Verb agreement stays plural: "they are", "they have", "they were". Saying "they is" sounds wrong to everyone, including the person you are talking about. Think of you, which has worked this way for centuries.
- Themself or themselves: both are used for one person. Themselves is the safer choice in formal writing; themself is common in speech and increasingly in print. Pick one and stop worrying about it.
- If a sentence is ambiguous, use the name. "Sam and Jo went out and they lost their keys" is unclear whoever the pronoun refers to. That is a sentence problem, not a pronoun problem, and the fix is the same as it always was.
- When you slip, correct and move on in the same breath: "she said, sorry, they said, that they'd be late." No apology speech. A long apology makes the other person comfort you, which is the opposite of the point.
- To ask, ask plainly and offer your own first: "I use he, what do you use?" It is a two-second question. Do not ask in front of an audience if you can avoid it.
Ways to practise
- Write three sentences about the person in your head, using they, their and theirs. Then say them out loud. The mouth learns faster than the eyes.
- Narrate someone you don't know for a minute: the person across the café, the cyclist at the lights. "They're checking their phone. That coffee is theirs." It is the same grammar you have used all your life.
- Practise the correction, not just the pronoun. Say the wrong one on purpose, fix it in three words, carry on. The recovery is the skill people notice.
Where it came from
Nobody coined it. Singular they was already in use by the 14th century, about a century after plural they arrived from Old Norse, and the reflexive themself is attested from the 14th to the 16th century and has been increasing again since the 1970s. The non-binary use is the recent part: dictionaries have added it within the last decade.
Who uses them
Identities whose pages mention this set. A pronoun never tells you what someone is — this is only where the word turns up.
Questions people ask
Isn't they plural?
It is both, and has been since the 1300s. You is plural too, and nobody objects to "you are" for one person. The word does two jobs and English speakers handle the ambiguity without noticing, the way you just did with "someone forgot their bag".
Which is right, themself or themselves?
Both are in use for a single person. Themselves is the standard form; themself is older than it looks, attested from the 14th century, and has been growing again since the 1970s. Use whichever the person uses for themself, and if you don't know, either is fine.