their vs there

The core difference

These two are homophones with nothing else in common. Their is a possessive determiner, the plural of his and her. It always sits in front of a noun and tells you who owns it. There is an adverb of place, and also the dummy subject that English uses to announce that something exists.

Using each one

• Their + noun: Their flight was cancelled. The students handed in their essays.
• There = a place: Put the boxes down there. We drove there in an hour.
• There = existence: There are three messages waiting. There's no milk left.

Two tests you can run

For 'their': swap in 'our'. If the sentence still works — 'our car broke down' — you want their. Both are possessives, so they slot into the same place.

For 'there': look for 'here' inside it. The word there literally contains here, and both are about location. If you could swap in here, or if the sentence starts 'There is / There are / There was', you want there.

The third one people forget

They're is the contraction of they are: 'They're late again.' If you can expand it to 'they are' without the sentence collapsing, use they're. All three sound the same in ordinary speech, so the apostrophe check is worth running whenever you write any of them.

Common mistakes

The classic slip is there before a noun: 'there house', 'there parents'. A determiner slot before a noun almost always wants their.

The other is their's, which does not exist. Possessive pronouns take no apostrophe: theirs, like hers, ours and yours. 'The blue one is theirs.'

Worth knowing: singular their — 'someone left their coat' — is entirely standard English and has been used by respected writers for centuries. It is not a modern error, whatever you may have been told at school.