Relative Clauses with ที่ / ซึ่ง

One word for who, which and that

English picks a relative pronoun depending on what it refers to: the man who, the book which, the shop that. Thai uses thii (ที่) for all of them. It goes straight after the noun it describes, and the describing clause follows: khon thii yu thii nan, the person who lives there. ran thii pit laeo, the shop that has closed. Because Thai already puts describing words after the noun, this feels like a natural extension of adjective order rather than a new structure.

The other jobs of thii

thii also means 'at' or 'place': yu thii ban, at home. And thii nii, thii nan, thii nai are here, there and where. It is a classifier too, for portions of food: song thii, two portions. And it forms ordinals: thii nueng, first; thii song, second. One syllable, five jobs. In practice the position in the sentence makes it obvious which one is meant, but it is worth knowing the list so a familiar word in an unfamiliar place does not stop you.

Describing which one you mean

This is the everyday use: narrowing down which thing you are talking about. It is how you point at something in a shop without knowing its name. an thii sii daeng: the red one. an thii yu khang lang: the one at the back. khon thii sai suea sii khiao: the person in the green shirt. Combine it with a classifier and you can identify anything in sight, which is more useful for a beginner than any amount of vocabulary.

sueng, and when to use it

sueng (ซึ่ง) is the formal relative pronoun. It appears in writing, in news, in official notices and in speeches, and almost never in conversation. It is used for non-restrictive clauses - the kind English sets off with commas: the temple, which was built in 1782, is nearby. As a learner you need to recognise it when reading and you can safely never produce it. thii covers everything you will say out loud.

Pointing things out

Almost everything a beginner needs to say about which thing they mean is in here.

Choosing between who and which

There is nothing to choose. thii covers people, things, places and ideas alike. Learners who studied European languages sometimes hunt for a second form for people; there is not one. The only variation worth knowing is the formal sueng, and that is a register choice rather than a grammatical one.

Dropping thii where it is needed

Two nouns next to each other can be a possessive (ran phuean, a friend's shop). If you leave out thii from a relative clause, that is what a listener hears first. When a whole clause with a verb in it describes your noun, put thii in. Where the description is one plain adjective, leave it out: ran yai, a big shop, needs no thii.