Interrogative Adjectives: Which, What and Whose

An interrogative adjective asks a question about the noun it sits in front of. There are three: which, what, and whose.

• Which platform leaves first?
• What colour did you choose?
• Whose coat is on the chair?

Remove the noun and they stop being adjectives. Which leaves first? uses which as a pronoun, because it no longer modifies anything – it stands in for the platform itself. That is the whole distinction, and it is worth knowing only because grammar exercises test it constantly.

Which or what?

Both ask you to pick, but they imply different sized fields.

Ask which size when a shop stocks small, medium and large. Ask what size when you have no idea what sizes exist. Native speakers apply this without thinking, and getting it wrong rarely causes confusion – but which in front of an open field sounds oddly restrictive, as though the answer must come from a list the listener cannot see.

Whose, and the apostrophe trap

Whose is the possessive interrogative adjective. Who’s is a contraction of who is or who has. They sound identical and mean nothing alike.

• Correct: Whose turn is it? – asking about ownership
• Correct: Who’s next? – asking who is
• Test: read it as who is. If the sentence survives, you need who’s.

This is the same pattern as its and it’s, and it catches people for the same reason: the apostrophe marks a missing letter, not possession, which feels backwards given that every other possessive uses one.

In indirect questions

Interrogative adjectives survive when a question is folded into a statement, and the word order changes with them.

• Direct: Which train should I take?
• Indirect: She asked which train she should take. – not which train should she take

The inversion that marks a question disappears once the question is reported. Keeping it is one of the most common errors among learners, and one of the easiest to hear once you know to listen for it.

What they are not

Whose, which and what also introduce relative clauses, where they are doing a different job entirely – the coat whose lining is torn makes no question at all. For that use, see adjective clauses.

Practice

Fill the gap with which, what or whose. Answers below.

1. ___ of these three keys opens the side door?
2. ___ bag has been left in the corridor?
3. ___ time does the last train leave?
4. She asked ___ file I had opened.
5. ___ going to lock up tonight?

Answers

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