We use one (singular) and ones (plural) to avoid unnecessary repetition.

See those two girls? Helen is the tall one and Jane is the short one.
Which is your car, the red one or the blue one?
My trousers are torn. I need some new ones.
See those two girls? Helen is the one on the left.
Let’s look at the photographs. The ones you took in Paris.

We often use them after Which ... in questions:

You can borrow a book. Which one do you want?
There are lots of books here. Which ones are yours?



Hello ! I have a question about the first sentence: Is it wrong if I say :
The younger is four and the older is seven (without ''one'').
Thank you in advance .

Hello Abfalter Cristian,

In English, adjectives are not used to substitute nouns in the way they are in some other languages. I don't know Romanian, but in Spanish, for example, using an adjective in this way is common.

So in the first sentence, the best thing is to use 'one' in both gaps. You might be able to find examples where this rule is not followed, but in general I would not recommend it.

All the best,
The LearnEnglish Team


Could I use Which for people as well? As: Did you see the girl over there? Which one? The one with a pony or with short hair?

thanks in advance.

Hello pencil,

Yes, that is correct and perfectly natural.

All the best,
The LearnEnglish Team


Does this topic comes under "Indefinite Pronouns" or it is different?

Hello Peter,

Thank you for the clarification.

If possible can you envelop all the indefinite pronouns together to avoid future confusion?. Also, it will help to avoid pupil to refer different websites for one subject.

Hello Lijo John,

Thank you for the suggestion. We'll make a note of it for the next time we review the site organisation.



The LearnEnglish Team

In the following examples: (used in the rule of one / ones)
1- See those two girls? Helen is the tall one and Jane is the short one.
2- See those two girls. Helen is the one on the left.
My question is, why did you use a question mark after the first clause in the first example while you did not use it in the second?

Hello FirasAkkad,

That was a mistake! It should end in a question mark and I've now fixed it.

Thanks very much for taking the time to point this out to us.

All the best,
The LearnEnglish Team