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?

Exercise

Comments

Hello,
could you please clarify two cases regarding usage of 'one/ones' for me:
1. Can we use constructions like 'I wanted to eat one apple but ate two ones instead'
In particular, is it correct to say 'two ones' (with 'ones' acting as a substitute of the noun), or we should just use 'two'?
2. 'I wanted to eat one apple but ate two of them instead'. Can this sentense with 'two of them' be used instead of the prevoius one, or it has a different meaning?

Hello Rhyna,

We would not say 'two ones'. We would most likely say just 'two', but 'two of them' is also possible.

 

Peter

The LearnEnglish Team

Hello Peter,
thanks for a quick reply!
It may be off-topic for this thread, but now I see I made one more systematic mistake in my comment above. Both my questions in there have two parts divided by 'or', and each part is a separate sub-question.
"Can we use... or we should just use". I suppose the second part should also have the reverse word order ('should we use') like in regular questions.
Am I right?
I'm a Russian speaker, and in Russian all questions have the normal word order like in affirmative sentences, so it may be confusing. And when I make such a type of questions, with two individual questions in it separated by 'or', the second part always sounds a bit affirmative to me, as if I was convinced that the answer to it would be positive:)

Hello Rhyna,

Yes, you are right. Both parts should be phrased as questions:

Can I use... or should I use... ?

 

Well done!

 

Peter

The LearnEnglish Team

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,
Kirk
The LearnEnglish Team

hello

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,
Kirk
The LearnEnglish Team

Hello,

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

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