One is a substitute word. We often use one instead of repeating a singular countable noun.
- ‘Which is your boy?’ ‘The one in the blue shirt.’
- I want that one, not this one.
- ‘Can you lend me a pen?’ ‘Sorry, I haven’t got one.’
One has a plural ones.
- Green apples often taste better than red ones.
Leaving out one(s)
One(s) can be left out immediately after superlatives, this, that, these, those, either, neither, another and some other determiners.
- I think my dog is the fastest (one).
- Either (one) will suit me.
- Let us have another (one).
- ‘Which (one) would you like?’ ‘That looks the nicest.’
We do not use one(s) immediately after my, your etc., some, any, both or a number.
- Take your coat and pass me mine. (NOT … my one.)
- I need some matches. Have you got any? (NOT … any ones?)
- Are there any grapes? Yes I bought some today. (NOT … some ones today.)
But note that one(s) is used in all these cases if there is an adjective.
- Are there any mangoes? Yes, I bought some sweet ones today.
- Has the cat had her kittens? Yes, she had four white ones. (NOT … four white.)
We do not use one(s) for uncountable and abstract nouns.
- If you haven’t got fresh cream I will take tinned (cream). (NOT … tinned one.)
- The Dutch grammatical system is very similar to the English system. (NOT … the English one.)
One and It
To refer to one particular thing that has already been clearly identified, we use it, not one.
- ‘Could you lend me a bicycle?’ ‘Sorry, I haven’t got one.’
- ‘Could you lend me your bicycle?’ ‘Sorry, I need it.’
One (indefinite personal pronoun)
We can use one or you to talk about people in general.
- One/you should not do such an unkind thing as that.
- One/you should love one’s/your country.
Note that one is more formal than you.
One is not used to generalise about people who could not include the speaker; you is not used to generalise about people who could not include the hearer.
- One/you must believe in something.
- In the sixteenth century people believed in witches. (NOT … one/you believed in witches – this could not include the speaker or hearer.)
Pronouns referring back to one
When one is used in American English, he, him and his are generally used later in a sentence to refer back to one. This is not normal in British English.
- One should love his country. (US)
- One should love one’s country. (GB)
One can be a subject or object; there is a possessive one’s and a reflexive pronoun oneself.