One / Ones as Substitute Pronouns
Level A2 · Pronouns & Possessives
one and ones can replace a noun already mentioned, so you don't have to repeat it — especially after an adjective that distinguishes which one you mean. I like the red shirt, not the blue one replaces shirt with one after blue, avoiding I like the red shirt, not the blue shirt. ones does the same job for plural nouns: These shoes are too small; I need bigger ones.
How one and ones work as substitutes:
- one replaces a singular countable noun already mentioned, usually after an adjective or determiner: I don't want this pen, I want that one; Do you have a bigger size? I need a smaller one.
- ones replaces a plural countable noun already mentioned, in the same way: These apples are sour; the green ones are sweeter; I don't like small cars — I prefer big ones.
- one/ones is optional (though common) after this/that/these/those alone, but required after most adjectives when the noun is dropped: this one is fine (this alone also works); but the red one needs one — not just the red.
- one/ones cannot replace an uncountable noun — you can't say I'd like some water, not that one; with uncountable nouns, simply repeat the noun or drop it: I'd like some water, not that (bottled water).
The most common mistake is dropping one/ones after an adjective when the noun has already been removed, leaving the adjective stranded — I like the red, not the blue is incomplete in standard English; add one: I like the red one, not the blue one. A second mistake is using one/ones with uncountable nouns — I'd like some coffee, not that one is wrong for uncountable coffee; say I'd like some coffee, not that (or repeat coffee).
Look for an adjective or determiner standing alone right before a gap where a noun was just mentioned — if the noun is countable and singular, add one; if plural, add ones. If the earlier noun is uncountable, don't add one/ones at all.