Ellipsis and Substitution: Leaving Out and Replacing Words

English speakers dislike unnecessary repetition. Compare: Do you want a coffee? Yes, I want a coffee, with the natural Yes, please or Yes, I do. Both are correct, but the first sounds robotic.

There are two main tools. Substitution replaces a word or phrase with a short substitute word: one, do, so, not. Ellipsis leaves the words out completely, because the listener can understand them from the context. Both make speech faster and writing more cohesive, because they connect each sentence to what came before.

The golden rule: you can only leave out or replace something that the listener can recover easily from the previous sentence or the situation.

Use one to replace a singular countable noun and ones for a plural: this one, the big one, the ones on the left, a new one. One often comes after an adjective or after this, that, which and the.

Do not use one directly after a possessive: say mine, not my one, in formal English (with an adjective it is fine: my old one); my one is common only in informal British speech. Do not use one for uncountable nouns: I like hot milk, but not cold (not cold one). After a number or a word like each, several or both, we usually leave one out unless there is an adjective: I bought three, but I bought three cheap ones. After a superlative, one is optional: Take the cheapest (one).

The most common ellipsis in English keeps the auxiliary verb and drops the rest: I haven't seen it, but Ana has. If the first clause has no auxiliary, use do, does or did: She likes jazz and I do too. This is the same system as short answers and question tags.

To agree with someone, use So + auxiliary + subject for positives and Neither or Nor + auxiliary + subject for negatives: I'm hungry. So am I. I didn't sleep well. Neither did I. Notice the inversion. Informally you will also hear Me too and Me neither.

In British English, do can follow a modal or perfect auxiliary: Will you call him? I might do. Have you finished? I have done. American English prefers I might and I have.

So replaces a positive that-clause after verbs of thinking and speaking: think, hope, expect, suppose, believe, guess, be afraid, say, tell. Is it true? I believe so. Who says so? Not replaces a negative clause: Is it serious? I hope not.

Do so replaces a verb phrase in formal writing: The company promised to reduce prices but has not yet done so. In everyday speech, people prefer do it or do that: I wanted to call her but I didn't do it.

You may also see if so and if not in instructions and emails: Are you over 18? If so, sign below. If not, ask a parent.

After verbs like want, need, like, love, hope, try, have and ought, we can keep to and drop the verb: Would you like to join us? I'd love to. You don't have to if you don't want to. This is very natural in speech; do not drop to as well (I'd love is wrong).

In linked clauses with and, but and or, repeated subjects and auxiliaries are normally left out: She opened the door and (she) walked in. I've washed the dishes and (I've) cleaned the floor. Repeated nouns can also go: Some students passed and some (students) failed.

After wh-words, a whole clause can be dropped: Someone has taken my bag, but I don't know who. We need to leave early. Why?

In casual speech, people often drop words at the start of a sentence, especially pronouns, auxiliaries and articles, when the situation makes them obvious: (Do you) Want a drink? (It) Sounds good. (Have you) Seen Ana? (I'm) Not sure. (There's) Nothing to worry about.

This is called situational ellipsis. It is normal in speech, text messages and informal emails, but avoid it in formal writing. In formal texts, use substitution and textual ellipsis instead: they make writing concise without sounding casual. For more on spoken English, see how to improve your English speaking and small talk in English.