Ellipsis and substitution in English: I think so, neither do I, and the words you are allowed to leave out

Ask a learner Do you like coffee? and you often get Yes, I like coffee back. Every word of it is correct, and no native speaker has ever said it. The real answer is Yes, I do, or just I do, or a nod and mm. Natural English is full of holes. Words that the listener can work out for themselves get left out, and a handful of small words - so, not, one, do, too, neither - stand in for whole phrases.

Grammar books call the leaving-out ellipsis and the standing-in substitution, and then say very little else about either, which is odd, because between them they are most of what makes speech sound like speech. A learner who answers in full sentences is not making mistakes. They are answering exam questions out loud. This page is about how to stop.

The engine: the auxiliary stays, the rest can go

English lets you delete a repeated verb phrase as long as you keep the auxiliary in front of where it was. The auxiliary is the receipt: it proves the missing words were there.

• She can sing and he can sing too. → She can sing and he can too.
• I have not read it, but I will read it. → I have not read it, but I will.
• He says he paid. He has not paid. → He says he paid. He hasn't.

If the sentence has no auxiliary, do steps in, exactly as it does in questions and in question tags:

• She works harder than he works. → She works harder than he does.
• I did not enjoy it, but my wife enjoyed it. → I did not enjoy it, but my wife did.

This is the same auxiliary system that runs tags and short questions, doing one more job. Once you see that do, have, be and the modals are the load-bearing words of English, half of this page follows automatically.

Short answers

Short answers are ellipsis in its purest form: subject plus auxiliary, nothing else.

Two details matter. First, a positive short answer is never contracted: Yes, I do, not Yes, I'd - there is nothing to contract onto. Second, plain yes and no on their own can sound short-tempered in British English. The auxiliary is what makes the answer polite: No, I haven't is an answer, No is a door closing.

so and not after think, hope and be afraid

When the missing part is a whole clause, the stand-in is so:

• Is she coming? - I think so. (= I think that she is coming)
• Will we make it? - I hope so.
• Is this the right road? - I suppose so.

The negative splits the verbs into two camps, and learners mix the camps daily.

Camp one carries the negative on the verb: think, suppose, expect, imagine. You say I don't think so, and I think not belongs to costume drama.

Camp two puts the negative on the clause, so so becomes not: hope, be afraid, guess. You say I hope not and I'm afraid not, and you cannot say I don't hope so at all.

• Will it rain? - I hope not. (there is a picnic)
• Is there any tea left? - I'm afraid not.
• Do we have to pay again? - I don't think so.

I'm afraid so and I'm afraid not are worth learning as fixed politeness tools: they are how British English delivers bad news in four syllables.

so do I, neither do I

To agree with what somebody just said, echo the auxiliary and flip it in front of the subject:

• I love this song. - So do I.
• I'm freezing. - So am I.
• I've been here before. - So have I.

Agreeing with a negative statement swaps so for neither (or nor, which is the same thing in a slightly better coat):

• I can't hear anything. - Neither can I.
• I didn't sleep well. - Neither did I.
• I won't say a word. - Nor will I.

The auxiliary must match the original statement, which means you have to hear it before you answer - So did I after a past simple, So would I after a would. The inversion here is the same word-order flip covered in inversion and word order: a negative or restrictive word at the front drags the auxiliary over the subject.

In relaxed speech, me too agrees with positives and me neither with negatives, and both are fine. What you cannot do is answer a negative with so: I can't swim. - So can I means you cannot have understood.

one and ones

When a countable noun has just been said, English swaps it for one rather than repeating it:

• Which cup do you want? - The blue one.
• These shoes are tired. I need some new ones.
• We looked at two flats: a big one with no light and a small one with a garden.

Rules of engagement:

1. Countables only. Wine, bread, money and other uncountable nouns do not take one: not the white one about wine but the white, or repeat the noun.
2. After adjectives, one is usually compulsory. The blue on its own does not survive as an answer about cups; the blue one does.
3. After this, that, these and those, one is optional in the singular (this one or this) and dropped in the plural (these, not usually these ones, which some British speakers say and some correct).

do so, and answering with nothing at all

Formal English has one more substitute worth recognising: do so stands for a whole action just mentioned. I asked him to move the car, and he did so at once. In speech it often shrinks further, to plain did. You mostly need do so for writing; reaching for it in conversation sounds like a police report.

And at the far end of the scale, speech deletes the beginnings of sentences entirely. Sounds good. Ever been to Wales? Shame about the weather. Each of these has lost its subject, and sometimes its auxiliary too, and each is perfectly normal spoken English. You do not need to produce these from day one. You do need to know that Sounds good is not a broken sentence, so that you stop mentally repairing other people's English while they talk.

Common mistakes

Ranked by how often learners actually make them.

1. Answering with the full sentence. Do you like it? Yes, I like it is grammatical and unnatural. Train the reflex: auxiliary only. Yes, I do.
2. I think yes. The stand-in for a clause is so, never yes: I think so. Same for the negative: I don't think so, not I think no.
3. I don't hope so. Hope will not carry the negative. It goes on the clause instead: I hope not.
4. So I do for So do I. The auxiliary must come before the subject when you agree with somebody else. Plain order means something different: so + subject + auxiliary is surprised agreement about yourself. You've got paint on your face. - So I have! The word order is the entire difference between "me too" and "oh, so I have".
5. Answering a negative with so. I didn't like it. - So did I is a contradiction in a party hat. Negative statements take neither did I.
6. One for uncountables. I prefer the red one about wine should be the red. If you cannot count it, one cannot stand for it.

Practice

Reply using as few words as the grammar allows. Answers are below.

1. Have you been to Scotland? - Yes, ___.
2. Is the bank open today? - I'm afraid ___.
3. I can't stand this music. - ___ (agree with the speaker).
4. Do you want the big box or the small box? - The small ___.
5. She promised to call, but she ___ . (she did not call)

Answers: 1. I have 2. not 3. Neither can I (or Me neither) 4. one 5. didn't (the auxiliary alone carries the missing verb)

The machinery on this page - auxiliaries standing for whole verb phrases - is the same machinery behind question tags, and the agreement patterns lean on the flip described in inversion and word order. If the auxiliaries themselves are still wobbly, start with modal verbs and come back: ellipsis is a reward for knowing them cold.