The auxiliary verb do is used along with a main verb to give emphasis to positive statements.
- I do like carrots!
- You do know the man I’m talking about!
- He does want to come with us!
- I said I would give him the money and I did give him the money!
Note, however, that you cannot use do in this way to emphasize the lexical verb be, nor any auxiliary verb.
When parts of a sentence are omitted because they can be understood from what has already been said, this is known as ellipsis. Ellipsis avoids unnecessary repetition of information.
When some parts of a sentence are left unsaid in this way, an auxiliary verb may be all that remains of a verb phrase and the words that might have followed it.
- ‘Is she coming with us?’
- ‘Yes, she is.’ (= Yes, she is coming with us)
- ‘Can I come too?’
- ‘Yes, of course you can.’ (= Yes, of course you can come too)
- ‘Mary can speak Arabic.’
- ‘I think her brother can too.’ (= I think her brother can speak Arabic too)
- ‘Could I be of help?’
- ‘Yes, you probably could.’ (= Yes, you probably could be of help)
- ‘Have you broken my Walkman?’
- ‘No, I haven’t.’ (= No, I haven’t broken your Walkman)
- ‘Did you see John when you were in town?’ ‘Yes, I did.’ (= Yes, I did see John)
- ‘If you two will wash the dishes tonight, I will tomorrow night.’ (= I will wash the dishes tomorrow night)
Where there is more than one auxiliary verb available in the context, it is equally correct in ellipsis to keep either only the first one or else two or more of them:
- ‘Could he have escaped?’
- ‘Yes, he could.’ OR ‘Yes, he could have.’
- ‘Should he have been taking all those tablets?’
- ‘No, he shouldn’t.’ OR
- ‘No, he shouldn’t have.’ OR
- ‘No, he shouldn’t have been.’
Ellipsis of this sort requires the presence of an auxiliary verb. When there is no other auxiliary verb available in the context, the auxiliary verb do is again brought in to fill the gap:
- ‘You forgot it was my birthday!’
- ‘Yes, I know I did. (= I know I forgot)
- ‘He probably thought we were on holiday.’
- ‘Yes, I expect he did.
- ‘The cat possibly thinks its reflection in the mirror is another cat.’
- ‘Yes, perhaps it does.’
As might be expected, the lexical verbs be and have are again exceptions to the general rule, and do not need an auxiliary verb in an ellipsis. Be never takes an auxiliary, have may or may not do, depending on its sense:
- ‘Are you my son’s maths teacher?’
- ‘Yes, I am.’
- ‘Were the boys at school yesterday?’
- ‘Well, I think they were’
- ‘Have you enough money with you for your bus fare?’
- ‘I think I have.’ OR I think I do.’
Simple ellipsis is one way of avoiding unnecessary repetition of information. Another way is by using the word so, either with an auxiliary verb or with be, have or do.
When you say so do I, so can she, so did they, etc, you are saying that what is true of one person is equally true of another person:
- ‘I can ride a bike.’
- ‘Weil, so can I.’ (= I can ride a bike too)
- ‘Lynn will be at the party tomorrow.’
- ‘So will Donald.’
- ‘Mary speaks Arabic.’
- ‘So does her brother.’ (= Her brother speaks Arabic too)
- ‘I went to the Philippines for my holiday this year.’
- ‘Isn’t that amazing! So did I.’
- ‘Jane’s mother is a teacher.’
- ‘So is her father.’
The negative form of this construction uses neither.
- ‘I can’t ride a bike’.
- ‘Neither can I.’ (= I can’t ride a bike either)
- ‘Mary doesn’t speak Arabic.’
- ‘Neither does her brother.’
When you say so I am, so she did, etc, you are agreeing that what has just been said is true:
- ‘Timmy can ride a bike.’
- ‘So he can.’ (= I agree that Timmy can ride a bike)
- ‘Look! They’re all running away!’
- ‘So they are.’ (= You are right. They are running away)
- ‘Mary speaks Arabic.’
- ‘So she does.’ (= I agree that Mary speaks Arabic)
- ‘You put salt in the pudding instead of sugar!’
- ‘So I did. Silly me!’
- ‘You are a fool!’
- ‘Yes, so I am.’
Again the negative form of this construction uses neither.
- ‘Mary doesn’t speak Arabic.’
- ‘Neither she does.’ (= I agree that Mary does not speak Arabic)
- ‘You’re not being very sensible, you know.’
- ‘Neither I am.’ (= I agree that I am not being very sensible)
You can also use do so, does so or did so to avoid repeating words that have just been said:
- You asked me to tell them and I did so. (= I told them)
- The doctor said I should drink two litres of water a day, and I always try to do so. (= I always try to drink two litres of water a day)
- Since my mother made me promise to read the Bible every day, I have always done so.
- I had meant to talk to you about this before the meeting. Could I do so now?