To do — auxiliary verb

Inflexions

• Base form = do
• Present form = do/does
• Past form = did
• Present participle/gerund = doing
• Past participle = done

To make questions with normal verbs. This also includes question tags

To do is used to make interrogatives in English. We use to do to make interrogatives with all normal verbs, that is, all verbs that aren’t auxiliary or modal auxiliary verbs.

Such normal verbs are, for example, make, clean, study, build, write, play, eat, sing etc. Do is a general-purpose verb for making questions in English. I.e., does she like to play football? Do you own a car? Did they pass their exam?

• Does Sally like to play the piano? Yes, she likes to play.
• Did you do your homework yesterday?
• Does she play soccer?
• George writes poetry, doesn’t he? (question tag)
• They go to school, don’t they? (question tag)

If a sentence starts with another auxiliary verb, then the question tag following it must use the same verb as the auxiliary verb. Negative to positive or positive to negative. I.e,

• I can’t see you, can I?

Question tags

To do is used to form question tags with normal verbs. Question tags are used instead of normal questions when we already assume the answer. For example,

• Christina loves her children, doesn’t she?

‘Doesn’t she’ is the question tag. Because love is a normal verb, it requires the auxiliary verb do in the question tag. Another example of a question tag,

• She didn’t like me, did she?

Did she? is the question tag.

In order to be extra emotive or put more emphasis on the sentence.

To do is used to be extra emotive, that is, we can insert do into our sentences to add more emphasis or emotion. She did call me instead of, she called me. I.e., I did not arrive late yesterday instead of, I didn’t arrive late yesterday.

In this case, the contraction (didn’t) is avoided to give more emphasis. It is only used as an emphasis with ordinary verbs and not other auxiliary verbs.

• Did you do your homework last night? Yes, I did do my homework last night.
• I did not appreciate it when those people spoke loudly.
• They did not have any idea about the situation at all.
• By not using a contraction, the verb ‘do’ is automatically used for emphasis.

To negate, that is, to make sentences or questions negative. But not with other auxiliary verbs.

To do is used to make sentences or questions negative. However, we cannot use do to make other auxiliary or modal auxiliary verbs negative.

We can only use do to negate ordinary verbs. Therefore, it is incorrect to say, I don’t can go. Can is a modal auxiliary verb and takes the adverb not.

Therefore, you would need to say I can’t go. The correct usage of do for negation would be I don’t like cricket. She doesn’t want to come.

• I don’t like tomatoes.
• Do you look up to the sky at night? No, I don’t look up to the sky at night,
• I don’t like maths.
• Did you go out to the party last night?
• Doesn’t he know anyone in the neighbourhood?
• Did you do your assignment?

Therefore, it is wrong to say: ”I don’t can go” or ”She doesn’t must pass the exam”. We use ‘do’ to negate ordinary verbs NOT auxiliary verbs. 

Note that in the last example the first ‘to do’ in the sentence functions as an auxiliary verb and the second ‘do’ in the phrase functions as an ordinary verb. So ‘do’ works both as an auxiliary and an ordinary verb.

We use it as a shortened verb form or like a sort of ellipsis

• Did she play tennis last night? Yes, she did. (instead of; ‘yes, she did play tennis…)
• Do you like playing rugby? No, I don’t. (instead of; ‘no, I don’t play…)
• Does he act strangely? Yes, he does. (instead of; ‘yes, he does act strangely)

We already assume the recipient knows what we’re talking about, so it’s not necessary to complete the whole phrase again. 

A quick lesson with context and analysis

• Did you catch up¹ with Sophie² over the weekend, Maria?
• Yes, I did catch up with her³.
• So, what did you guys do then⁴? Anything special?
• Well, first, we really needed to catch up with each other because it’s been so long since we last spoke. We went out for some drinks in the city centre before finally going to a disco.
• I suppose you two drank a lot then, didn’t you⁵?
• Well, yes, I guess we shouldn’t have drunk⁶ so much, but hey, once in a blue moon⁷ doesn’t hurt⁸.
• So, what’s the latest with Sophie? She’s working in consultancy, isn’t she^9,10?
• Yes, spot on¹¹. Plus, she’s also taking a year off¹² next year to go abroad.
• Wow! Really? Where is she going to go to?
• She said she was going to South America.
• I suppose she’ll be travelling, won’t she¹³?
• Yes, basically.
• Very interesting. Sounds like you two had a nice time last night. Good to see you’re catching up with everyone.
• Me too.

Analysis

1. Did you catch up with Sophie? The phrasal verb catch up basically means “to see someone that you haven’t seen for a while”. It could be the first time you’re seeing that person in a long time.
2. Did you catch up… We use the past form of do in the past, (did) because we’re asking a question about a past action. I.e., did they see you on Tuesday?
3. Yes, I did catch up with her. Did is being used to be extra emotive. As a normal answer it would be I caught up with her.
4. So, what did you guys do then? Do is both an auxiliary verb and a normal verb. In this example, did is the auxiliary form because did is asking a question in the past. Do functions as an ordinary verb here. In another example you could say, what do you like to do? The first do acts like an auxiliary verb while the latter do works as an ordinary verb.
5. I suppose you two drank a lot, didn’t you? This is a question tag. Suppose is an ordinary verb so therefore, it takes the auxiliary verb do in the question tag. With question tags, it’s positive to negative or negative to positive.
6. Drink-drank-drunk. The infinitive = drink. The past simple = drank, and the past participle = drunk. I.e., I like to drink wine. I drank some wine. I have drunk some wine.
7. Once in a blue moon. An expression meaning that something doesn’t happen very often.
8. Once in a blue moon doesn’t hurt. Do is being used to negate/make negative this sentence. Hurt is an ordinary verb, therefore, it needs the auxiliary verb do to be negated.
9. She’s working in consultancy. The present continuous is used here because we can use the present continuous in English to talk about actions that happen in the moment, or even permanent states. I.e. I’m working at English Reservoir.
10. She’s working in consultancy, isn’t she? ‘s, which is the contracted form of the auxiliary verb be (in third person singular) is used, therefore you can’t use do in the question tag. You must use the auxiliary verb, be.
11. Yes, spot on. An expression in English meaning that something or someone is correct.
12. Plus, she’s also taking a year off. The present continuous (be + verb + ing) is used here to talk about an action that will happen in the very near future.
13. I suppose she’ll be travelling, won’t she? The auxiliary verb will is forming part of the question tag because the auxiliary verb to begin with is will.

See also