Many learners of English sooner or later face the auxiliaries do/does and did. In this post we will discuss what they are, when to use them, and how to use them. In order to make it clearer, we will talk about the other auxiliaries as well.
What are do/does and did?
They are all auxiliary verbs. And what is an “auxiliary verb” you might ask. The word auxiliary itself means helping or supporting. And indeed, these verbs support the main verb of the sentence and give grammatical information about it:
She has finished the book. – “finished” is the main verb here and “has” is the auxiliary verb which helps the main verb become present perfect
I don’t like rain. – “like” is the main verb here and “do” is the auxiliary (in this case with “not”) which helps the main verb and the sentence to become a negative present simple sentence
Tom can play the piano. – “play” is the main verb here, and “can” is the auxiliary verb which gives the main verb the additional meaning of being able to
Types of auxiliary
As we can see above, there are different kinds of auxiliary verbs. Let us make three groups to understand them better:
1. Modal auxiliaries: can, could, may, might, must, will, would, shall, should
These are auxiliaries which have their own characteristic meaning which is added to that of the main verb. This meaning can be obligation, ability, possibility, probability, permission, request:
You must follow the rules. – obligation
Sue can swim. – ability
You may sit down. – permission
Once a sentence has a modal auxiliary, it is present in all three types of sentence alike: affirmative, negative, and question:
She can swim. / Can she swim? / She can‘t swim.
2. have/has and had
These are auxiliaries which have a purely grammatical function and no real meaning: they just help the verb and the sentence turn into the present perfect or present perfect continuous (have/has) tense; or into the past perfect or past perfect continuous (had) tense.
We have painted the room.
Before she left home, she had closed the windows.
Have you been to China?
Once a sentence has have/has or had, it is present in all three types of sentence alike: affirmative, negative, and question:
She has been here. / Has she been here? / She hasn’t been here.
Note: I / you / we / they + HAVE ; he / she / it + HAS
3. do/does and did
And they are the trickiest! They are also auxiliaries which have a purely grammatical function and no real meaning, they show that the sentence is in the present simple (do/does) or in the past simple (did) tense.
BUT: they only appear in questions and negatives, and don’t normally appear in affirmative sentences.
She goes to school by bus. – present simple affirmative, NO DOES
Does she go to school by bus? – present simple question, DOES
She doesn’t go to school by bus. – present simple negative, DOES
Note: I / you / we / they + DO ; he / she / it + DOES
I drove to New York. – past simple affirmative, NO DID
Did you drive to New York? – past simple question, DID
I didn’t drive to New York. – past simple negative, DID
Note: We use do/does and did in present simple and past simple only with verbs other than be. The verb be can be used in itself in questions and negatives (She is not here. / Were you there? etc.).
How to use do/does and did?
In the present tense, this auxiliary verb has two forms, do and does:
I / you / we / they + DO ; he / she / it + DOES
In its past form, it only has one form with all subjects: did.
The verb after these auxiliaries is always in the infinitive or base form:
so it doesn’t have an -s and is not in the past form.
In short: use do and does if you want a negative sentence or a question in the present simple.
Use did if you want a negative sentence or a question in the past simple.