Auxiliary verbs in English are be, do, have and will. They function as auxiliaries when followed by another verb (independent) in order to form a question, negative sentence, complex sentence, or passive voice.
It can be both auxiliary and independent.
As an auxiliary
The verb do in English is used as an auxiliary in negative and interrogative sentences for most independent verbs (except be, will, have got and modal verbs) in Simple Present and Simple Past. (the infinitive is used for the independent verb)
In negative sentences:
- Simple Present: He does not play football.
- Simple Past: He did not play football.
In questions:
- Simple Present: Does he play football?
- Simple Past: Did he play football? The verb do is irregular:
- Simple Present: I / we / you / they do, he / she / it does
- Simple Past: I / he / she / it / we / you / they did
In the following cases in English the auxiliary verb do is not used in negative and interrogative sentences:
As an independent verb:
- I am not angry. / Are you okay?
In sentences that contain another auxiliary verb:
- They are not sleeping. / Have you heard that?
In sentences containing a modal verb (can, may, must, need, ought to, shall, should):
- We need not wait. / Can you repeat that, please?
When the question refers to the subject of the sentence:
- Who sings that song?
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