An auxiliary verb is a verb that is used together with a main verb to show time and continuity. Be and have are the primary auxiliaries. A primary auxiliary is used to construct compound tenses.
- Be is used to make present continuous and past continuous tenses
I am working.
Rob is using the computer.
We were all wondering about that.
Kevin was teaching in America in 2016.
- Be is also used for the passive.
These books are sold in supermarkets.
Martin was arrested and held overnight.
- Have is used to make present perfect and past perfect tenses.
Stephen has finished fixing the car.
George and Alice have seen the show already.
Amanda had already eaten when we arrived.
They had not expected to see us there.
- Do is the supporting auxiliary. It is used in forming negatives, questions, and emphatic statements.
I do not like sausages at all.
Do you like prawns?
You do like prawns, don’t you?
- Will, would, may, might, can, could, shall, should, and must are examples of modal auxiliary verbs, usually called simply, modal verbs. A modal verb allows us to talk about actions as possible, doubtful, or necessary.
Charlie will go home on Friday.
Charlie may go home on Friday.
Charlie could go home on Friday.
Charlie must go home on Friday.
Auxiliaries can be combined together in a single verb phrase. For example, a verb phrase may consist of a modal + a form of have + a form of be + a form of a main verb.
I could have been making a bad mistake by trusting him.
Sara will have been living in New Zealand for 2 years next month.
You must have been given the wrong number.
The auxiliary verb, or if there is more than one of them, the first auxiliary verb, performs these following grammatical functions:
- It shows tense and is the finite part of the verb phrase.
I have seen it.
She had seen it.
She has been thinking.
She had been thinking.
- It shows number and person agreement with the subject.
She has seen it.
They have seen it.
I am looking for it.
You are looking for it.
- It will take any negative immediately after it.
I do not want to do that.
She has not been concentrating.
- It can come before the subject to make a question.
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