Summary
In-depth Explanation
The most common auxiliary verbs are be, have, and do. Modal verbs such as can, could, may, might, must, shall, should, will and would also serve auxiliary functions.
Primary Auxiliary Verbs
The primary auxiliary verbs are be, have and do. They help form different verb tenses and structures, such as the continuous (or progressive) tenses, the perfect tenses and the passive voice.
Be: Used to form the continuous tenses and the passive voice.
She is reading a book.
We were talking on the phone.
Their meals are prepared by a professional chef.
The cake was baked by my sister.
Have: Used to form the perfect tenses, indicating actions completed at different times.
I have finished my homework.
He had already left before we arrived.
Do: Used to form questions, negatives and emphatic sentences in the simple present and simple past tenses.
Do you like coffee?
He didn’t come to the party.
I do like cake, just not carrot cake!
Modal Auxiliary Verbs
Modal auxiliary verbs are used to express modality, such as ability, permission, possibility, necessity and obligation. Unlike primary auxiliaries, modal verbs don’t change form based on the subject and are followed by the base form of the verb. Here are some examples:
Can: Used to express ability or possibility.
She can speak three languages.
Could: Used to make polite requests or to indicate a past ability.
Could you help me with this?
Must: Expresses a strong obligation, necessity or requirement.
You must wear a helmet when riding a bike.
Will: Used to indicate a future action or to make a promise or decision.
I will call you tomorrow.
Should: Used to give advice or make recommendations.
You should eat more vegetables.
Using Multiple Auxiliary Verbs
In some tenses, we use multiple auxiliary verbs together in one sentence.
For example, in the present perfect continuous tense we use the auxiliary verbs have (conjugated according to the subject) and been (the past participle of the verb be), along with the main verb in the -ing form. For example:
She has been working here for five years.
Similarly, we use the auxiliary verbs had been to form the past perfect continuous:
We had been working for an hour when our boss arrived.
In the future perfect continuous, we use the auxiliary verbs will be:
She will be arriving soon.
In the future perfect tense, we use the auxiliary verbs will have:
They will have finished the project by tomorrow.
Sometimes, we can even use three auxiliary verbs in one sentence. For example:
I might have been sleeping when you called.
She should have been studying instead of watching TV.
Could they have been waiting for us this whole time?