Auxiliary Verbs: What Are Auxiliary Verbs? Definitions and Examples

By Carly Forsaith, updated on April 28, 2023

Are you wondering what auxiliary verbs are? Look no further. In this article, you'll learn what they are, what their purpose is, and how to use them.

In short, auxiliary verbs have three main functions: 

  • To form tenses
  • To indicate mood
  • To form the passive voice

This guide is part of our free online Grammar Book.

What Are Auxiliary Verbs?

Let's begin by defining what auxiliary verbs are. It's important to understand exactly what they are before we get into how to use them.

First of all you should know that there are three most common auxiliary verbs.

These are:

  • be
  • have
  • do

That's just the verbs in their infinitive form. When using them in a sentence, ensure subject-verb agreement by conjugating the verb correctly according to the noun or pronoun that makes up the subject.

Auxiliary verbs only work if combined with another verb, called the main verb. For this reason, auxiliary verbs are also called 'helping verbs' - because they help the sentence's main verb.

Note that the auxiliary verb usually comes before the main verb in a sentence.

It's possible for a sentence to contain more than one auxiliary verb.

A Word About Modal Verbs

Modal verbs are a special type of auxiliary verb that indicates possibility, intent, permission, or obligation.

Here are the most commonly used ones:

Modal verbs form certain tenses and moods, as you'll soon find out.

Interestingly, modal verbs don't have a subject-verb agreement. They always keep their original form regardless of the sentence's subject. Case in point with the verb 'should:'

I should
You should
She should
We should
They should

Now we know what auxiliary verbs are, let's move on to their function. What exactly are they for?

Well, it turns out that auxiliary verbs have three main functions. But they do more than just three things, which we'll also cover.

Three Main Functions for Auxiliary Verbs

Let's begin with an auxiliary verb's three main functions. Auxiliary verbs are used with a main verb to express:

  • tense,
  • mood,
  • or voice.

To Form Tenses

The first thing that auxiliary verbs are super handy for is forming tenses. In fact, without them, you would only be able to form the present and past indefinite tenses and none of the others.

I will list each of the tenses that need an auxiliary verb and examples to go with it. You'll see the auxiliary verb underlined.

The future tenses are the only tenses to use a modal verb ('will').

You will visit him later this week. (future indefinite)

I will be visiting him later this week. (future continuous)

She will have given out free samples. (future perfect)

We will have been here three years. (future perfect continuous)

The other tenses use the auxiliary verbs 'be' and 'have.' That includes the present tenses:

They are visiting him now. (present continuous)

She has given out free samples. (present perfect)

We have been here three years. (present perfect continuous)

And the past tenses:

They were visiting him. (past continuous)

She had given out free samples. (past perfect)

We had been here three years. (past perfect continuous)

To Indicate Mood

The other thing auxiliary verbs are great for is indicating mood. Verb mood, if you're not sure, indicates tone. The mood of a verb can tell us whether the speaker intended to give a command, make a request, express a wish, and many more things.

Below I'll list a sentence in each mood (there are five), and I'll underline the auxiliary verb for your reference.

South Africa is ahead in the competition. (indicative sentence)

Don't sit there! (imperative sentence)

I wish you would be quiet. (subjunctive sentence)

If he was rich he would buy a castle. (conditional sentence)

Do you know him? (interrogative sentence)

To Form the Passive Voice

In English grammar, there are two voices: passive and active. The passive voice gets a lot of criticism, and you should indeed limit your usage of this voice. However, it has its place. Auxiliary verbs are necessary for forming the passive voice. Specifically, the auxiliary verb 'be,' combined with the past participle of the main verb. Read on for some examples.

Dogs were found to be very calming for employees.

The office has been refurbished.

My son was bitten at school.

Other Functions for Auxiliary Verbs

Now we've covered the three main functions of an auxiliary verb, let's take a look at the other stuff it can do.

For Questions

Auxiliary verbs have two functions in questions: to add a question tag or to ask closed questions. 

Question tags are a way to check if a statement is correct. Here's an example of a question tag formed using the auxiliary verb 'are':

You're going to introduce yourself, aren't you? 

Because the statement is positive, the question tag is negative. If the statement were negative, the question tag would be positive. For example:

You're not going to introduce yourself, are you?

Here's an example of a question tag that uses 'do':

You do like me, don't you?

And here's one that uses 'have:'

You don't have a lighter, do you?

Notice that the auxiliary verb in the question tag is always the same as the one in the main statement unless the main statement doesn't contain an auxiliary verb, in which case you'd use the verb 'do':

You really want to go home now, don't you? 

To Avoid Repetition

Do you know how you can replace nouns with pronouns to avoid repeating a noun over and over again? Well, you can use auxiliary verbs to avoid repeating a verb. For example, a sentence like the following looks a little clunky:

My orchid plant is growing quite well but my roses are not growing.

Instead, it's completely acceptable to remove the main verb 'growing' and just shorten it to the auxiliary verb 'is.' Or, in this case, 'isn't,' since it's a negative statement. So it would look like this:

My orchid plant is growing quite well but my roses are not.

Here's another example where the negative statement comes first and is followed by a positive statement:

I am not a fan of watching sports on TV but Rosie is. 

Mind you, these sentences don't have to have a negative and a positive statement.

My daughter does gymnastics and so does yours. 

But what about if there's no auxiliary verb in the sentence? Then what would you use? Take the following sentence, for example, there's the main verb 'like,' and that's it; there's no auxiliary verb. So instead of having to repeat the verb 'like' and saying:

Mary likes candy and Jill likes candy. 

What can you say? Easy! Just use 'do.' Like this:

Mary likes candy and so does Jill.

To Form Negatives

Forming a negative statement is pretty easy. You add 'not' between the auxiliary verb and the main verb. For example:

I am not joining you for dinner.

But what if there is no auxiliary verb in the sentence? You can't possibly put 'not' between the auxiliary verb and the main verb if there is none. Take the following sentence:

She knows the way to the cabin.

The only verb is the main verb, 'know.' There's no auxiliary verb. Don't worry! This is where auxiliary verbs come in. You can use auxiliary verbs to form negative statements in these special circumstances.

All you have to do is add an auxiliary verb yourself. The auxiliary verb 'do,' to be precise. And don't forget the 'not,' of course.

She does not know the way to the cabin.

To Emphasize

There's one more way you can use auxiliary verbs, and that's to create emphasis. An auxiliary verb followed by an infinitive is a great way to emphasize the verb. Specifically, this works with the auxiliary verb 'do.' For example, imagine you're at the dentist, and she reprimands you for not washing your teeth three times a day. You might answer:

I do brush my teeth three times a day!

You'll often use them in this way to respond to someone else's statement if you want to prove them wrong or say the opposite of what they have said. Or you can use it in a standalone statement. Say, for instance, you're eating a piece of chocolate and enjoying it; you might say:

I really do love chocolate. 

Note that when you say these sentences out loud, you'll emphasize the auxiliary verb. To do this, you can say it louder or for longer. Often also, they'll be italicized when written down. This is difficult to exemplify in this article since we italicize all the words in our examples, but if we didn't, it would look like this:

I do take it seriously!

Concluding Thoughts on Auxiliary Verbs

Well, that pretty much concludes this article on auxiliary verbs. Hopefully, by now, you feel confident in your knowledge and understanding of how to use them. Let's summarize what we've learned:

  • Auxiliary verbs have three main functions: to form tenses, affect mood and create the passive voice.
  • They also have four minor functions: in questions, to avoid repetition, to form negatives, and to create emphasis.
  • There's a special type of auxiliary verb called 'modal verb.' 

If you found this article helpful, you might like the others we have in our free online Grammar Book. It's a database where you'll find heaps of grammar articles that break down complex grammatical concepts in accessible ways. Check it out!

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Written By:
Carly Forsaith
Carly Forsaith is one of the lead freelance writers for Carly is a copywriter who has been writing about the English language for over 3 years. Before that, she was a teacher in Thailand, helping people learn English as a second language. She is a total grammar nerd and spends her time spotting language errors on signs and on the internet.

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