Modal Verbs vs. Auxiliary Verbs

Modal verbs and auxiliary verbs are verbs that help other verbs show meaning. In this lesson, we will learn their differences.

What Is Their Main Difference?

The main difference between modal verbs and auxiliary verbs is that modal verbs do not change their appearance while auxiliary verbs change according to certain factors in the sentence.

Modal verbs (also known as modals and modal auxiliary) are a group of verbs that give additional information about the function of the main verb. Modal verbs are a type of auxiliary verbs. We have nine modals in English:

Here are some examples so we can see modals in action:

He can stay and watch the procedure.

I would try a different route.

Auxiliary Verbs

Auxiliary verbs (also called the helping verbs) are verbs that are paired with a main verb to create tenses and voices. We have four auxiliary verbs in the English language:

In the following examples, we have the auxiliary verbs 'do' and 'be':

I don't like Yoga.

Janet is going on a vacation.

Tip!

'Will' is a modal auxiliary verb. There is confusion around it as it functions like an auxiliary, but it is not an auxiliary verb. 'Will' is sometimes counted as an auxiliary verb to make it easier for learners to understand when it expresses the future tense.

She will stay for the main event.

At this pace, we will be late for the party.

Similarities

With Main Verbs

Both auxiliary verbs and modals must be used with the main verb and cannot be used alone (unless there is a short answer such as "I can." and "I am."). Have a look:

I shall send him a letter. (Not "I ~~shall~~ him a letter.")

She has been talking when they called. (Not "She ~~has~~ ~~been~~ when they called.")

Negation and Questions

Much like auxiliary verbs, modals can create a negative sentence. In this case, we add 'not' to the modal or the auxiliary verb. For example:

I cannot finish all of these candies by myself.

I don't got any clues.

We can also ask questions using modals and auxiliary verbs. To do so, we invert the modal or the auxiliary. Look:

She is waiting for me. → Is she waiting for me?

She could be a threat. → Could she be a threat?

Tip!

When our sentence consists of a modal verb and more than one auxiliary verb, the head of the sentence will be the modal verb and when making the sentence negative, we add 'not' to the modal verb. Watch:

I may have been trying to reach her. → I may not have been trying to reach her.

Differences

Function

Modals are used for communicative purposes such as:

Talking about possibilities, probabilities, etc.
Asking for advice, permission, etc.
Talking about habits

I may have texted the wrong number.

Here, we are talking about a possibility.

You should consider buying a new car.

Here, we are suggesting something.

Auxiliary verbs, however, are used to help express the main verb's:

Harry is studying law.

Here, we have the auxiliary verb 'be.'

She has been helping me with work.

Here, we have the auxiliary verb 'have.'

Conjugation

Modals cannot be conjugated, and the only way to conjugate them is to use their base form. Auxiliary verbs, however, can be conjugated. They change their appearance according to the subject or tense. Take a look at the following examples:

Ariana must have been here on time. (Not "Ariana ~~musted~~ be here on time.")

She was late yesterday.

With Other Verbs

Modals can be used with as many auxiliary verbs as possible in one sentence:

I should have visited her more.

'Should' is a modal verb and 'have' is an auxiliary verb.

You can also use several auxiliary verbs in one sentence:

She hasn't been running as much as se used to.

However, we cannot use multiple modals in one sentence. You can only use one:

She could help you. (Not "She ~~will~~ ~~could~~ help you.")

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