Difference Between Modal and Auxiliary Verbs

Main Difference – Modal vs Auxiliary Verbs

Modal verbs and auxiliary verbs are verbs that help other verbs to show meaning. Auxiliary verbs indicate information such as tense, mood, voice and other grammatical aspects of the action. Modal verbs are a type of auxiliary verbs that indicate the modality. The main difference between modal verbs and auxiliary verbs is that modal verbs are not subject to inflection whereas auxiliary verbs change according to tense, case, voice, aspect, person, and number.

What are Auxiliary Verbs

Auxiliary verbs are verbs that help the main verb to show its tense or form negation or questions. They add extra information to the main verb such as time, tense, grammatical aspect, modality, voice etc. There are three common helping verbs in the English language.

Be: am, is, are, was, were, etc.

Do: do, does, did, etc.

Have: has, have, had, etc.

To understand the importance of auxiliary words more clearly, examine the sentences below carefully. The auxiliary word is underlined in these sentences.

She didn’t like him.

They are not helping us.

Has she completed the project?

She was playing basketball.

He has bought a new house.

However, it is important to know that these verbs (do, have and be) can also occur as action words or linking verbs. If the verb stands alone in a sentence, not followed by another verb, then it is not functioning as an auxiliary verb.

He has a huge stomach. – Action verb

She is pretty. – Linking verb

Difference Between Modal and Auxiliary Verbs

She was playing Basketball.

What are Modal Verbs

Apart from the verbs mentioned above, there is also a separate category of auxiliary verbs known as Modal verbs. This category includes Can, Could, May, Might, Must, Ought to, Shall, Should, Will, and Would. Modal verbs are a category of auxiliary verbs and are often known as modal auxiliary verbs. These verbs are used to indicate modality. They can express possibility, probability, ability, permission, obligation, etc.

He can sing beautifully.

It might rain tomorrow.

They might not attend the meeting.

Marlene ought to buy a new phone.

I will complete this tomorrow.

Would you like to have a cup of coffee?

Modals verbs are never used with other auxiliary verbs such as do, be, and have. The negative is formed by simply adding not after the modal verb, and the interrogative is formed by the inversion of the subject and the verb. Unlike auxiliary verbs, modal verbs never change form; they cannot be inflected.

Main Difference - Modal vs Auxiliary Verbs

He can sing beautifully.

Difference Between Modal and Auxiliary Verbs


Modal Verbs are auxiliary verbs that express modality.

Auxiliary Verbs are verbs that help the main verb to express tense, grammatical aspect, modality, voice, etc.


Modal Verbs indicate possibility, probability, ability, permission, obligation, necessity, etc.

Auxiliary Verbs indicate the tense, mood, grammatical aspect, etc. of the main verb.


Modal Verbs are not subject to inflections.

Auxiliary Verbs are subject to inflections.


Modal Verbs in English include Can, Could, May, Might, Must, Ought to, Shall, Should, Will, and Would.

Auxiliary Verbs in English include Be, Do, and Have.Difference Between Modal and Auxiliary Verbs- infographic

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