Modal Auxiliary Verbs

Written by tutor Karina G.

For reference for new ESL tutors: Often, ESL books unnecessarily use dense language to convey otherwise simple ideas and grammatical rules. It is important for us to break down that language and teach new grammatical concepts to our students using plain language and easy-to-follow rules.

This article is written specifically for ESL students studying American English.


Clause – A part of a sentence
Invert – Reverse the order
Interrogative Statement – Question
Modifies – changes to show meaning

Modal Verbs – Modifies a sentence to show obligation

Auxiliary Verb – Often called “helping verbs” as they add meaning to the clause of the sentence in which they appear.

What is a Modal Auxiliary verb?

A Modal Auxiliary verb is a type of irregular verb that is accompanied by an infinitive (simple) verb. The Modal Auxiliary verb shows the modality of the meaning of the sentence, which means that is shows the probability, ability, obligation, or permission.

Example: I will do my homework after school today.
Example: He must not forget to write his essay for class.

List of verbs:

Modal Auxiliary Verb Form Preterite-Present Form
Can Could
May Might
Must None exists
Shall Should
Will Would

When do I use a Modal Auxiliary verb?

There are four major reasons for using the Modal Auxiliary verbs:

1) To Show Probability/ Possibility: To show how sure we are of something.
a) Can: I can probably run five miles, but I am not sure.
b) Could: I could run five miles when I was a teenager, but I am not sure if I am still able to run.

2) To Show Ability: The ability to do something.

a) Can: I can run five miles.
b) Could: I could run five miles tomorrow as I am too busy to go running today.

3) To Show Obligation: Shows the responsibility or requirement to do something.
a) Must: My trainer told me that I must run every day to prepare for the marathon.
b) Should: My doctor told me that I should run three days a week for my health.

4) To Show Permission: Shows whether something is allowed.
a) May: Mother, may I please join a running club?
Response: No, you may not join the running club.

Response: Yes, you may join the running club.
b) Could: Mother, could I go for a run now? I have finished all of my homework.

How do I use a Modal Auxiliary verb?

Use Modal Auxiliary verbs only with the infinitive (simple) form of the verb. The infinitive follows immediately after the verb.
Example: I can run.
Do not use: I can running.

Do not use the word “to” after a Modal Auxiliary verb.
Example: I won’t run.
Do not use: I won’t to run.

Do not pluralize Modal Auxiliary verbs (do not add “s”). The verb stays the same with every pronoun in the third-person singular.
Example: He will run.
Do not use: He wills run.

Add “not” to make Modal Auxiliary verbs negative.

Example: She could not run.
Example: She must not run.

Invert (reverse) your sentence to make it an interrogative (question) statement.
Example: “He can run.” becomes “Can he run?”

Use the preterite-present to convey either the past or the future.
Example: He may have lost his phone.
This example could be used in the case where a friend may not answer his phone because you think it may be

Example: He may miss his flight.
This example could be used in the case where you think someone may be late arriving to the airport and will not

be permitted to board the airplane.

Modal Verbs Practice Quiz

Try to fill in the blank spaces correctly.

I have hurt my knee, so my doctor said that I ______________ run.

{must not|mustnot|mustn’t}
The weather is so beautiful that I _________ go for a run outside today.

I would like to run longer distances, so I _____________ probably go for a long run on Saturday.

I _________ run for ten miles if I make sure to run slowly.

I am not allowed to run in the race this weekend as my mother told me that I _________ participate.

{may not}
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