What is a Modal Auxiliary? The Function of a Modal Auxiliary.

– Introduction:

Auxiliary verbs are of two types. They are (1) Primary auxiliary (2) Modal auxiliary. In today’s lesson, we will take an in-depth look at what a modal auxiliary is, what role it plays in the sentence, and how it differs from the primary auxiliary.

– What is a modal auxiliary?

An auxiliary that is used with the main verb to express the attitude of the speaker by expressing modality — that is, possibility, likelihood, ability, permission, obligation, or future intention is called a modal auxiliary.

– Which auxiliary verbs are modal auxiliary?

The number of actual modal auxiliary verbs is nine. They are:

  • Shall —– should
  • Will —— would
  • Can —- could
  • May —- might
  • Must

The following words are also considered modal auxiliary because of their modal auxiliary properties, i.e. they are used as a modal auxiliary. They are:

  • Ought to
  • used to
  • be to
  • have to
  • be going to
  • had better
  • would rather
  • dare
  • need.
Modal Auxiliary

– Characteristics of modal auxiliary:

  1. The modal auxiliary verb has no meaning of its own. However, it strongly helps the main verb of the sentence to express different moods or attitudes of the speaker. This is the main feature of a modal auxiliary.
  2. The modal auxiliary verb has two forms, namely Present and Past. So, unlike the Primary auxiliary verb (Do, Be, Have), they are not used as the main verb themselves.
  3. After modal auxiliary verb, the main verb is always in base form. Modal auxiliary verbs never take ‘s’ / ‘es’, ‘ed’ or ‘ing’, regardless of the subject or tense of the sentence.
  4. A modal auxiliary does not need any other auxiliary to make a sentence of interrogative or negative.

– Uses of modal auxiliary:

Uses of shall and will:

‘Shall’ and ‘will’ are used to describe different aspects of the future. Such as:

1. – In describing future events:

To describe future events that we believe will happen in the future and which cannot be avoided unless something bad happens, we use ‘shall’ with 1st person (I and we), and ‘will’ is used with the rest of the persons.


  • My son will be fifteen on his next birthday.
  • You will see many different kinds of animals when you go to the zoo.
  • We shall be happy if you come over to my home.

But to describe general future events that may or may or may not happen, ‘will’ is used with all persons (I, we, you, he, she, they) in spoken form. ‘Shall’ is rarely or never used.


  • They will go to Germany next month.
  • I will learn French besides English.
  • We will try to find a new house for our living.
  • I will take the TOEFL test to be admitted to a University.

2. – Giving and receiving services:

In interrogative sentences, the speaker usually uses ‘shall’ to offer help or service to another.

And if the speaker requests help or service from someone else, ‘will’ is used.


  • Shall I carry your luggage upstairs?
  • Will you help me carry my luggage upstairs?
  • Will you teach me some more rules of English grammar?

3. -To express the wishes, intentions, and promises:

To express desire, intention, promise, and determination, ‘shall’ is used with the 1st person, and ‘will’ is used with the rest of the persons.


  • I will learn French however difficult it is. [The speaker expresses his determination or promise].
  • I promise I will help you. [The speaker is expressing a desire or promise to help him].
  • I will give you a new laptop if you do well at school. [The speaker here promises that if he does well in school, he will give him a laptop].

Uses of can:

1. – To express ability or power:

‘Can’ is used to express the ability to do something or to be able to do something.


  • William can speak four languages.
  • He can swim.
  • Flora can sing and dance.
  • Mark can run as fast as an athlete.

2. – Asking or granting permission:

‘Can’ is used to ask for permission or for giving permission to do something.


  • Can I take your grammar book, please?
  • Can I borrow your book for a day?
  • Can I help you to carry the box?
  • You can go now to join your friends in the field.
  • You can tell what happened yesterday with your friend.

Note: ‘may’ can be used instead of ‘can’ to ask or give permission. Using ‘may’ reveals extra politeness.


  • May I take your grammar book, please?
  • May I borrow your bag for a day?
  • You may forgive him if you want.

-To express request:

We can express our request using the modal ‘can’.


  • Can you teach me English grammar?
  • Can you help me solve this problem?

-To express possibility/probability:

‘Can’ is used to express the possibility of something happening.


  • The sky is cloudy. I can rain today.
  • He is studying hard. He can obtain a good grade.

Note: ‘may’ or ‘might’ can also be used instead of ‘can’ to express possibility. But the difference is: using ‘may’ will mean more possibility than ‘can’. And using ‘might’ will mean less possibility.

-Uses of Could:

1. -To express the ability to do something in the past:

To express the ability to do something in the past, ‘could’ is used. The ability which is no more.


  • When I was young, I could lift a heavy load.
  • I could run hour after hour when I was a boy.

2. – To take permission:

Used to get permission to do something with a polite request.


  • Could I have your residential address?
  • Could I talk to our college principal, please?
  • Could you lend me your pen for a while?
  • Excuse me,  could I just request you to do something for me?

Note: It is important to remember that polite requests could also be used with ‘would you’ / ‘would you please’ or ‘could you please’.


  • Would you / would you please / could you please lend me your pen for a while?

– To express possibility:

Any kind of possibility or probability can be expressed with ‘could’.


  • My friend could come today.
  • The rain could stay for some more days.
  • This year William could get a good job.

-Uses of ‘may’ and ‘might’:

1. – To take permission or to give permission:

‘May’ and ‘might’ are used to take permission, give permission, and to make any kind of request.


  • May / might I borrow your cricket bat for a day?
  • You may / might go there if you like.
  • I am very thirsty. May / might I have something to drink?

2. – Future possibility:

Both ‘may’ / ‘might’ can be used to indicate future possibilities. However, ‘may’ is used to mean more or good possibility, and ‘might’ is used to mean small or slim possibility.


  • My friend may come later today.
  • My friend might come later today.

3. – Present possibility:

May / might + be + verb-ing is used to express a possibility or conjecture about a present situation.


  • He may / might be reading now.
  • It may / might be snowing in New York now.

4. – To offer assistance or help:

‘May’ is used only to humbly offer any kind of assistance or help to a person. ‘Might’ is not or cannot be used in this case.


  • May I teach English grammar?
  • May I help you with your carrying your luggage?

5. – To express wishes:

Only ‘may’ is used for wishing good luck or praying to the Creator for someone. ‘Might’ is not used in this case.


  • May you all live long.
  • May God bless you, all.

Uses of ‘should’ and ‘ought to’:

1. – To give advice and to express an obligation:

‘Should’ and ‘ought to’ are used to give advice or express obligations and duties that apply to the future.


  • You should / ought to obey your parents, elders and teachers.
  • You should / ought to attend your duties.
  • You should / ought to learn English perfectly to get a good job.
  • If you are ill, you should / ought to take medical advice.
  • We should / ought to get him some gifts on his birthday.

2. – To take advice and instruction:

‘Should’ is used to take advice, instruction, and suggestion through asking questions. In this case, ‘ought to’ is not used.


  • What should I do now to tackle the situation?
  • Should I trust him when he is telling me that he will help me?

3. – To express possibility or likelihood:

‘Should’ is used to express possibility or likelihood or to expect something to happen or come true.


  • He should be a nice human.
  • England should win the final cricket match.
  • I should be able to learn English and French.

4. – To express gratitude, happiness, or joy:

‘Should’ is used to express gratitude, happiness, or joy for what one will do or has done something for another/others.


  • I should be grateful if you kindly teach me English.
  • We should be delighted to help you in getting into a new business.
  • I should like to thank you for what you have done for me.

5. – To get someone’s opinion:

To get someone’s opinion regarding any matter, ‘should’ is used.


  • Should I take a taxi to go to New York city?
  • Should I ask him for his help?

6. -To issue official orders / instructions:

‘Should’ is used in giving or issuing official orders or instructions.


  • Everyone should remain at his home during Covid time.
  • Students should attend online classes until a further order is issued.

-Uses of ‘would’:

1. – To describe any past events:

‘Would’ is used to describe any event or action that is a past.


  • When he was a little boy, he knew that he would succeed in life.
  • I thought he would come here, so I came here to meet him.

2. – To describe a past habit:

‘Would’ is used to talk about things that repeatedly happened for a period of time in the past, but now that is not done anymore. That is, past habit, action, or practice is expressed with ‘would’.


  • When we were school students, we would play cricket every afternoon.
  • When I was a child, I would watch cartoons and fairy tale movies.

Note: Here the phrase ‘used to’ can be used in place of ‘would’ to describe past habits.

3. – To ask somebody politely to do something :

‘Would’ is used to make a polite request to a person to do something for somebody.


  • Would you please open the window?
  • Would you please turn down the volume?
  • Would you teach me English grammar?
  • Would you please call me a doctor?

4. – To express desire or choice:

‘Would’ is used to know a wish, desire, or choice. It is also used to express one’s own wish, desire, or choice. That is, ‘would’ is used to say what you like, love, hate, prefer, etc.


  • Would you like a cup of coffee or tea?
  • My brothers would like to talk to you.
  • I would like to get my son admitted to a medical college.
  • I would like to learn English grammar very well.

Note: Here in the place of ‘would like’, ‘would love’, ‘would prefer’ can be used.

5. – To imagine the impossible or the unreal:

‘Would’ is used to express impossible, improbable, or unreal stuff. That is, ‘would’ is used if something is hypothetical or contrary to fact.


  • If I were you, I would wear this jacket for today’s party.
  • If I could go to the USA, I would be with you now.
  • What would you do if you stood first in the test?
  • If I were a millionaire, I would buy this apartment.

6. – To express opinion:

‘Would’ is used to express a personal opinion. The three verb words ‘think’, ‘say’, and ‘imagine’ are mainly used after ‘would’. Would + think/say/imagine + extension.


  • I would think / say / imagine that you would be successful in a different business.
  • I would think /say / imagine that you would do better in the athlete.

Uses of ‘must’:

1. – To express certainty:

‘Must’ is used to express certainty about a thing or a person.


  • This must be the right decision.
  • He must be a university student.

2. – To express necessity, requirement, and obligation:

‘Must’ is used to express needs, requirements, and strong obligations.


  • They must pass twelfth grade to get into medical school.
  • Students must pass the IELTS exam to get into a university in the UK.

3. – To give advice:

’Must’ is used to give any kind of advice to a person.


  • You are very intelligent. You must prosecute higher studies in medicine.
  • You must take some medicine for your flu.

4. – With admit/confess/say:

After ‘must’ the verb words ‘admit’ / ‘confess’ / ‘say’ can be used to put emphasis on what has been said. Must + admit/confess/say + extension.


  • I must admit / confess / say that he is really an intelligent boy.
  • I must admit / confess / say that I won’t forget what you did for me.

5. – To express assumption:

‘Must’ is used to express strong assumptions about something.


  • You must be very busy preparing your lessons.
  • Mark must be nearly 40 years old now.
  • There must be something wrong with his wife.

Uses of other verbs as a modal auxiliary:

-Use of ‘dare’:

The word ‘dare’ means ‘to take the risk’ It can be used in both main verb and modal auxiliary. This is why it is called semi-modal. As a modal auxiliary, it is used in interrogative sentences and in negative sentences.


  • William dare not say what he thinks.
  • He is so afraid that he dare not move.
  • Dare he give him a phone call?
  • I dare not tell him the truth.
  • Vanessa dared not go there alone.

-Use of ‘need’:

‘Need’ means to require. This verb can be used both as a main verb and as a modal auxiliary. Because of this, it is called semi-modal. As a modal auxiliary, it is used in interrogative sentences and in negative sentences.


  • You need not ask my permission to go there.
  • He need not wait any longer for me.
  • You need not talk to your parents.
  • Need I discuss the matter with my parents?
  • Need we wait any longer for him?
  • Need I say any more about this?

Use of ‘be to’ (am to/is to/are to/was to/were to):

Am to/is to/are to/was to/were to):

1. – To express future plan:

The present and future form of ‘be to’ is am to/is to/are to. They are used for any arrangement / plan for the future.


  • I am to go to New York City next week.
  • My friend is to give me a phone me later this day.
  • The President is to make a statement tomorrow.

2. – To tell someone what to do:

Am to / is to / are to is used to convey an order of a person or a higher official that what one should do.


  • You are not to come out of your home during Covid time.
  • All students are to wait until I get back.
  • You are not to create any noise while I am teaching.

3. – To take advice:

Am to / is to / are to is used to get advice on what can be done in a particular situation.


  • In this situation, what am I to do to tackle the situation?
  • What is he to do to get into a medical university?

– Was to/were to:

The past form of ‘be to’ is ‘was to’/’were to‘. They are used to mean what they were supposed to do in the past but didn’t.


  • Our college principal was to speak in our inauguration class.
  • We were to meet our English teacher.
  • They were to go to India for medical treatment.
  • My friend was to come later today.

Use of ‘be going to’:

Am going to/is going to/are going to:

(a) ‘Am going to’/ ‘is going to’/’are going to’ is used to express an intention/plan about the future.


  • I am going to see my parents later this week.
  • They are going to sing at Christmas.

(b) Am going to / is going to / are going to is used to predict the future based on what we see or understand now.


  • Look at the sky. It’s cloudy It’s going to rain.
  • My friend is a lawyer. He is going to help me providing legal advice.
  • You are studying hard. You are going to secure a place in the test.

Was going to / were going to:

In the past, a person decided to do something, but he did not do it. ‘Was going to’ / ‘were going to’ is used to describe such conditions.


  • I was going to tell him my plan, but I forgot.
  • They were going to travel by train, but they changed their decision.
  • They were going to help his friend but they changed their minds.

-Use of ‘have to (have to/has to/had to/shall have to/will have to):

‘Have to’/’has to’ is used to express the obligation of a present situation. In this case, ‘must’ can also be used instead of ‘have to’/’has to’. The difference is that when the speaker wants to express his strong feelings about the need of doing the work, it is better to use ‘must’.


  • We have to pay electric and gas bills regularly.
  • He has to complete his lessons before going to school.
  • We have to stop eating chocolate every day to avoid being obese.

To make this type of sentence negative, use don’t have to/doesn’t have to.

  • He doesn’t have to go there.
  • They don’t have to go there.

-Use of ‘shall have to’/’will have to’:

‘Shall have to’/’will have to’ is used to express future obligations.


  • I shall have to go there tomorrow to meet my friend.
  • You will have to learn all the techniques to secure the first position in the test.

To make this type of sentence negative, use ‘shall not have to’/’will not have to‘.

  • They will not have to/won’t have to go there.
  • I shall not have to think much to get the solution.

-Use of ‘had to’:

‘Had to’ is used to express past obligations.


  • I had to take his suggestion to get rid of the problem.
  • William had to go to his friend’s house to help him.

To make this type of sentence negative, use ‘did not have to’.

  • I didn’t have to take his suggestion to get rid of the problem.

-Use of ‘used to’:

‘Used to’ is used to express past actions or events that were done regularly but are not done now.

  • I used to have coffee and biscuits in the morning, but now I have only a cup of tea.
  • I used to go to the office every day, but now I work from home.

Use of ‘had better‘:

‘Had better’ + base verb is used to denote the actions about what a person should do in a particular situation. That is, it also denotes ‘a better choice’.

  • You had better ask your parents instead of taking the decision on your own.
  • You had better call Grandma or she’s going to be disappointed.
  • I had better complete my assignment before I go to sleep.

To make these sentences negative, use ‘not’ after ‘had better’.

  • You had better not ask your parents about this.
  • The train will arrive on time. You had better not be late.

To make these sentences interrogative, use the subject between ‘had’ and ‘better’.

  • Had I better speak to William?

Note: ‘Had better’ is used only in present/ future conditions and not in past. It is because ‘had better’ doesn’t have a true past tense. 

-Use of ‘would rather’:

‘Would rather’ is used to express a preference for something.

  • I would rather run than walk.
  • Mark would rather have coffee tea than tea.
  • I would rather do my assignment early than submit it late.
  • I would rather go by car than use public transport.
  • I would rather not tell a lie.

Rezaul Karim

Hi, my name is Rezaul Karim. I am an English teacher and founder of LearnEnglishWithRezaul.com. I work with non-native English learners to help them understand English grammar from basic to intermediate. I also help them improve their conversation skills, and communication ability and reduce their accent. I hope you may like my posts on this website, and if you really really feel that this page/website is useful for English learners, please happily share it for others to know.

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