Modal Auxiliaries: Definition, Types, Uses, Examples and Exercises

Modal auxiliaries are helping verbs that work alongside a main verb to express a speaker’s attitude toward an action or state: whether it is possible, probable, necessary, permitted or obligatory. Without modal auxiliaries, English loses its capacity to express the shades of meaning that make communication precise and human. ‘She goes to the doctor’ is a statement of fact. ‘She should go to the doctor’ expresses advice. ‘She must go to the doctor’ expresses possibility. The main verb stays the same in every sentence. The modal auxiliary does all the work of shifting the meaning.

This page provides the most comprehensive guide to modal auxiliaries available for students. It covers the precise definition, how many modal auxiliaries there are, the complete list of modal auxiliaries, types of modal auxiliaries and a comprehensive collection of modal auxiliaries exercises with answers.

 

Table of Contents

• What are Modal Auxiliaries?
• List of Modal Auxiliaries
• Rules for Using Modal Auxiliaries
• Uses of Modal Auxiliaries
• 10 Examples of Modal Auxiliaries in Sentences
• Modal Auxiliaries Exercises

 

What are Modal Auxiliaries?

Modal auxiliaries are a type of auxiliary (helping) verb that combine with a main verb to express meanings such as ability, possibility, permission, obligation, necessity and probability. They modify the meaning of the main verb rather than expressing an action themselves.

Types of Modal Auxiliaries

Types of modal auxiliaries can be categorised in two ways: by their grammatical classification and by the meaning they express.

Classification 1: By Grammatical Type

 

Grammatical Type	Members	Description
Pure modal auxiliaries (Central modals)	Can, could, may, might, must, shall, should, will, would	These share all the defining features: no inflection, no ‘to’ before the main verb, no ‘do’ in negatives and questions.
Semi-modal auxiliaries (Marginal modals)	Ought to, need, dare, used to, had better	These share some but not all features of pure modals.
Modal phrases (Periphrastic modals)	Be able to (like can), be going to (like will), have to (like must), be supposed to (like should)	These multi-word expressions function like modals but are formed differently.

 

Classification 2: By Meaning Expressed

This is the most useful classification for students and examinations:

 

Type by Meaning	Modal Auxiliaries	What they Express
Ability	can, could, be able to	Physical or mental capability
Permission	can, could, may, might	Asking for or granting permission
Possibility	can, could, may, might	Something that is possible or likely
Probability	must, should, ought to, will	How likely something is
Necessity/Obligation	must, have to, need	What is required or needed
Advice	should, ought to, had better	What is recommended
Request	can, could, will, would	Asking someone to do something
Offer	shall, will, can	Proposing to do something
Future intention	will, shall, going to	Plans and intentions
Habit (past)	would, used to	Things done regularly in the past
Conditional	would, could, might	What would happen if

 

Primary and Modal Auxiliaries: The Key Difference

One of the most commonly confused distinctions in English grammar is between primary and modal auxiliaries. Understanding this difference is essential for examinations and for correct grammatical usage.

Primary Auxiliaries

Primary auxiliaries are the verbs ‘be’, ‘have’ and ‘do’. They are called primary because they are the main helping verbs used to form tenses, questions, negatives and passive constructions. Unlike modal auxiliaries, primary auxiliaries can also function as main verbs.

 

Primary Auxiliary	As Auxiliary	As Main Verb
Be	She is reading. (auxiliary)	She is a doctor. (main verb)
Have	He has finished. (auxiliary)	He has a car. (main verb)
Do	Do you know? (auxiliary)	Do your homework. (main verb)

 

Modal Auxiliaries

Modal auxiliaries (can, could, may, might, must, shall, should, will, would) are helping verbs that express modality. They cannot function as main verbs. They always require a main verb to complete their meaning.

Key Differences between Primary and Modal Auxiliaries

 

Feature	Primary Auxiliaries	Modal Auxiliaries
Members	Be, have, do	Can, could, may, might, must, shall, should, will, would
Can be main verb?	Yes	No
Change for person/number?	Yes (is/are/am; has/have)	No (always same form)
Used with ‘do’ in negatives/questions?	Yes (for ‘do’ itself: doesn’t work)	No
Followed by	Various verb forms	Base form only
Express	Tense, aspect, voice	Possibility, permission, obligation, ability
Example as auxiliary	She has gone.	She can go.

 

A Sentence Showing Both

• She has gone → ‘has’ is the primary auxiliary, forming the present perfect.
• She may go → ‘may’ is the modal auxiliary, expressing permission or possibility.
• She has been working → ‘has’ and ‘been’ are primary auxiliaries forming the present perfect continuous.
• She might have gone → ‘might’ is the modal auxiliary; ‘have’ is the primary auxiliary.

 

List of Modal Auxiliaries

The following is the complete list of modal auxiliaries as used in Indian school English education.

 

 

The 9 Pure Modal Auxiliaries

 

Modal Auxiliary	Primary Use	Example
Can	Ability, permission, possibility	She can speak French.
Could	Past ability, polite request, possibility	He could run fast when young.
May	Permission, possibility, probability	You may leave now.
Might	Weak possibility, past possibility	It might rain today.
Must	Necessity, obligation, certainty	You must wear a helmet.
Shall	Future (with I/we), offers, suggestions	I shall meet you at noon.
Should	Advice, expectation, obligation	You should see a doctor.
Will	Future, determination, requests	She will finish the project.
Would	Polite request, past habit, conditional	Would you help me, please?

 

Semi-Modal Auxiliaries

 

Semi-Modal	Primary Use	Example
Ought to	Moral obligation, advice	You ought to apologise.
Need	Necessity (absence of)	You need not worry.
Dare	Challenge, courage	How dare he speak like that!
Used to	Past habit or state	She used to walk to school.
Had better	Strong advice or warning	You had better leave now.

 

Rules for Using Modal Auxiliaries

 

 

Rule 1: Modal Auxiliary + Base Form of Main Verb

Always use the base (infinitive without ‘to’) form of the main verb after a modal auxiliary.

• Correct: She can swim.

• Incorrect: She can swims / She can swimming / She can to swim.

• Exception: ‘Ought’ is always followed by ‘to’ + base form; ‘she ought to apologise’.

Rule 2: No Change in Form for Person or Number

Modal auxiliaries do not add ‘-s’ for the third person singular.

• Correct: He can play. She must go. It will rain.

• Incorrect: He cans play. She musts go. It wills rain.

Rule 3: No ‘Do’ in Negatives and Questions

To make negative sentences with modal auxiliaries, add ‘not’ directly after the modal. To form questions, put the modal before the subject.

• Negative: She cannot (can’t) swim. You must not be late.

• Question: Can she swim? Must you go now?

• Do NOT Use: Does she can swim? / She does not can swim.

Rule 4: Two Modal Auxiliaries Cannot be Used Together

Two modal auxiliaries cannot appear together in the same verb phrase.

• Incorrect: She will can go tomorrow.

• Correct: She will be able to go tomorrow. (use the modal phrase instead)

Rule 5: Modal Auxiliary + Have + Past Participle (Perfect Modal)

For past reference, modal auxiliaries are followed by ‘have’ + past participle.

• She must have left already. (certainty about the past)
• He could have won. (past possibility that did not happen)
• You should have called. (advice about the past)

 

Uses of Modal Auxiliaries

 

A. Uses of Modal Auxiliaries: Can

Can is one of the most versatile and most frequently used modal auxiliaries in English.

 

Use	Meaning	Example
Ability	To express physical or mental ability in the present.	She can speak three languages fluently. He can lift very heavy weights. Can you play the guitar?
Permission	To ask for or grant permission in informal contexts.	Can I borrow your pen? You can leave early today. Can we use our phones during the break?
Possibility	To indicate that something is possible in general.	Accidents can happen at any time. Exercise can improve your mood significantly. Learning a new language can be challenging.
Polite request (informal)	To make an informal request.	Can you help me with this? Can you pass me the salt?

 

B. Uses of Modal Auxiliaries: Could

Could is the past form of ‘can’ but has several distinct uses beyond simple past ability.

 

Use	Meaning	Example
Past ability	To express ability that existed in the past.	When I was young, I could run very fast. She could speak French before she moved abroad.
Polite request	More polite than ‘can’ for making requests.	Could you please help me with this problem? Could I speak to the manager?
Possibility	To indicate something that is possible (often less certain than ‘can’).	It could rain this evening. This could be the solution we were looking for.
Conditional	To express what would be possible under certain conditions.	I could help you if you asked me. She could do it if she tried harder.
Suggestion	To suggest a course of action.	You could try calling them directly. We could meet at the cafe instead.

 

C. Uses of Modal Auxiliaries: May

May expresses possibility, permission and probability.

 

Use	Meaning	Example
Permission (formal)	The most formal way to ask for or grant permission.	May I come in? You may leave once you have finished. Students may use calculators for this section.
Possibility	To indicate something is possible.	It may rain tomorrow. She may be right about this. He may have already left.
Probability	To express a reasonable likelihood.	The train may be delayed due to the weather. They may arrive late if traffic is heavy.

 

D. Uses of Modal Auxiliaries: Might

Might expresses weaker possibility than ‘may’ and is also used for past possibilities.

 

Use	Meaning	Example
Weak possibility	Less certain than ‘may’.	It might rain later. (less certain than ‘It may rain’.)
Past possibility	Often used to refer to something that was possible in the past.	He might have been at the meeting but I did not see him. She might have known about it earlier.

 

E. Uses of Modal Auxiliaries: Must

Must is the strongest modal auxiliary for expressing necessity and certainty.

 

Use	Meaning	Example
Necessity and obligation	To express what is required or necessary.	You must wear a seatbelt while driving. All students must submit their assignments by Friday. We must reach the station before the train leaves.
Logical certainty (deduction)	To express a strong conclusion based on evidence.	She has been working for twelve hours: she must be exhausted. He must be at home: the lights are on. This must be the best biryani I have ever had.
Prohibition (must not)	‘Must not’ expresses strong prohibition.	You must not talk during the examination. Children must not play near the construction site. You must not share your password with anyone.

 

F. Uses of Modal Auxiliaries: Shall

Shall is traditionally used with first person (I/We) to express future action, and with second and third person for offers, promises and determination.

 

Use	Example
Future (with I/We)	I shall meet you at noon. We shall overcome all difficulties.
Offers and suggestions (questions with I/We)	Shall I help you with that? Shall we go for a walk? What shall we do this weekend?
Determination or promise	I shall return and I shall be stronger. We shall never give up.
Rules and regulations (formal)	All members shall attend the annual meeting. Vehicles shall not park here.

 

G. Uses of Modal Auxiliaries: Should

Should is used for advice, expectation, obligation and probability.

 

Use	Example
Advice and recommendation	You should see a doctor about that cough. She should practise more if she wants to improve. You should apologise to her.
Moral obligation or duty	We should help those who are in need. He should take responsibility for his actions.
Expectation	The package should arrive by Tuesday. She should be here by now.
Conditional (formal)	Should you require further assistance, please contact us. Should he fail the test, he will need to retake it.

 

H. Uses of Modal Auxiliaries: Will

Will is primarily used to express future action, determination and requests.

 

Use	Example
Future action	She will finish the project by tomorrow. It will rain in the afternoon. They will arrive next Monday.
Determination or promise	I will do my best no matter what. He will not give up without a fight. I will call you as soon as I reach.
Request	Will you please close the window? Will you help me carry this?
Offer	I will get that for you. Will you have some tea?
Habitual action (present)	She will often spend hours reading in the garden. He will always find something to complain about.

 

I. Uses of Modal Auxiliaries: Would

Would is the past form of ‘will’ but has many distinct uses including polite requests, conditional sentences and past habits.

 

Use	Example
Polite request	Would you please help me with this? Would you mind closing the door?
Conditional	I would help you if I could. She would have passed if she had studied more. If it rained, we would cancel the picnic.
Past habit	When I was young, we would visit our grandparents every summer. He would always bring sweets when he came to visit.
Polite offer or invitation	Would you like some coffee? Would you care to join us for dinner?
Reported speech	She said she would come the next day.

 

J. Uses of Modal Auxiliaries: Ought to

Ought to is a semi-modal that expresses moral obligation and advice, similar to ‘should’ but slightly stronger.

 

Use	Example
Moral obligation or duty	You ought to respect your elders. We ought to help people in need. He ought to take better care of his health.
Advice (slightly stronger than ‘should’)	You ought to see a specialist about that. She ought to reconsider her decision.
Expectation	The results ought to be out by Friday. This ought to be sufficient for everyone.

 

10 Examples of Modal Auxiliaries in Sentences

 

 

The following are 10 examples of modal auxiliaries demonstrating a range of uses and forms. These examples cover the most important modal auxiliaries and their most common uses.

 

No.	Sentence	Modal Auxiliary	Use
1	She can speak Japanese fluently.	can	ability
2	Could you please lower your voice?	could	polite request
3	You may use the library after school hours.	may	permission
4	It might be too late to apply now.	might	weak possibility
5	All passengers must carry a valid ID.	must	necessity/obligation
6	Shall we begin the meeting now?	shall	suggestion
7	You should eat more vegetables and less sugar.	should	advice
8	She will present her findings tomorrow morning.	will	future action
9	Would you like to join us for lunch?	would	polite offer
10	You ought to apologise for what you said.	ought to	moral obligation

 

Modal Auxiliaries Exercises

A. Underline the modal auxiliary in each sentence and state its use.

1. She can solve any problem in minutes.
2. May I use your phone for a moment?
3. You must submit the form before the deadline.
4. It might snow in December this year.
5. Shall we go for a walk after dinner?
6. You should drink more water every day.
7. He will arrive by the evening train.
8. Would you like some more coffee?
9. You ought to be more careful with your things.
10. She could run very fast when she was young.

Answers:

1. can → ability
2. May → permission (asking)
3. must → obligation/necessity
4. might → weak possibility
5. Shall → suggestion/offer
6. should → advice
7. will → future action
8. Would → polite offer
9. ought to → moral obligation/advice
10. could → past ability

B. Fill in each blank with the most appropriate modal auxiliary from the box. Each word may be used more than once.

 

can

could

may

might

must

shall

should

will

would

ought to

 

1. You __________ not eat junk food every day: it is bad for your health.
2. __________ I borrow your textbook until Monday?
3. She __________ speak four languages when she was twelve years old.
4. It __________ rain this evening: the clouds are looking dark.
5. __________ we begin the presentation now?
6. All students __________ wear their uniforms on school days.
7. He __________ come to the party if he finishes his work early.
8. __________ you please turn down the music?
9. You __________ have told me earlier: I was worried.
10. He is a genius: he __________ solve this problem easily.
11. __________ I help you carry those bags?
12. She __________ not be at home: her car is not outside.
13. You __________ respect your parents and teachers.
14. We __________ try a different approach to this problem.
15. __________ you like some tea or coffee?

Answers:

1. should / must
2. May / Can / Could
3. could
4. might / may
5. Shall
6. must
7. might / may / will
8. Could / Would / Will
9. should
10. can / must
11. Shall / Can
12. must
13. should / ought to / must
14. should / could / might
15. Would

C. Each of the following sentences contains one error related to modal auxiliaries. Find and correct the error.

1. She cans speak English very well.
2. You must to finish your homework before watching television.
3. Does he can drive a car?
4. She will can join us next week.
5. You must not bring food: it will be provided for free.
6. He might be exhausted after running for ten hours: he needs rest.
7. May you please help me with this question?
8. If she will work hard, she would get good marks.
9. You should not to speak during the examination.
10. They dare not to enter the principal’s office without permission.

Answers:

1. ‘cans’ → can (modal auxiliaries do not add -s)
2. ‘must to finish’ → must finish (no ‘to’ after pure modals)
3. ‘Does he can drive’ → Can he drive (no ‘do’ with modal auxiliaries)
4. ‘will can’ → will be able to (two modals cannot be used together)
5. ‘must not’ → need not (the meaning is ‘not necessary’, not ‘prohibited’)
6. ‘might be’ → must be (logical certainty based on evidence)
7. ‘May you’ → Could/Would you (‘may’ is not typically used for polite requests)
8. ‘will work’ → works / ‘she would’ → she will (first conditional: If she works hard, she will get good marks.)
9. ‘should not to speak’ → should not speak (no ‘to’ after modal auxiliaries)
10. ‘dare not to enter’ → dare not enter (no ‘to’ when ‘dare’ functions as a modal)

D. Choose the correct modal auxiliary from the options given to complete each sentence.

1. You __________ (must / should / might) wear a helmet while riding a bike: it is the law.
2. She __________ (could / would / shall) be at the library: I am not sure.
3. __________ (Will / Shall / Would) I carry your bag for you?
4. He __________ (could / must / should) have informed us about the change in plans earlier.
5. __________ (Can / May / Shall) I speak to the manager, please? (formal)
6. They __________ (will / would / could) arrive by six if the traffic is good.
7. You __________ (must not / need not / should not) bring a gift: your presence is enough.
8. When she was younger, she __________ (can / could / might) dance beautifully.
9. __________ (Would / Could / Shall) you like to join us for dinner this evening?
10. Students __________ (shall / should / will) submit their project files by the end of this week.

Answers:

1. must
2. could / might
3. Shall
4. should
5. May
6. will / could
7. need not
8. could
9. Would
10. shall / must / should

E. Rewrite each sentence using the modal auxiliary in brackets, making necessary changes.

1. It is possible that she is at the office. (may)
2. I advise you to see a doctor. (should)
3. He had the ability to play chess when he was six. (could)
4. It is necessary for you to submit the form today. (must)
5. It is permitted for me to use the lab after hours? (may)
6. It is probable that they will arrive late. (might)
7. I am willing to help you with the project. (will)
8. It was his habit to read for one hour every evening. (would)
9. It is morally right for you to apologise. (ought to)
10. It is not necessary for her to attend the meeting. (need not)

Answers:

1. She may be at the office.
2. You should see a doctor.
3. He could play chess when he was six.
4. You must submit the form today.
5. May I use the lab after hours?
6. They might arrive late.
7. I will help you with the project.
8. He would read for one hour every evening.
9. You ought to apologise.
10. She need not attend the meeting.