Modal Verbs: Can, Could, May, Might, Must & Should

In this lesson, you will learn the rules, structures, meanings, differences,
examples, common mistakes, and typical uses of the most important English modal verbs.
At the end, you can practice with exercises and a short grammar quiz.

What Are Modal Verbs?

Modal verbs are auxiliary verbs that come before the main verb.
They add meanings such as possibility, ability, advice, permission,
or obligation.

Basic structure:

Subject + modal verb + base verb

• I can swim.
• She might come.
• You should study.
• They must leave.

Important Modal Verb Rule

After most modal verbs, we use the
base form of the verb without “to”.

✅ She can swim.

❌ She can to swim.

✅ You should study.

❌ You should to study.

The main modal verbs also do not change according to the subject.

• I can swim.
• He can swim.
• She can swim.
• They can swim.

We do not add -s after a modal verb.

❌ He cans swim.

✅ He can swim.

Main English Modal Verbs

• Can: ability, permission, possibility
• Could: past ability, polite requests, possibility
• May: permission and possibility
• Might: weaker possibility
• Must: strong obligation, necessity, deduction
• Should: advice, recommendation, expectation

Can

Can is one of the most common modal verbs in English.
It is mainly used for ability, permission, and possibility.

1. Ability

• I can swim.
• She can speak three languages.
• He can drive a truck.
• They can play the piano.

2. Permission

• Can I use your phone?
• Can we leave early?
• You can sit here.

3. Requests

• Can you help me?
• Can you open the window?
• Can you send me the document?

4. General Possibility

• Driving in winter can be dangerous.
• This job can be stressful.
• English grammar can be difficult at first.

Cannot and Can’t

The negative form of can is
cannot or can’t.

• I can’t swim.
• She cannot come today.
• We can’t park here.

Could

Could has several important uses.
It can describe past ability, polite requests, suggestions,
and possibility.

1. Past Ability

• I could swim when I was five.
• She could speak French when she was younger.
• He could run very fast as a child.

2. Polite Requests

Could is often more polite than can.

• Could you help me?
• Could you open the door, please?
• Could you explain this question?

3. Possibility

• It could rain later.
• That could be the answer.
• They could arrive tonight.

4. Suggestions

• We could go to the cinema tonight.
• You could try restarting the computer.
• They could take the train instead.

Can vs Could

Both can and could can express ability,
but they usually refer to different times.

Present ability:
I can swim.

Past ability:
I could swim when I was five.

For requests, could generally sounds more polite.

Can you help me?

Could you help me?

Both are correct, but the second is usually more polite.

May

May is commonly used for possibility
and formal permission.

1. Possibility

• It may rain tomorrow.
• She may come to the meeting.
• The train may be late.
• Prices may increase next year.

2. Formal Permission

• May I come in?
• May I ask a question?
• May I use your phone?

May I…? is generally more formal than
Can I…?

Might

Might is mainly used to express possibility,
especially when the speaker is uncertain.

• It might rain tonight.
• She might come later.
• They might cancel the meeting.
• I might buy a new laptop next month.

May vs Might

Both may and might can express possibility.
In many situations, both are possible.

It may rain later.

It might rain later.

In everyday English, might can sometimes suggest
slightly more uncertainty, although the difference is often small.

Can vs May for Permission

Both forms can be used when asking for permission.

Can I leave early?

This is common and natural in everyday English.

May I leave early?

This sounds more formal.

Must

Must is mainly used for strong obligation,
necessity, and logical conclusions.

1. Strong Obligation

• You must wear a seat belt.
• Students must submit the assignment by Friday.
• You must follow the safety rules.
• Employees must wear identification cards.

2. Strong Personal Necessity

• I must remember to call her.
• I must finish this report today.
• We must leave soon.

3. Logical Deduction

We can use must when we are almost certain
something is true based on evidence.

The lights are on. Someone must be home.

She studied all night. She must be tired.

He’s wearing a uniform. He must work here.

Must Not vs Don’t Have To

This is an important distinction.

Must Not / Mustn’t

Mustn’t means something is prohibited.

• You mustn’t smoke here.
• You mustn’t touch that machine.
• Students mustn’t use phones during the exam.

Don’t Have To

Don’t have to means something is not necessary.

• You don’t have to come tomorrow.
• We don’t have to wear uniforms.
• She doesn’t have to work today.

Compare:

You mustn’t park here.
Parking is prohibited.

You don’t have to park here.
There is no necessity to park here.

Must vs Have To

Both must and have to
can express obligation.

You must finish the report.

You have to finish the report.

In many situations, the meaning is similar.
However, must often sounds like a strong rule,
instruction, or personal necessity, while have to
is commonly used for external rules or circumstances.

Examples

• I must remember to call my mother.
• I have to wear a uniform at work.
• You must be careful.
• Employees have to arrive before 9 a.m.

Should

Should is mainly used for advice,
recommendations, expectations, and mild obligation.

1. Advice

• You should study more.
• You should see a doctor.
• She should get more sleep.
• They should leave early.

2. Recommendations

• You should visit London.
• You should try this restaurant.
• We should take the train.

3. Expectation

Should can show that we expect something to happen.

• The train should arrive soon.
• She should be home by 7 p.m.
• The package should arrive tomorrow.

Should Not / Shouldn’t

Shouldn’t is used to give negative advice.

• You shouldn’t smoke.
• You shouldn’t drive so fast.
• He shouldn’t stay up so late.
• They shouldn’t spend so much money.

Must vs Should

The main difference is the strength of the obligation or advice.

Must = Strong Obligation

You must wear a helmet.

This sounds like a rule or strong requirement.

Should = Advice

You should wear a helmet.

This sounds like a recommendation.

Must vs Should Examples

• You must show your passport at immigration.
• You should arrive at the airport early.
• Students must follow the exam rules.
• Students should revise before the exam.

Modals of Possibility

Several modal verbs can express different levels of possibility.

• may: possible
• might: possible, often slightly less certain
• could: possible

Examples:

• She may come tonight.
• She might come tonight.
• She could come tonight.

All three sentences suggest that her arrival is possible,
but not certain.

Modals of Deduction

Modal verbs can also show how certain we are about a situation.

Must = Strong Certainty

He has been working for twelve hours. He must be exhausted.

Might / May / Could = Possibility

She might be at work.

She may be at work.

She could be at work.

Can’t = Strong Impossibility

He can’t be at home. I just saw him at the office.

Modal Verbs in Negative Sentences

• can → cannot / can’t
• could → could not / couldn’t
• may → may not
• might → might not
• must → must not / mustn’t
• should → should not / shouldn’t

Examples:

• I can’t drive.
• She couldn’t come yesterday.
• It may not rain.
• They might not attend.
• You mustn’t enter this room.
• You shouldn’t worry.

Questions with Modal Verbs

To form questions, put the modal verb before the subject.

Modal + Subject + Base Verb?

• Can you swim?
• Could you help me?
• May I come in?
• Should we leave now?

We do not normally use do or does
with modal verbs.

❌ Do you can swim?

✅ Can you swim?

Modal Verbs Quick Comparison

Common Modal Verb Mistakes

Mistake 1: Using “To” After a Modal

❌ I can to swim.

✅ I can swim.

Mistake 2: Adding -s with He or She

❌ She cans drive.

✅ She can drive.

Mistake 3: Using Do or Does in Questions

❌ Do you can help me?

✅ Can you help me?

Mistake 4: Using the Wrong Negative Meaning

❌ You mustn’t come tomorrow if you don’t want to.

If attendance is optional, say:

✅ You don’t have to come tomorrow.

Mistake 5: Confusing Must and Should

You must see a doctor.

This sounds like a strong necessity.

You should see a doctor.

This gives advice.

Mistake 6: Using a Past Verb After a Modal

❌ She can went home.

✅ She can go home.

Modal Verb Examples

• I can speak English.
• Could you help me with this question?
• It may rain tomorrow.
• She might arrive late.
• You must wear a seat belt.
• You should drink more water.
• We can’t park here.
• They couldn’t attend the meeting.
• Students mustn’t use phones during the test.
• You shouldn’t stay up so late.
• He must be tired after working all day.
• She might be at home.

Modal Verbs Worksheet

Choose the most appropriate modal verb:
can, could, may, might, must, or should.

1. You ________ wear a seat belt while driving.
2. When I was six, I ________ swim very well.
3. ________ you help me with this bag, please?
4. It ________ rain later, so take an umbrella.
5. You look tired. You ________ get some rest.
6. She speaks four languages. She ________ speak French very well.
7. Students ________ use their phones during the exam.
8. ________ I ask you a question?
9. The lights are on. Someone ________ be inside.
10. We ________ go to the cinema tonight, but we haven’t decided yet.

Modal Verbs Mini Quiz

1. She _____ speak three languages.

A) can
B) cans
C) can to

2. When I was a child, I _____ run very fast.

A) can
B) could
C) should

3. You have a high fever. You _____ see a doctor.

A) should
B) might
C) can be

4. Students _____ cheat in an exam.

A) don’t have to
B) mustn’t
C) might

5. “May I come in?” expresses:

A) ability
B) permission
C) past ability

6. The lights are on. They _____ be at home.

A) must
B) shouldn’t
C) couldn’t

7. Which sentence is correct?

A) She can to drive.
B) She cans drive.
C) She can drive.

8. “You don’t have to come tomorrow” means:

A) Coming is prohibited.
B) Coming is not necessary.
C) You must come.

9. Which modal is commonly used for advice?

A) should
B) may
C) can

10. “It might rain tonight” expresses:

A) certainty
B) possibility
C) obligation

Modal Verbs Summary

Modal verbs help us express ability, possibility, permission,
obligation, advice, and certainty.

• Can: ability and permission
• Could: past ability and polite requests
• May: possibility and formal permission
• Might: possibility and uncertainty
• Must: strong obligation and deduction
• Should: advice and recommendation

Remember the basic rule:

Modal verb + base form of the main verb

✅ She can speak English.

✅ You should study.

✅ They might come later.

Frequently Asked Questions

What are modal verbs in English?

Modal verbs are auxiliary verbs that express meanings such as
ability, permission, possibility, obligation, advice, and certainty.

What are the most common modal verbs?

Common modal verbs include
can, could, may, might, must, should, will, would, and shall.

Do we use “to” after modal verbs?

Normally, no. Use the base verb directly after the modal.

✅ She can swim.

❌ She can to swim.

What is the difference between can and could?

Can commonly expresses present ability,
while could can express past ability,
possibility, or a more polite request.

What is the difference between may and might?

Both express possibility. Might can sometimes suggest
a slightly lower level of certainty, although they are often interchangeable.

What is the difference between must and should?

Must expresses strong obligation or necessity,
while should usually expresses advice or recommendation.

What is the difference between mustn’t and don’t have to?

Mustn’t means something is prohibited.
Don’t have to means something is not necessary.

Continue Practicing English Grammar

Improve your knowledge of modal verbs with these related
English Test Center tests and grammar exercises:

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  Modal Verbs: Must / Have To / Should – B1 Grammar Test
  
• 
  Modals: Should / Must / Have To / Might – B1 Grammar Test
  
• 
  Modals of Deduction & Speculation – B2 Grammar Test
  
• 
  Advanced Modals – C1 Grammar Test
  
• 
  Conditionals: Zero, First, Second & Third
  
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  Browse All English Grammar Worksheets
  
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  English Grammar Exercises
  

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