ESL CONNECT | Modal Verbs of Obligation

Explanation: modal verbs of obligation

Use modal verbs and semi-modal structures to talk about rules, duties, necessity, advice and prohibition.

1. Must

Use must + base verb for strong obligation. It often feels personal, urgent or very important.

Form	Example	Meaning
must + base verb	You must wear a seatbelt.	It is necessary / it is a rule.
must + base verb	I must call my doctor.	I feel this is very important.

2. Have to

Use have to / has to + base verb for rules, duties and external obligations.

Subject	Affirmative	Negative	Question
I / you / we / they	I have to study.	I don’t have to study.	Do you have to study?
he / she / it	She has to work.	She doesn’t have to work.	Does she have to work?

3. Need to

Use need to + base verb for necessity. It is usually less strong than must.

Examples:
I need to finish my homework.
She needs to practise more.
We don’t need to leave yet.

4. Should

Use should + base verb for advice or a good idea. It is not as strong as must or have to.

Examples:
You should drink more water.
He shouldn’t eat so much sugar.
Should I call her?

5. Mustn’t vs don’t have to

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

Form	Meaning	Example
mustn’t	prohibition / not allowed	You mustn’t smoke here.
don’t have to	no obligation / not necessary	You don’t have to come if you’re tired.

6. Past obligation

Use had to + base verb for obligation in the past.

Present	Past
I have to work today.	I had to work yesterday.
She has to wear a uniform.	She had to wear a uniform at school.
We don’t have to pay today.	We didn’t have to pay yesterday.

Remember:
Strong obligation/rule: must / have to
Necessity: need to
Advice: should
Prohibition: mustn’t
No obligation: don’t have to
Past obligation: had to

Must and have to

Choose the correct obligation form.

1. You __________ a helmet on this construction site.

must wear must to wear must wearing

2. She __________ late tonight.

have to work has to work has work

3. We __________ before 8:30.

have to arrive has to arrive have arrive

4. __________ wear a uniform at school?

Do you have to Have you to Must you to

Write the sentence

Complete: I / have to / study / tonight.

Answer: I have to study tonight.

Need to

Choose the correct necessity form.

1. I __________ this report today.

need finish need to finish need finishing

2. He __________ more before the exam.

need to practise needs to practise needs practise

3. We __________ leave yet. It’s still early.

don’t need to mustn’t needn’t to

4. __________ bring her passport?

Does she need to Does she needs to Need she to

Should for advice

Choose the correct advice form.

1. You look tired. You __________ some water.

should to drink should drink should drinking

2. He __________ so much fast food.

shouldn’t eat doesn’t should eat shouldn’t to eat

3. __________ the doctor?

Do I should call Should I call Should I to call

4. If you want to improve, you __________ every day.

should study mustn’t study don’t have to study

Write the sentence

Give advice: You / should / go to bed / earlier.

Answer: You should go to bed earlier.

Mustn’t vs don’t have to

Choose carefully: prohibition or no obligation?

1. You __________ smoke in the hospital. It is forbidden.

don’t have to mustn’t should

2. You __________ come to the meeting if you’re busy. It’s optional.

mustn’t don’t have to must

3. Students __________ use phones during the exam.

mustn’t don’t have to need to

4. She __________ wear a uniform at her new school.

mustn’t doesn’t have to don’t have to

Past obligation: had to

Use had to for obligation in the past.

1. Yesterday, I __________ late.

have to work had to work must worked

2. She __________ for the test last night.

has to study had to study had study

3. We __________ for the tickets. They were free.

didn’t have to pay mustn’t pay didn’t had to pay

4. __________ wake up early yesterday?

Did you have to Had you to Did you had to

B1 contrast practice

Choose the best meaning: rule, advice, no obligation, prohibition or past obligation.

1. You __________ show your passport at airport security. It’s required.

should must don’t have to

2. You __________ revise before the exam. It’s a good idea.

mustn’t should don’t have to

3. You __________ park here. It’s illegal.

don’t have to mustn’t need to

4. You __________ bring food. There will be a buffet.

mustn’t don’t have to must

5. Last week, we __________ finish the project in one day.

have to had to must to

Correct the mistake

Correct: She have to wear a uniform.

Answer: She has to wear a uniform.

Correct: You don’t have to use your phone in the exam. It is forbidden.

Answer: You mustn’t use your phone in the exam.

Mixed practice

Choose the best answer.

1. I __________ charge my phone. The battery is low.

mustn’t need to don’t have to

2. You __________ touch that machine. It’s dangerous.

mustn’t don’t have to should

3. He __________ work tomorrow. It’s his day off.

doesn’t have to mustn’t don’t have to

4. You __________ go to bed so late every night.

mustn’t shouldn’t don’t have to

5. Yesterday, I __________ wait for two hours.

have to had to must wait

Final writing practice

1. Write one school or workplace rule with must or have to.

2. Write one prohibition with mustn’t.

3. Write one sentence with don’t have to.

4. Write one advice sentence with should.