Obligation and necessity: must/have to/need (to)

MUST is used:

1) to express total obligation (the authority comes from the speaker)

I really must get a driving license.

Must we pay extra?

You must be home by 10 o'clock.

2) to express necessity

You must phone home at once.

I’ve got a terrible pain in my back. I must go and see the doctor.

3) to express prohibition

You mustn't be late for classes.

4) in public notices, etc.

All visitors must report to the duty officer.

Exercise 9. Rewrite the following sentences as positive, negative or a question according to the instructions.

Example: We mustn't tell him about the accident. (positive)

We must tell him about the accident.

I must fix the switch myself. (negative)

I mustn't fix the switch myself.

We must take part in the discussion. (question)

Must we take part in the discussion?

1. If a traffic light is red, a car mustn't stop. (positive)

2. He must work overtime every day. (negative)

3. You mustn't be at the airport an hour and a half before the departure of the plane. (positive)

4. You must wear a helmet when you drive a motorbike. (question)

5. Children must play with matches. (negative)

HAVE (GOT) TO is used:

1) to express obligation (the authority comes from outside the speaker)

I've (got) to be home by 10 o'clock. (My parents insist.)

We have to drive on the left in Britain. (That is the law.)

2) to express necessity

I have (got) to go and see the doctor at 9 o'clock.

NOTE:

a) Have to is not a modal verb but it often has the same meaning as must, and is used instead of must in some tenses. It forms questions and negatives in the same way as all other main verbs. We use do/does in the present, did/didn't in the past and will in the future.

I/You/We/They don't have to hurry. There's plenty of time.

He /She doesn't have to wear smart clothes to work.

What time did you have to start work yesterday?

Does he have to attend the meeting?

Jack will have to buy a new car soon.

It's Sunday tomorrow so I won't have to go to the institute.

b) We normally use have to not have got to, for things that happen repeatedly, especially with adverbs of frequency.

I always have to work late on Wednesday evenings.

I've got to work late this evening.

Do you often have to get up early?

Have you got to get up early tomorrow?

c) We often use have got to instead of have to to talk about obligation and necessity.

Have got to is more informal.

Have got is mostly used in the present.

I've got to stop smoking.

They had to go to Kiev for a conference.

Exercise 10. Rewrite the following sentences as positive, negative or a general question. Use have got where possible.

Example: You leave.

You've got to leave.

You haven't got to leave.

Have you got to leave?

1. At twelve o'clock they’ll lock the door.

2. Laura do her homework every day.

3. I pay in cash for this purchase.

4. Most schoolchildren wear a uniform.

Must vs. Have (got) to

Meaning	Must	Have (got) to
Obligation & necessity	1. You must leave. = You can’t stay. (The authority comes from the speaker.)	1. You’ve got to leave. = You can’t stay. (The authority comes from outside the speaker.)
	2. You mustn't leave. = You can't go. — obligation	2. You don't have to leave. = You can go or stay, as you like. — no obligation
Prohibition	You mustn't smoke here.

Exercise 11. Complete the sentences with have (got) to or must.

Use the negative or question if necessary. Put have to in the correct tense.