11. Must and have to: forms

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Obligation No obligation

Speaker’s External

authority authority

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Future must shall/will have to shan’t/won’t have to

Present must have to don’t/doesn’t have to

have (got) to haven’t (got) to

Past had to had to didn’t have to

hadn’t (got) to

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must is used in the present and future.

Negative: must not

Interrogative: must I?

The past tense is supplied by had to.

must takes the bare infinitive.

It can express obligation and emphatic advice.

Boss: You must finish this work before you leave(obligation)

You must go and see this play. It’s so much spoken about ( emphatic advice).

12. Difference between have to and have got to Forms

The grammar is quite similar to the use of have and have got to talk about states. The main points are as follows:

A. In British English, we make a distinction between habitual or repeated obligation and non-habitual obligation. When there is the idea of repetition, we use ordinary verb-forms, with do in questions and negatives.

I don’t usually have to work on Sundays.

Do you have to wear uniform at work?

B. When we are talking about one thing that we are obliged to do, it is more usual to use got-forms (particularly in informal English).

I haven’t got to work tomorrow.

Have you got to do interpreting next week?

C. Got-forms are unusual in the past, and are replaced by ordinary verb-forms.

Did you have to go to church on Sundays?

13. Difference between must and have to in the Affirmative

A. Both these verbs are used to talk about obligation. Their meaning is not quite the same. Must is most often used to talk about an obligation that depends on the person speaking or listening: If I say that you or I must do something, I probably mean that I feel it is necessary. Have (got) to is generally used to talk about obligations that come from ‘outside’. If I say that somebody has to do something, I probably mean that another person wants it done, or that there is a law, a rule, an agreement, or something of the kind.

Compare:

I must stop smoking. (I want to.)

You must try to get to work on time. (I want you to.)

I must make an appointment with the dentist. (I’ve got toothache.)

This is an awful party - we really must go. (I want us to go.)

You’ve got to go and see the boss. (He wants you to.)

Catholics have to go to church on Sundays. (Their religion tells them to.)

I’ve got to see the dentist tomorrow. (I have an appointment.)

This is a lovely party, but we’ve got to go because of the baby-sitter.

B. In the second person we use must to express the speaker’s authority:

Mother: You must put on a sweater. It’s cold today.

Employer: You must use a dictionary. I’m tired of correcting your spelling mistakes.

Doctor: You must cut down on your smoking.

but we use have to to express external authority:

You have to wear uniform on duty.

You have to train very hard for these big matches.

You’ll have to get up earlier when you start work, won’t you?

C. In the third person must is chiefly used in written orders or instructions:

Railway company: Passengers must cross the line by the footbridge.

Office Manager: Staff must be at their desks by 9.00.

Regulation: A trailer must have two rear lamps.

When we are merely stating or commenting on another person’s obligations we use have to:

In this office even the senior staff have to be at their desks by 9.00.

She has to make her children’s clothes. She can’t afford to buy them.

If we used must instead of have to above it might imply that the speaker had authority to order these actions.

But must may be used when the speaker approves of an obligation:

A driver who has knocked someone down must stop.

(The speaker thinks it is the driver’s duty to stop.)

Or when the speaker feels strongly:

Something must be done to stop these accidents.

D. In the first person the difference between must and have to is less important and very often either form is possible. But have to is better for habits:

I have to take two of these pills a day.

and must is better when the obligations are urgent or seem important to the speaker:

I must tell you about the dream I had last night.

Before we do anything I must find my cheque book.

E. Affirmative obligation in the past: had to

Here the distinction between the speaker’s authority and external authority cannot be expressed and there is only one form, had to:

I ran out of money and had to borrow from Tom.

You had to pay duty on that, I suppose?