143 Ought/should with the perfect infinitive

This construction is used to express an unfulfilled obligation or a sensible action that was neglected. In the negative it expresses a wrong or foolish action in the past.

You ought to have told him that the paint on that seat was wet.

You should have turned his omelette; he likes it turned.

They ought to have stopped at the traffic lights.

She shouldn't have opened the letter; it wasn 't addressed to her.

The Emergency Exit doors shouldn't have been blocked.

144 Must and have to: forms

A must

must is a modal verb (see 107 B). It is used in the present or future.

Negative: must not/mustn't

Interrogative: must I? etc.

Negative interrogative: must I not/mustn't I? etc.

The past tense is supplied by had to.

must takes the bare infinitive.

It can express obligation and emphatic advice:

father: You must get up earlier in the morning, (obligation) You must take more exercise. Join a squash club, (advice)

B have to

Obligation		No obligation
Speaker's authority	External authority
Future must	shall/will have to	shan 't/won 't have to
Present must	have to * have (got) to*	don't/doesn't have to* haven't (got) to*
Past had to	had to	didn 't have to hadn 't (got) to

C Difference between the starred have to forms

have to (without got) and its negative don't/doesn't have to are the correct forms for habitual actions but can be used for single actions also, and are common in American English. have (got) to and haven't (got) to are for single actions only

TOM: / have to go to work every day except Sunday. But I don 7 have to work a full day on Saturday. But on Sunday he could say:

I'm glad I haven't (got) to go to work today or I'm glad I don't have to go to work today

In the past didn't have to can be used for both habitual and single actions in the past.

hadn't (got) to is used more for single actions. didn't have to is the more generally used form. have to in the affirmative expresses obligation. have to in the negative expresses absence of obligation. This can also be expressed by need not, don't need etc. (see 149).

145 Difference between must and have to in the affirmative

A must expresses obligation imposed by the speaker:

MOTHER: You must wipe your feet when you come in. have to expresses external obligation:

small Ben : / have to tape my feet every time I come in. B Second person examples

1 Speaker's authority

MOTHER: You must wear a dress tonight. You can't go to the opera

in those dreadful jeans

EMPLOYER: You must use a dictionary. I'm tired of correcting your

spelling mistakes.

DOCTOR: You must cut down on your smoking,

2 External authority

You have to wear uniform on duty, don't you? You have to train very hard for these big matches, I suppose You 'II have to get up earlier when you start work, won't you ?

You'll have to cross the line by the footbridge.

C Third person examples

Here must is chiefly used in written orders or instructions:

R AILWAY 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 then desks by 9 00.

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

They'll have to send a diver down to examine the hull.

Tf we used must instead of have to above it might imply that the peaker 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 First person examples

In the first person the difference between must and have to is less important and very often either form is possible:

TYPIST: / must/will have to buy a dictionary.

PATIENT: / must/have to/will have to cut down on my smoking But have to is better for habits:

/ 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 a dream I had last night.

Before we do anything I must find my cheque book.

E Some other examples (all persons)

You must come and see us some time. (This is quite a usual way of

expressing a casual invitation.)

The children have to play in the street till their parents come home.

This sort of thing must stop! (The speaker either has authority or

feels very strongly about it.)

You must write to your uncle and thank him for his nice present.

If there are no taxis we'll have to walk.

If your father was a poor man you'd have to work.

We have to walk our dog twice a day.

NOTICE IN shop WINDOW Closing down sale! Everything must go!

F Affirmative obligations 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:

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

You had to pay duty on that, I suppose?

There were no buses so he had to walk.