Present inescapable obligation past inescapable obligation

/ must stop smoking I had to stop smoking

(I am obliged to stop smoking (I was obliged to stop smoking

and I shall it is my duty) and I did it was my duty )

For should and ought to in indirect speech [> 15.13n 6]

For the ambiguity of should have and ought to have [> 11.29n1 ]

For the uses of must and had to in indirect speech [15.13n6]


11 Modal auxiliaries and related verbs

11.47 Advisability —> necessity: 'a scale of choice'

We can use modals and other verbs to express advisability on a scale

which reflects a degree of choice. This scale may vary according to

the subjective point of view of the speaker.

advisabilityshould: generally means 'in my opinion, it is

advisable to1 or 'it is (your) duty'.
ought to: can be slightly stronger than should in

that it is sometimes used to refer to
regulations or duties imposed from the
outside: You ought to vote (= it is your
public duty). Should is more likely than
ought to in questions and negatives.
had better: is stronger than should and ought to.
It is used to recommend future action on
a particular occasion, not in general.
It carries a hint of threat, warning or
urgency: You'd better see a doctor,
am/is/are to:
can be used for instructions [compare
> 9.48.1]: You're to report for duty at 7
need (to):
(= it is necessary to).

have to: is an alternative to musf and fills the

gaps in that defective verb [> 11.4], have got to: like have to, but more informal.

necessitymust: like have to and have got to, suggests

inescapable obligation. In the speaker's opinion there is no choice at all.

11.48 'Must', 'have to' and 'have got to'

As far as meaning is concerned, these three forms are largely interchangeable. However, there are differences between them. When used in the first person, have to and have got to (often pronounced / haevta/ and /hav'gDta/ in everyday speech) can refer to an external authority and might be preferable to must in: e.g. We have to/We've got to send these VAT forms back before the end of the month (i.e. we are required to do so by law)

On the other hand, must can express a speaker's authority over himself and might be preferable to have to/have got to in: I/We really mustdo something about the weeds in this garden (i.e. but I don't have to account to anybody if I don't)

In other persons {you, etc.) must conveys more strongly than have to the idea of inescapable obligation or urgency in: e.g. You must phone home at once It's urgent

Have to and have got to are interchangeable for single actions: / have to/have got to check the oil level in the car.

However they are not always interchangeable when we refer to

habitual actions. The following are possible:

/ have to/I have got to leave home every morning at 7 30


Advisability, duty/obligation and necessity

But when one-word adverbs of frequency (always, sometimes, etc.)

are used have to is always preferable to have got to:

I often have to get up at 5 Do you ever have toget upat 5?

Must (not have to or have got to) is used in public notices or

documents expressing commands:

Cyclists mustdismount Candidates mustchoose five questions

We generally prefer Must you. ? to Do you have to ?/Have you got

to ? to mean 'Can't you stop yourself...?'

Must you always interrupt me when I'm speaking?

Must is also used in pressing invitations, such as:

You really must come and see us some time and in emphatic advice, such as:

You really must take a holiday this year Even when heavily stressed, these uses of must do not mean or imply 'inescapable obligation'.