Present prohibition failure to observe a prohibition

You can't park here You shouldn t have parked there

You mustn't park here You ought not to have parked there

For shouldn't ) and ought(n't) to in indirect speech [> 15.13n6]

Shouldn't have and oughtn't to have are not ambiguous in the way that should

have and ought to have can sometimes be ambiguous [compare > 11.29n1 ]

For the use of must(n't) in indirect speech [> 15.13n6]

Have to can replace must in the present [> 11.48, 11.50] but don't/didn't have

to cannot replace mustn't in the present and past [> 11.55, 11.57.1 ]

1.53 Lack of necessity: 'needn't/don't have to/haven't got to'

Lack of necessity can be expressed by needn t don t have to and the more informal haven t got to (where got is often stressed)

You needn't

You don't have to work such long hours

You haven't got to

(i e you can work fewer hours, if you choose to)

The above forms can be used to express the subjective point of view of the speaker that the listener has a choice or has permission not to do something Note that (You) haven t to is a regional BrE variation of (You) don t have to

11.54 Inadvisability —> prohibition: 'a scale of choice'

We can use modals and other verbs to express inadvisability —> prohibition on a scale which reflects a degree of choice This scale may vary according to the subjective view of the speaker This is particularly the case when we are addressing others directly with you, or when we are referring to others with he she, and they At one end of the scale (see next page) the advice (however strong) can be ignored At the other end of the scale, the prohibition is total and, in the speaker's opinion, there is no choice at all

11 Modal auxiliaries and related verbs

inadvisability shouldn't generally means 'in my opinion, it is

inadvisable to/it is (your) duty not to'
oughtn t to can be slightly stronger than

shouldn t It is sometimes used to refer to regulations and duties imposed from the outside You oughtn t to park so near the crossing suggests 'it's your public duty not to do this' had better not is stronger than shouldn t and

oughtn t 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 not overtake here am/is/are not to can be used for instructions [> 9.48.1 ]

can't is nearly as strong as mustn't to

suggest something is prohibited You can t park here

prohibition mustn t conveys absolute prohibition In

the opinion of the speaker, there is no choice at all This opinion may be subjective or may be supported by some outside authority as in You mustn t turn left (e g there's a road sign forbidding it)

11.55 'Mustn't', 'needn't', 'don't have to', 'haven't got to'

Though must have to and have got to are generally interchangeable in the affirmative [> 11.48], don't have to and haven't got to can never replace mustn t to convey prohibition Like needn t they convey lack of necessity [> 11.56.1]

Mustn t conveys the strongest possible opinion of the speaker

You really mustn't say things like that in front of your mother

Julian mustn't hitchhike to Turkey on his own Prohibition reflecting external authority (in e g public notices, documents) is often expressed as must not (in full)

Life belts must not be removed

Candidates must not attempt more than four questions

Haven't got to should be avoided with adverbs of frequency (always sometimes, etc) for reasons of style So

I needn't always be at tne office by 9