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Concourse 2

Expressing obligation (or its lack), advice and permission

keep out

Expressing obligation is a key communicative language skill and needed by learners at all levels of competence.  The essential concept to get clear is that this concerns deontic modality (from the Greek deont-, that which is obligatory) and not epistemic modality which concerns the truth or otherwise of a proposition.
To be clear:

  • That must be the right train
  • She should be at home by now
  • That ought to be the street
  • There's an outside chance he's the manager
  • I am convinced that's wrong
  • I suspect that's the problem here
  • are all examples of epistemic modality, expressing the speaker's view of the likelihood of something being true but
  • You must get off here
  • You should write to your father
  • He ought to speak less abruptly
  • There's some need to wait a while
  • I am forbidden from doing that
  • I advise against it
  • are all examples of deontic modality expressing some kind of obligation or duty.

You will see that modal expressions, including modal verbs are often used to express both types of modality in a similar way and that can confuse the issue, especially for learners.
For more on epistemic modality, see the guide to expressing (un)certainty.

An associated idea is directive modality (e.g., Keep out!, Don't say that! etc.) but we shall consider that here under the general heading.  For teaching purposes, the distinction is not needed.
This area is normally taught in a way that confines it to the use of modal auxiliary verbs.  That is both misleading and unnecessarily constricting, as we shall see.

don't forget

A word on and of advice

Don't forget your hat!  

In the classroom, advice and obligation are often handled separately and there's some sense in that.  However, the borderline between advice and obligation is blurred to the point of invisibility.  It almost always depends on role relationships.  For example:

Expressions Roles Function
You should do it before Thursday Boss to employee Obligation
Friend to friend Advice
You shouldn't smoke Friend to friend Advice
Doctor to patient Obligation
You oughtn't to speak to her like that Teacher to pupil Obligation
Pupil to pupil Advice
This is a bit urgent Chef to kitchen worker Obligation
Wife to husband Advice
and so on.

In this guide, we shall not be distinguishing between advice and obligation but you should bear the role of power relationships in mind.


Two forms of deontic modality

Much is made of a distinction in the type of obligation expressed:

  1. Obligation from within
    1. This is known as intrinsic obligation and concerns personal feelings of obligation (i.e., duty or personal goal fulfilment)
      Examples are:
          I should write to thank her
          I feel obliged to pay you back
  2. Obligation from without
    1. This is referred to as extrinsic obligation and concerns that which one is obliged by external forces to do (even if one feels no personal obligation)
      Examples are:
          You must get a visa for the USA
          It is necessary to buy a ticket before travelling

It is sometimes suggested that these two types of obligation have wholly different exponents in English (e.g., the famous have to vs. must and ought to vs. should distinctions) and that the difference leads to a hard-and-fast rule concerning which form(s) to use.  That's not entirely true.


The three-way switch

It is also often assumed that there are only three main types of obligation, to wit:

  1. Obligation to do something: You must come on time
  2. Obligation not to do something: You must not be late
  3. Lack of any obligation: You don't have to come on time

This can also mislead because, just as there are degrees of certainty and degrees of politeness, there are also degrees of obligation:

  1. Strong obligation to do something: Come on time!
    Weak obligation to do something: You are advised to come on time
  2. Strong obligation not to do something: Don't be late!
    Weak obligation not to do something: Please try not to be late
  3. Total lack of obligation: It doesn't matter when you come
    Some mild preference: It would be nice if you came on time but ...

And, of course, there are subtle gradations between the strongest and weakest forms of obligation.


Expressing obligation

Here are some examples of what this guide is about.
Can you spot:

  1. The parts of the following in which the speakers / writers are expressing an obligation (or its lack) or a duty?
  2. The way they are doing it – i.e., the linguistic realisation of deontic modality?
  3. What type of obligation, intrinsic or extrinsic, is being expressed?

When you have an answer to a., b and c. above, click on the eye open to reveal some comment.

It seems necessary.
It appears obligatory.
eye open
  1. It seems necessary to get some kind of permission.
  2. The use of copular verbs such as seem, appear, be etc. is a common strategy to introduce some kind of obligation.
  3. Expressions like this cannot often be used for personal, intrinsic, obligations.
Stop that!
Go on!
Please refrain from smoking.
eye open
  1. Stop that!
    Go on!
    Please refrain from smoking.
  2. The use of the imperative is not necessarily as direct or abrupt in English as it can be in many languages (and therefore avoided in adult-to-adult interaction).
    Expressions such as please, it will be appreciated if ..., kindly, etc. all function to soften the directness of the imperative.  For more, see the guide to suasion and hortation.
  3. These forms are addressed to someone (unless you are trying to encourage yourself) so are extrinsic in nature.
You are advised to take great care.
Visitors are not allowed beyond this point.
eye open
  1. You are advised to take great care.
    Visitors are not allowed beyond this point.
  2. The use of the passive voice is a common way to soften extrinsic obligation statements.
    In many cultures, it is virtually the only way in which adult-to-adult obligation is expressed at all.  It functions as a way of disguising the fact that what is really meant is something like
    I / we are telling you ...
  3. The use of passives restricts this use to extrinsic obligation.
The house needs painting.
That wants fixing.
eye open
  1. The house needs painting.
    That wants fixing.
  2. The use of the passive verbs like these in finite clauses is another is a common way to soften extrinsic obligation statements.
  3. These verbs can express intrinsic obligation if it is the speaker's duty to do the task and extrinsic obligation if used as a kind of imperative to someone else.
I must write to my mother.
I have to get my hair cut.
You ought to be more careful.
You shouldn't come without an invitation.
eye open
  1. I must write to my mother.
    I have to get my hair cut.
    You ought to be more careful.
    You shouldn't come without an invitation.
  2. Modal verbs are used frequently to express various levels of obligation.
  3. Both intrinsic and extrinsic obligation are expressed with all these examples.
This is necessarily the last word.
I was unavoidably delayed.
It's inescapably connected to politics.
It's somewhat important that ...
eye open
  1. This is necessarily the last word.
    I was unavoidably delayed.
    It's inescapably connected to politics.
    It's somewhat important that ...
  2. These are modal adverbs (acting as adjuncts) and there are plenty of them in English which imply various levels of obligation and duty.
  3. Mostly such expressions imply an extrinsic obligation but intrinsic obligation can be expressed by, e.g.
    I am somewhat obliged to help.
I think that's obviously what you do.
I feel this is probably the best way forward.
I imagine that's perhaps the best thing for me to do.
eye open
  1. I think that's obviously what you do.
    I feel this is probably the best way forward.
    I imagine that's perhaps the best thing for me to do.
  2. Here two things are happening:
    1. The speaker is using a projecting mental process verb to tone down the obligation.
      There are lots of these including believe, feel, guess, consider etc.
    2. The speaker is making the obligation less or more imperative by the use of adverbs.  Other examples include clearly, possibly, undoubtedly, patently, perhaps, maybe etc.
  3. Both extrinsic and intrinsic obligation can be expressed like this.
It is a vital task to get finished
That's an unnecessary addition.
That's a preferred option.
eye open
  1. It is a vital task to get finished
    That's an unnecessary addition.
    That's a preferred option.
  2. Modal adjectives like these are used in a similar way to modal adverbs.  They can express strong obligation (imperative, critical, essential etc.), a lack of obligation (needless, superfluous, avoidable etc.) and a prohibition (pointless, stupid, excessive etc.).
  3. This kind of structure is mostly confined to extrinsic obligation.
There's a great need for some hard work here.
The first prerequisite is ...
The No 1 necessity is for ...
It's your clear duty to write.
eye open
  1. There's a great need for some hard work here.
    The first prerequisite is ...
    The No 1 necessity is for ...
    It's your clear duty to write.
  2. Modal nouns like these are usually qualified in some way with an adjective which either makes them more or less urgent or obligatory.  Collocation is an issue because one can have a great / urgent / slight / imperative need but a big need or a high need are not possible.
  3. This kind of structure is mostly confined to extrinsic obligation, although the noun duty can work for both.
This is a bit urgent.
It's a tad important to ...
It's slightly important that I get there soon.
eye open
  1. This is a bit urgent.
    It's a tad important to ...
    It's slightly important that I get there soon.
  2. These are vague quantifiers or downtoners and used to affect the degree of obligation which is implied.  They almost always lessen it to the point where almost no obligation remains.
    Note, however, that the use of deliberate understatement can actually increase the level of obligation which is put upon the hearer.
  3. Both types of obligation are expressed this way.

More detail and exemplification follows.



Expressing obligation is frequently done via the use of pure and semi-modal verbs.  This is so obvious that some teachers confine their teaching of the function to the use of modal verbs alone.  That's a mistake.

The distinction between extrinsic and intrinsic obligation comes into play here, too.


pure and semi-modal verbs

We will consider these together but this is not a definitive list.  For more, see the other guides on this site to the various modal auxiliary verbs.

  Declarative Interrogative
Expressing obligation You must get this finished today Must we buy a ticket?
You should do it before Thursday Should I get some more help?
They ought to get more paint Ought we to try another way?
We have to stay late again this evening Do I have to do it now?
This needs to be done now Does this need to be sent?
Expressing prohibition You mustn't spend more than an hour on this Mustn't we sit over there?
You shouldn't work so late Shouldn't I get this done first?
They oughtn't to speak to her like that Oughtn't I to be a bit earlier that that?
You can't go in Can / can't we go in?
Don't you dare do that! No form.
Expressing lack of obligation They needn't do it urgently Do we need to do it today?
We don't have to finish tonight Does she have to be so demanding?
We haven't got to do it today Have we got to do it today?


  • ought to is often considered a semi-modal verb but, as can be seen from the examples, it functions in a very similar way, excluding the use of the to-infinitive, to pure modal auxiliary verbs.  Some consider the question forms with ought to be clumsy and Did we ought to ... is increasingly heard.
  • can / can't: The modal verb can is only used, in the negative only, to express prohibition.  It cannot be used to express an obligation to do something.  The positive and interrogative forms express permission (the other side of obligation's coin, of course).
  • dare in this sense is quite rare and there is no interrogative form for this function.
  • there is a small distinction between have to and have got to which may be worth mentioning at higher levels.  The insertion of got, which is mostly confined to BrE, can make the obligation sound stronger when the word is stressed.
  • It is often suggested that have to and ought to express extrinsic obligation but that must and should express intrinsic obligation.  There is little evidence for this and native speakers use the forms in free variation in most circumstances.  Evidence exists that the use of have to is increasing at the expense of must, at least in spoken BrE.  If this is true, the extrinsic-intrinsic distinction between the forms cannot be sustained.
    It is also the case that the extrinsic-intrinsic distinction is hard to sustain in many cases.  For example:
        I must / have to see the dentist about this tooth
        You must / have to learn the language if I want to live here
        They should / ought to avoid being late
        We shouldn't / oughtn't to spend so much on shoes
  • A more important and sustainable distinction between modal verb uses applies to repeated rather than one-off obligations.  For example:
        I have to get up early every day to catch my train to work
    implies that this is a repeated obligation, whereas
        I must get up early to catch the train tomorrow
    implies a one-off event.
    Equally, in the negative, lack of obligation can be signalled by:
        I don't have to get up early to catch a train to work
    which implies a continuous lack of obligation, whereas
        I needn't get up early tomorrow
    implies a one-off lack of obligation.
    Even here, however, native speakers will often use the forms in free variation unless they wish to mark the meaning in some way.
  • The semi-modal need often refers to epistemic modality but appears in the list above as a way of expressing deontic modality because it makes the obligation less personal and, therefore, more polite and distanced in many cases.

two marginal modal verbs

Two marginal modal verbs can express some sense of deontic modality: be supposed to and had better

be supposed to
can only be used to express obligation or prohibition.  It cannot express a lack of obligation.
  • You are supposed to be here at 9.
  • They are not supposed to use this in the evenings.
  • Aren't you supposed to be at work?
  • Are you supposed to use this program?
had better
can only be used to express obligation.  It is not used to express prohibition or lack of obligation.
  • You'd better get this done before you go home.
  • Hadn't you better ask before doing that?

modal adverbs, adjectives and nouns

modal adverbs
There were examples of these above using necessarily, unavoidably, inescapably, somewhat.
Other examples which heighten or diminish the sense of obligation are:
to some extent
to a certain degree
to some degree
As in, e.g., obviously important / patently unnecessary / manifestly urgent / somewhat useful etc.
modal adjectives
There were examples above (vital, unnecessary, preferred) to which we can add
These adjectives modify modal and other nouns and many of the derivable adverbs can be added to the list above.
As in, e.g.
a fundamental need / a crucial necessity / a pointless requirement / a critical prerequisite etc.
modal nouns
There were examples above using need, prerequisite, and necessity to which we can add must, essential, (pre-)condition, requirement and obligation but few others.  As was noted, these are almost always (but not always) modified in some way as in e.g.
a fundamental must / an imperative pre-condition / a desirable requirement etc.



It is noted above that the function of asking for and giving / withholding permission is the other side of obligation's coin.  A consideration of how it is done is appropriate here.

The line between epistemic modality and deontic modality can become slightly blurred here.  For example, look at the following expressions and try to decide whether they refer to obligation (deontic modality) or possibility (epistemic modality) and then click on the eye open to reveal some comment.

May I go now?
You may not go till it's all finished.
You may go when you like.
eye open
This is a clear case of deontic modality because the modal verb may refers to the lifting of an obligation to stay, the imposition of an obligation to stay or to a lack of obligation to stay.
The modal verb might is frequently used interrogatively only in the same way ask about obligation but it is unusual and formal
Might we go now?
Could I just say something?
Can I see you for a minute?
Do you have a moment?
eye open
These are probably cases of epistemic modality, referring to the possibility of something happening or the likelihood of a state existing.
However, they have a shade of deontic modality insofar as they can refer to whether there remains an obligation to stay silent or one not to interrupt somebody's day.
The modal verb could / can is often used in this way
Is there a chance of asking a question?
Do you have permission to be here?
eye open
These are something of a mixture of modality types:
Is there a chance of asking a question?
Is epistemic in the sense that it refers to possibility but may be deontic in the sense that it is asking whether there is an obligation not to ask a question.
Do you have permission to be here?
Is epistemic in the sense that it refers to the possibility of permission existing but deontic in the sense that it (probably) refers to an obligation not to be here.



The function of expressing obligation needs to be handled with great care if you want to avoid your learners sounding rude, intrusive and superior.

In most cultures, including English-speaking ones, it is simply inappropriate in most adult-to-adult interaction to use bare obligation forms such as

  • You must do this
  • Do it now!
  • You ought to go
  • It is necessary that this is done now

This is especially true between (comparative) strangers and in professional settings.  Even the most demanding boss is unlikely to use expressions of obligation without some form of softening and between other adults, unless they know each other very well indeed, the same applies
To teach exponents of obligation without simultaneously teaching ways to soften their effect is foolhardy and error inducing.

Here are some ways English has of softening obligation.

Tactic This ... ... is often softened to ...
Blame someone else You must get this finished today The bank needs these figures today
Do it before noon We'll need it before noon
Delete the subject, make it impersonal or use a passive form You mustn't spend more than an hour on this This shouldn't take more than an hour
Do this soon This has to be done soon
You can't leave yet Nobody can leave yet
You must work late tonight It's necessary for you to work late tonight
Insert politeness routines Take this to the post office Please take this to the post office
Can / Could you take this to the post office, please?
I wonder if you can take this to the post office
Use co-hortation instead of exhortation I require this done now Can we get it done now?
You must do this next week Can we agree to do this next week?
Use downtoners This must be done urgently This is a bit urgent, in fact
Please do this immediately Please do this as soon as possible

Tactics can be combined to get, e.g.:
I'm afraid this has to be done very soon
I'm sorry but this is extremely urgent

(If the terms co-hortation and exhortation are obscure to you, there's an explanation in the guide to suasion that may be of interest.)


Teaching this area

This is an area at which learners of the language tend to fall into two camps: those who avoid any kind of obligation statement for fear of causing offence and those who cause offence by overusing direct forms.

As we saw above, the area is complex and there is a range of ways to express obligation, its lack and prohibition.  We can, if we are not careful, overwhelm our learners so the area needs to be approached piecemeal, one or two structures at a time.


other languages

As we have seen, English deploys some eight modal and semi-modal verbs as well as a range of less direct modal expressions and the imperative mood.
Other languages, as you may imagine, do things differently.

  • Some languages rely on a very limited range of modal verbs and, therefore, use many more adjectival, adverbial and verbal constructions.  This can make them sound overly formal in English, for example:
        It is necessary that I go now (instead of I really ought to go)
        Am I obliged to stay? (instead of Do I have to stay?)
        Is it compulsory to be here? (instead of Must we be here?)
  • Some languages rely on a complex range of tense forms, avoiding any directness at all so all obligations are couched in non-personal or passive ways.  Speakers of these languages find it difficult to identify comparable constructions in English and produce odd-sounding language such as:
        Someone says this is to be done (instead of We need to do this)
        These letters are to be posted by someone (instead of Please post these letters)
  • Some languages allow a great deal more directness, especially with the equivalent of must,  than English does and speakers of these can sound almost abusive, certainly quite direct or rude.  For example:
        You must come to my house at six
        You must buy a new car
        You hair needs cutting


A little comparative language work in the classroom can expose these differences, is quite interesting and can positively contribute to learners' ability to select the correct tone in what they say.


power relationships

Above, when discussing the relationship between obligation and advice, it was noted that the same expression of deontic modality can imply anything from mild advice to strict obligation depending on who is talking to whom.  So, for example,
    You should not park here
is a statement of prohibition you would foolish to ignore from a police officer but merely advice it is safe to disregard if it comes from a friend or a child.
    You must look at this
can, from a friend, simply mean
    This is interesting (so my advice is to look at it)
but from a teacher to a pupil may mean
    Look at this! (or there will be unpleasant consequences)
Making role relationships clear when introducing the area or practising the exponents is, therefore, vital.
Pictures of settings and participants often help:

navy advice advice couple chatting

raising awareness

A simple approach is to start with recognition of an appropriate expression of obligation.  Like this:

Discuss with a partner and put a tick in the right box.
Situation Statement Too direct Too indirect About right
Customer to waiter You must bring me a clean knife.      
Bring me the menu.      
You should leave the bottle here.      
Please bring me a clean knife      
Can you leave the bottle here, please?      
Boss to employee You have to work late today      
We all have to work late today, I'm afraid
We must get this job done even if it means working late      
These reports need copying      
Copy these reports      
Get these reports copied      
Friend to friend See a doctor      
You should see a doctor      
You must see a doctor      
I would suggest seeing a doctor if you have a little time      

The same kind of approach can, clearly, be taken for the other strategies in the table above.

focusing on form and strength of obligation

Statement Strong obligation Weak obligation Strong prohibition Weak prohibition No obligation at all
Do this before lunch          
Bring me the menu.          
Please get these copied before the meeting          
I may be important to do this soon          
It is critical that this is corrected          
Please don't feel obliged to do this if you don't have time today          
These tables ought to be cleaned
You don't have to work late but it would be nice          
We should get on with the meeting          
You should stop now.  We are running out of time.          

public notices

At lower levels especially, all sorts of notices are useful for identifying the strength of obligation / prohibition / lack of obligation they imply.  Be aware, however, that beyond the basics of must, have to, don't have to, should and shouldn't their usefulness ends.  Using them requires some intensive concept questioning along the lines of
    What must you do?
    What do you have to do here?
    What mustn't you do?
    What shouldn't you do?

For example:

sign sign sign sign
sign sign sign sign


Above this level, it is necessary to be a bit more imaginative and create and discuss scenarios in which the expression of obligation is required and some subtlety needed in its use to ensure it's appropriate.  Some ideas for settings in which obligation can be considered are:

  • the workplace
    E.g.: How are different roles subject to different obligations.  Does the boss have to be at work at 9?  Who has to work late most often?  Who can eat where? etc.
  • schools and colleges
    E.g.: What rule are relaxed as children get older?  How are obligations different between school and university? etc.
  • hotels and guest houses
    E.g.: What rules differ depending where you stay?  What obligations are imposed on staff and guests? etc.
  • staying with a host
    E.g.: What home rules would you impose?  What duties do guests have?  What kind of behaviour is permitted? etc.
  • doing dangerous sports
    E.g.: What must one do?  What should one do?  What is it advisable to do? etc.
  • visiting a hospital
    E.g.: What should one do?  Where is one allowed to go?  When are you permitted to visit? etc.
  • using a computer safely
    E.g.: What should you avoid?  What must you never do?  What advice should you take? etc.

All of the above allow for a good deal of speculation concerning what is required, what is recommended, what prohibited and what allowable with various gradations of strength.
Obviously, your learners can't approach the scenarios until they have understood at least something of the possibilities in English.  That, we have to teach.

Related guides
non-modal verb modality for a guide to modal adverbs, adjectives and nouns
expressing (un)certainty for more on epistemic modality
suasion and hortation for more on the imperative and other ways of affecting the behaviour of others
causatives for a guide to a related area not considered at all in this guide
the modality index for guides to the expression of various forms of modality in English