Modal auxiliaries and related verbs
General features of modal /GB 'məʊdl US 'moʊdl/ auxiliaries
1.1. General functions
1.1.1. To express permission, advice, command etc
1.1.2. To express different levels of politeness
1.2. Grammatical characteristics
1.2.1. Full modals: can, could, may, might, will, would, shall, should, must, ought to
1.2.2. With only some features of the above: need, dare, used to
1.2.3. Words that can function as modals and as full verbs: need to, dare to
1.2.4. Full verbs similar to modals: be, have, do
1.3. Differences between modals and full verbs
1.3.1. Modals cannot be used as infinitives (e.g. to be vs *to can vs to be able to)
1.3.2. Modals are followed by bare infinitive not to-infinitive (e.g. be to vs *can to, exception: ought to)
1.3.3. Modals have not -ing
1.3.4. Modals have no –(e)s in 3rd pers sg
1.3.5. Tense labels (present, progressive, past, perfective) often cannot be applied to modals as they are applied
to full verbs:
 I can/may do it refers to present or (immediate) future
 She may be phoning him has progressive of phone not may
 Perfect and past: MODAL + HAVE + PAST PARTICIPLE needs not imply present perfect meaning as we know it
from full verbs
 Real past forms of modals
 Can/will/may/must appear in only reported speech: He says you can...  He said you
could..., He tells me I must wait...  He told me I must (had to) wait...
 Might for historical narrative: In the 14th c. a peasant might have the right to.... Otherwise it
expresses uncertainty.
 Could to express ability in the past: He could (was able to) swim when he was a boy.
Otherwise it’s a polite alternative to can.
 Would may be used for past reference: When we were young we would spend our holidays
there. Otherwise to express refusal in present or past He wouldn’t listen. or sth less likely It
would seem as if...
1.4. Differences between modals and be/have/do
1.4.1. Modals as auxiliaries have a basic meaning of its own, be/do/have as auxiliaries have only a grammatical
function
1.4.2. Most modals (and do) don’t have contracted forms in the affirmative Be/have (exceptions: will  ’l and
would  ’d)
1.4.3. We can have only one modal per verb phrase, be/do/have can in some contexts be used together, e.g.
have been, do have to vs *We may must call a doctor.
1.5. Similarities between modals and be/have/do
1.5.1. The negative: not is added after modals just as after be/have/do (is not vs cannot)
1.5.2. Questions
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yes/no question by inversion;
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wh-questions modals and be/have/do preceded by Wh-word;
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tag questions the same: don’t you vs can’t you;
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negative questions with not after subject: Can you not help me? Can’t you help me? vs Do you not
like him? Don’t you like him?
2. Functions
2.1. Primary: can/could for ability, may/might for permission, will/would for prediction, should/ought to escapable
obligation, must inescapable obligation, needn’t absence of obligation
2.2. Secondary: to express degree of certainty:  UNCERTAIN – might – may – could – can hardly etc – should –
ought to – would – will – must – CERTAIN  . No shall here.
3. Ability
3.1. Modal: can/could Full: be (un)able to, be (in)capable of, manage to, succeed in
1.
3.2. Can and is able to are interchangeable for present reference unless we are commenting on sth that’s happening
right now: Look, I can stand on my hands!
3.3. Can have for possibility not ability He can’t have told you anything I don’t already know.
3.4. Could for ability in the past unless related to a specific event, see question Error! Bookmark
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not defined.
above and then answer below ;-)
3.5. Could have = would have been able for ability in the past in conditional sentences if independent circumstances
are involved: If it hadn’t been for the wind the rescuers could have reached them.
3.6. Can/be able to with verbs of senses at the moment of speaking I can’t see anyone. and in the past I could
understand it easily.
3.7. Could = would be able to for ‘unreal past’ sometimes with if-clause implied: You could get into university (if you
applied).
3.8. Could to express surprise anger etc at present: I could slap your face.
Can/could be for possibility at present or past: It can be cold at high altitudes. or even future: It can be cold
when you get there.
Permission/prohibition
4.1. Modal: can/could/may/might; Full verbs: be allowed/permitted/forbidden to, be prohibited, be not to You’re
not to smoke, negative imperative Don’t smoke!
4.2. Hesitancy scale:  NEUTRAL/INFORMAL – can – could – may – might – HESITANT/POLITE  Can I borrow it? is
commonest and most informal. Modifications with possibly, be allowed etc possible.
4.3. Pressing for affirmative answer Can’t/Couldn’t I stay till midnight (please)?
4.4. Could can express permission in general As children we could (were allowed to) watch Baywatch.
Certainty and possibility
5.1. Modal: may/might/could/must/should/ought to; Full verbs: is etc. E.g. certainty: She must be/is/works at home.
5.2. Questions about possibility: Might/Could/Can this be true? Couldn’t/Mightn’t he be at home now?
5.3. Negative possibility: He may not be (have been) here.
5.4. Scale of certainty:
5.4.1. positive  FACT – is – could be – should be – ought be – may be – might be – UNCERTAINTY  e.g. He could
be at home.
5.4.2. negative  FACT – isn’t – can’t be – couldn’t be – may not be – mightn’t be – UNCERTAINTY  e.g. He
mightn’t be at home.
Deduction
6.1. Modal: must/can’t/may/might/could/should/ought to/will/won’t; present: He must be here. She can’t be
leaving. past or perfect: He must/can/can’t/couldn’t have been (working) here.
6.2. Can’t be (not *mustn’t be) is the negative of must be
6.3. Can’t have been is the negative of must have been
6.4. In AmE have (got) to be also possible
6.5. Will/won’t That will be him.
Offers, request, suggestions
7.1. Modal: can/could/will/won’t/would/wouldn’t/may/might e.g. Won’t you have some coffee? What will you
have? Might I have a sandwich?
7.2. Typical responses e.g. Shall we go for a swim? – Yes, let’s, (shall we?) – Yes, I’d love to. – No, I’d rather we didn’t.
– No, I’d rather not.
Wishes
8.1. Modal: want; Full verbs and phrases: wish, if only, it’s (high/about) time
8.2. After these we use
8.2.1. The past tense to refer to present time: I wish/If only she was here now. Or with subjunctive: I wish/If
only she were here now. I wish/If only she knew the answer.
8.2.2. The past perfect tense to refer to past time: I wish/If only she I had been here yesterday. If only implies
regret, I wish not necessarily
8.2.3. I wish/(if only) you etc would/could to refer to the future and to make general wishes: I wish you would
be quiet. I wish I could have been with you. Would implies willingness, could ability.
8.2.4. Phrases or obsolete expressions: Would that it were true! Would to God I knew! Would to God I had
known!
8.2.5. If can be separate from only: If he was/were only here. If I had only known!
8.2.6. It’s (high/about) time: with past tense or subjunctive to refer to present or future: It’s (high/about) time
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he was/were taught a lesson. Isn’t it about time our baby could (*would) walk?
Preferences with would rather/sooner
9.1. Would + rather/sooner + bare infinitive – expresses personal or sb else’s preference:
9.1.1. Present I’d rather/sooner be a miner than a clerk.
9.1.2. Past If I’d lived in 1400 I’d rather have been a knight.
9.1.3. Modifications possible: I’d (far/much) rather/sooner be young than old.
9.1.4. Would rather/sooner + clause in past tense: I’d rather/sooner he left on an earlier train.
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The past with present or future reference: I’d rather you were happy.
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The past perfect with past reference: I’d rather he hadn’t told me about it.
Advisability
10.1. Modals: should/ought to/had better
10.2. Scale of choice  ADVISABILITY – should – ought to – had better – is to – need to – have got to – must – NECESSITY
 e.g. I have (got) to check the oil level.
10.3. Must in public notices: Cyclists must dismount.
10.4. Questions: Must you always interrupt?
10.5. Need as a modal: Need you (always etc) leave so soon? – Yes, I have to. – No, I needn’t have.
10.6. Present or future: should/ought/had better to etc: I had better leave (before 9 tomorrow).
10.7. Future: I’ll need/have to be leaving before 9 tomorrow.
10.8. Perfect/past: I should/ought to have been at the office earlier.
Lack of necessity, inadvisability, prohibition
11.1. Needn’t = don’t have to = haven’t got to
11.2. Present: You needn’t go there. You shouldn’t start smoking. You can’t park here. Past: You needn’t have gone
there. You shouldn’t have started smoking. You shouldn’t have parked here/You ought not to have parked
here.
11.3. Scale of choice  INADVISABILITY – shouldn’t – oughtn’t to – had better not – is not to – can’t – mustn’t –
PROHIBITION  e.g. You’d better not overtake here.
Habit: used to/will/would
Dare as modal and full verb, daresay
Other uses: may/might/shall/should