Central modal auxiliary verbs
There is a general and simpler guide to modality and modal auxiliary verbs which you could follow before you access this area if it is new to you (new tab if you go there).
This guide
focuses only on true, central or pure modal auxiliary verbs. All
three terms are used in the literature but we are sticking with
central to distinguish these verbs from those that are modal
auxiliary verbs but are more peripherally so because they do not conform
to the tests we shall apply.
There is another
guide to
semi-modal auxiliary verbs, linked in the list of related guides at the
end, which covers dare, let, need and used to
and marginal modal auxiliary verbs such as seem to, tend to, be about to etc.
We are also sticking with the rather clumsy expression modal
auxiliary verb because it is necessary to bear in mind that
there are other modal verbs which are not auxiliaries such as guess,
imagine, oblige, suggest, force, intend and so on which carry modal
meanings of some kind as, indeed, do a range of modal adjectives,
adverbs and nouns.
Often, these verbs are simply called modals or modal verbs but that's
shorthand and we'll avoid it here.
An alternative view is presented in
the guide to
types of modality also linked at the end.
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In what follows ... |
What follows is a guide to the main central modal auxiliary verbs in English, taken one
by one. We will look at the possible
functions of each verb and
how it is used.
In the notes
following each table, areas which cause specific and predictable
problems for learners are often indicated. It is these in particular that you must be
able to analyse and explain in the classroom.
Tests in sections of this page only exist for the more complex verbs but
there's a link to a test on all of them at the end.
The identification of central or pure modal auxiliary verbs is often limited
to 10 verbs:
can | could | may | might
| must | shall | should | will | would | ought
In this analysis, however, the verb had
better
is included because it shares some structural characteristics
with the central ten.
Elsewhere, you will find verbs included in or excluded from this
list. In particular, the verb ought is often excluded
because it is usually followed by the to-infinitive. That
is not universally the case, however, and in AmE particularly uses
like:
You oughtn't come if you are tired
or
Ought I go?
are frequent and they may be encountered in the production of BrE
speakers.
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Ten tests for central modal auxiliary verbs |
If you have followed the essential guide to this area you
may recall some of the following section. Here, we have extended
it a little to include some less commonly noted characteristics of
central modal auxiliary verbs. There are 10 in all.
Traditionally, in order to be included as a pure or central modal
auxiliary verb, the verb needs to conform to all these tests:
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Central modal auxiliary verbs cannot co-occur |
So, for example:
*I must can do it
*I will must do it
are impossible because must, will and can are pure
or central modal auxiliary verbs. However
I may be able to do it
I will have to see him
are possible so
be able to and have to are not, by
this test, central modal auxiliary verbs. The former, in fact,
is simply a modal adjective used with the copula.
Lexical or main verbs, on the other hand,
can occur together and often catenate as in, e.g.:
She wants to help to do the work
They enjoy sitting by the fire on a winter's evening
etc.
Semi-modal auxiliary verbs may also co-occur so we may encounter,
for example:
I didn't dare let the dog go
I used to need to get up very early
etc.
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Central modal auxiliary verbs do not inflect for person |
Central modal auxiliary verbs carry no inflexions. So in, for example:
She wants a cup of tea but I had one earlier
the lexical or main verb
want changes to wants with an added -s
to show who we are talking about.
Central modal auxiliary verbs remain unchanged for person so, for
example:
*She musts come
*It wills rain
are disallowed.
Semi-modal auxiliary verbs do sometimes inflect so we may find:
She needs to leave
He dares to ask
Again, the verb used as a semi-modal auxiliary verb is
exceptional because it never inflects for person. The
past-tense inflexion (d) is optional in some circumstances
with that verb.
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Central modal auxiliary verbs have abnormal time references |
- Lexical or main verbs may or may not inflect regularly to
form a past tense but the relationship to time remains clear so,
for example:
He hopes to come
She does the work
and
He hoped to come
She did the work
are distinguished by the tense ending inflexion or by an internal change to the verb.
(Fewer than 20 verbs in English do not inflect at all for tense but the zero inflexion in these cases is still applicable to tense so, for example:
She quit her job
and
I cut my finger
are still or may be past forms.)
Some modal auxiliary verbs have past forms so:
He can come
can be expressed in the past as
He could come
He will do
can be expressed in the past as
He would do it
I shall be there
is sometimes expressible in the past as
I should be there
and
She may go
has a past form in
She might go - Except for the unusual verb used,
semi-modal auxiliary
verbs do inflect for tense and do so with the same significance
as lexical or main verbs imply so we can encounter:
She needed to get here early
I hadn't dared to ask her
etc. - Where they exist, past forms of central modal auxiliary verbs
may be used to refer to present and future time (often
with a more tentative sense) so we get, e.g.:
She could come tomorrow
She might be angry
I would love to come
Past forms of lexical or main verbs cannot perform this present-time function. - The central modal auxiliary verbs must and ought (to) have no tense forms at all and could as the past of can or might as the past of may are restricted to certain meanings (see below).
- Some central modal auxiliary verbs have alternative verb forms to express other tenses which are in themselves not central so have to is often used to form the past and future of must and be able to has the same function for can and could. Some of these alternatives are discussed in this guide.
- When a central modal auxiliary verb is used in a past form
such as in:
She should have come
They ought to have been there
It must have snowed last night
etc.
the sense of the present perfect which would be implied with a lexical or main verb of embedding a past in the present is not apparent. So, for example:
I have finished
refers to the present state with the past embedded within it (it's a present perfect form) but
I should have been kinder
does not necessarily carry the sense of present relevance and may just be reference to a finished event which has no present relevance. However, because modal auxiliary verbs express the speaker / writer's current view of an event or state, some sense of present relevance is often maintained.
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Negatives of central modal auxiliary verbs are formed by the inclusion of the negator not after them |
Most
of these verbs allow the negator to be contracted to n't which is
added to the verb so, for example:
I will not do it
Mustn't she come?
I can't go
You shouldn't really
are all possible,
but
*I didn't the work
*I talked not to John
*They don't should be here
*I don't must come
etc. are not possible because lexical or main verbs are negated with the
do operator in the simple present and past tenses and must and should are central
modal auxiliary verbs.
The verb will whether it is functioning as a central modal
auxiliary verb or as a primary auxiliary verb referring to the
future is unusual in that the vowel mutates from 'i' to 'o'
and loses the ending when the negator is appended. Thus we
have won't not *willn't.
The verbs may and shall are infrequently negated with a contracted
form of not so:
She mayn't be there
I shan't arrive late
are quite rare even in BrE and almost impossible in other varieties.
Semi-modal auxiliary verbs sometimes form their negatives with the
simple addition of n't / not but are also able to form the negatives
with the do / does / did operator as in:
He usedn't to be so grumpy
He didn't use(d) to be so grumpy
She daren't go
She doesn't dare go
etc.
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Interrogatives are formed by simple inversion of the verb and its subject |
As in:
They must do it → Must they do it?
He can see it → Can he see it?
She will be early → Will she be early?
and negative questions are formed in the same way:
Mustn't we do it?
Won't we be late?
Can't we go now?
etc.
Lexical or main verb questions cannot be formed this way because they
require the do operator so:
Did you the work?
Talked not you to John?
are not encountered in Modern English.
Semi-modal auxiliary verbs can also form questions by simple
inversion (although this is becoming rare) or by using the forms of
lexical or main verbs so we get, e.g.:
Did he use(d) to work here?
Used she to be a teacher?
Did she need to pay?
Need she have asked?
Did she need to ask?
Dared she complain?
Did she dare complain?
etc.
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Central modal auxiliary verbs cannot be non-finite |
So while, for
example:
Opening the parcel, he was delighted to find the new lens
She wants
to go home
are possible non-finite forms of lexical or main verbs,
but no such form exists
for central modal auxiliary verbs and:
*Musting go early, he ran off
*To can do it is a useful skill
are not permitted.
Semi-modal auxiliary verbs are also possible in non-finite forms so
we see:
Daring his displeasure, she put up her hand
Needing to leave urgently, they called a cab
etc.
The semi-auxiliary verb used is an exception and is not
seen in the non-finite form so there are no forms *to used
or *useding.
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Quantifiers which modify the subject of the clause may occur after a central modal auxiliary verbs |
So we allow, for example:
They can all be here
The sisters must both pay for a ticket
etc.
This cannot occur with lexical or main verbs so:
*They hope all to come
*They do both the work
are disallowed because the determiner must precede a lexical
verb as in:
They all hope to come
They both do the work.
Semi-modal auxiliary verbs occupy an uneasy middle ground. We
may encounter:
They all dared to swim
but not
*They dared all to swim
and
They used all to work well together
as well as
They all used to work well together.
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Reduced clauses with ellipted complements can be used with central modal auxiliary verbs |
So we allow, for example, we see:
She can be there if you can
They said they could come to the party but couldn't in the
end
where the main verbs, respectively be and
come, are ellipted.
Lexical or main verbs are not used in this way so:
*I hope to be there if you hope
*She spoke about the problems as you spoke
are not permitted because, again, the
do operator it
required as a substitute for the verb.
Semi-modal auxiliary verbs share this characteristic to some extent
but can also occur with the do pro-form so we see:
She used to be as happy as he did
They dared ask one question but didn't dare two
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Central modal auxiliary verbs cannot be emphasised with the do operator |
Emphasis in denying a negative assumption or placing stress on
the verb is achieved with lexical or main verbs by the use of the do
operator as in:
We do hope to be there
No, you're right, I do smoke too much
I did like the music
but this cannot be achieved with central modal auxiliary verbs so:
*I do can be there
*She does must have more time
*I do should go now
are not allowed and adverbials such as
definitely, in fact and really are used instead.
Semi-modal auxiliary verbs may be emphasised with the do
operator as in:
They did dare to swim
She does need to go
He did used to drive too quickly
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Time adverbs of indefinite frequency may (not must) follow central modal auxiliary verbs |
So we allow, e.g.:
I should usually
be there
I can often meet him
but
*I smoke often too much
?*She arrived frequently late
are rarer when they are allowed at all.
Semi-modal auxiliary verbs can operate in both ways so we allow:
She used frequently to start early
She dared often to stay out late
She needed occasionally to ask for help
and
She frequently used to start early
She often dared to stay out late
She occasionally needed to ask for help
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One by one |
You can use this menu to go to the verb which interests you or
work through the page, taking the tests as you go along.
The comments here cover the main uses of each verb and are not entirely
exhaustive.
could might should would must can may will shall ought to had better
Clicking on -index- at any time will return you to this menu.
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could / was able to |
| That could be the postman |
Essentially, could performs the following functions in English but the expression was able to is more restricted because it usually only refers to a specific instance of an ability and is always a past time marker. The word able in this setting is purely adjectival.
| Function | Example | Restrictions with was able to |
| present possibility | That could be the postman now. | was able to is not possible: *That was able to be the postman |
| future possibility | It could rain tomorrow. | was able to is not possible |
| past possibility | He could have seen her. I'm not sure. | was able to is not possible |
| present ability | I could do that. | It is possible to replace this with the
present tense but not with the past form in this meaning: I am able to do that |
| present offer | I could help with that, if you like. | It is possible to replace this with the
present tense: I am able to help with that but this refers to ability not to an offer. (See under can below.) |
| future ability | I could finish in an hour if I get some peace. | was able to is not possible |
| past ability | When I was only two, I could swim pretty well. | was able to is possible: I was able to swim pretty well |
| permission | Could I ask you a question? | was able to is not possible |
| complaint | You could have warned me! | was able to is not possible |
Notes:
- Present possibility and
future possibility are not always easy
to distinguish. For teaching purposes, it's rarely important
to do so because the forms and functions are the same. For
example:
A: Are you coming to the meeting?
B: I could do.
is an exchange which can apply to right now or the future because we do not know when the meeting will be. - Most uses of could refer to possibility or
ability.
She could have left her keys with John
can refer to both possibility and ability. It means either:
John offered to look after the keys so she was able to leave them with him
or
It is possible that she left her keys with John (and that's why she can't find them now)
Only the second use of could can be replaced with might (see below). - be able to is only an alternative if the sense
expresses ability.
General
ability in the past
can be expressed either with could or was able to:
I could speak French = I was able to speak French.
However, if we refer to a specific instance of success, only was able to is possible:
I was able to remember the word in French
not
*I could remember the word in French.
This restriction does not apply to negative or interrogative clauses so:
I wasn't able to remember the word in French
I couldn't remember the word in French
Were you able to remember the word in French?
Could you remember the word in French?
I wasn't able to swim when I was a child
I couldn't swim when I was a child
Were you able to swim as a child?
Could you swim as a child?
are all allowed. - When used for permission, could is generally confined to tentative, polite questions.
- For the negative deduction uses of could/couldn't have, see under must below.
- When used for complaints, the verb is usually interchangeable
with might and always in the past form. So:
You might have told me = You could have told me
with very little, if any, difference in meaning. - When used for future ability or possibility, the question forms
often imply a request rather than an enquiry about
ability or
possibility. For example:
Could you open the door?
is not about enquiring about future ability. It is usually a request.
However, it could be enquiring about past ability and mean:
Were you able to open the door?
or it is a request for some help and means:
Please open the door.
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might |
| There might be a snake in the hall |
Essentially, might performs the following functions in English:
| Function | Example |
| present possibility | Careful. There might be a snake in the hall. |
| future possibility | It might rain tomorrow. |
| past possibility | He might have telephoned while I was out. |
| suggestion | You might try taking an aspirin. |
| permission | Might I talk to you? |
| complaint | You might have warned me! |
Notes:
- Some of these are quite unusual and wouldn't be taught at lower levels. E.g., might for permission and suggestions.
- might never refers to ability
so:
She might have left her keys with John
can only refer to possibility. it means:
It is possible that she left her keys with John (and that's why she can't find them now)
This use of might can also be replaced with could (see above). - The negative of the use for permission is usually expressed with
mustn't or can't:
We mustn't/can't go
not
We mightn't go
because that implies an unlikelihood. - The negative of the use for past possibility:
when the speaker is quite sure of something this is usually expressed using couldn't have / can't have:
He couldn't / can't have got out
when the speaker is unsure we use might:
He might not have tried to telephone me - might is often seen as adding 'distance' – making
possibilities less likely and requests or suggestions more polite.
Compare
It could rain
It might rain
Could I go now?
Might I go now?
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should |
| You should take an aspirin |
Essentially, should performs the following functions in English:
| Function | Example |
| advice | You should see a doctor. You should have called me. |
| obligation present, past and future |
You should not talk that way! You shouldn't have said that. |
| conditional uses | We should love to come (if we are
invited). (See note 2) Should you need any help, just ask. |
| logical deduction | Mary should be home soon. They should have arrived by now. |
Notes:
- The distinction between strong advice and obligation is often blurred – the roles of the speakers usually give the game away. If someone in authority such as a teacher or manager uses should it usually expresses obligation.
- The conditional use of should for 1st person forms
instead of would is often seen as formal and pretty much
confined to British English. This is also called the
contingent use.
In the past we prefer:
We would have loved to come but were away at the time
to
We should have loved to come but were away at the time
although both are possible. - should is occasionally used in rather odd, formal expressions
such as:
I regret that it should have happened.
This is the putative use of the verb.
Arguably, the contingent use of this verb is a tense form and, therefore the verb is acting as a primary auxiliary verb.
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would |
| He would often take his dog |
Essentially, would performs the following functions in English:
| Function | Example |
| request/volition | Would you leave me alone, please? |
| conditional uses | You would be in danger if you tried it without training. |
| habit | We would always have tea at 5. |
| characteristic | That's just the sort of thing he would say. |
Notes:
- Would is one of the most common words in English, ranking approximately in 60th place.
- The conditional uses are extremely common. This is also called the contingent use.
- When used to describe past habit, it
frequently follows an initial use of
used to and often expresses nostalgia. As in, e.g.:
We used to take our holidays in France where we would stay in a small guest house and would eat good, local food every evening. - When followed by rather, with or without ... than
..., the verb indicates preference:
I'd rather stay in and watch television (than ...). - There is a slightly unusual use of would to express an
uncertain deduction about a past event (see under will below). Compare,
e.g.,
That'll be Mr Brown you saw in the classroom
which implies the speaker is more confident than:
That would be Mr Brown you saw in the classroom.
Arguably, would also functions as a tense-forming primary auxiliary verbs to which there is a guide linked below.
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must / have to / needn't |
| That must be her sister |
Essentially, must performs the following functions in English:
| Function | Example | Restrictions with have to and needn't |
| obligation | Must I take the test? | None. Do I have to take the test? No, you needn't take the test No, you don't have to take the test |
| logical deduction | That must be his brother. Aren't they alike? | needn't is not possible in this meaning |
| advice | You really mustn't make such a fuss. | Neither needn't nor have to can be used in this sense because they imply a greater sense of negative obligation. |
Notes:
- The difference between strong advice and obligation is often very blurred (if it exists at all). Much depends on the authority with which the speaker is endowed.
- must can be replaced by have to in certain
circumstances only.
- External vs. internal obligation:
it is often asserted that have to implies an external
obligation but must refers to an internal one.
Compare
I must get this done
which can mean that this is a self-imposed obligation, with
I have to get this done
which can imply an external obligation.
Too much can be made of this dubious distinction and it's probably not worth teaching it because native speakers use the verbs in free variation in most cases.
It is also difficult at times to state categorically whether an obligation is internal or external especially if there is little context. - Tenses: must used for obligation has no future or past forms
(but it does in the sense of
deduction, see note 4.) so the use of have to is
obligatory in, e.g.:
I had to do it yesterday
We'll have to wait and see
etc. and:
*I must do it yesterday
is not allowed, although
We must wait and see
expresses current obligation with a prospective aspect.
- External vs. internal obligation:
it is often asserted that have to implies an external
obligation but must refers to an internal one.
Compare
- The negative of must for obligation
has two forms:
- No obligation: needn't / don't have to
You needn't / don't have to go)
Only didn't have to / didn't need to express a lack of obligation in the past. The expression needn't have suggests something was unnecessarily done. Compare:
He didn't need to do it (so didn't)
with
He needn't have done it (but did). - Negative obligation is expressed with must not
You mustn't go
- No obligation: needn't / don't have to
- The negative of the use for deduction in standard British English is formed with could
not or cannot:
He can't have done it by himself
It couldn't have been the same man
However, in some varieties must not is used for a negative logical deduction. - Interrogative clauses asking for speculation or deduction are
also formed with can and
could as in, e.g:
Can it have been forgotten?
or
Could that be her mother?
so:
Must it have been forgotten?
refers rather oddly to obligation and
*Must that be her mother?
is disallowed.
- The deductive sense of
the verb does have a past form:
He must have escaped
etc.
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The types of obligation signified by have to |
A certain mythology has grown up around the use of must vs. have to to express obligation which it may be as well not to allow to propagate too widely. In particular:
- We noted above (2a) that it is sometimes averred that have to applies to external
obligation placed on a person and must is used for internal
senses of obligation and duty. It follows that:
I have to write to my mother
is an obligation placed on me by another and
I must write to my mother
is a sense of duty I am imposing on myself to commit to an action.
This is a very doubtful assertion and the forms in the present tense are used in free variation by many speakers with those from the USA, in particular, often preferring have to to must in all senses.
Furthermore, it is not always clear whether an obligation is internal or external so, for example:
This tooth is getting worse and I must get to a dentist
is as likely as:
This tooth is getting worse and I have to get to a dentist
There are other problems with this assertion:- It cannot apply to past and future forms because must
is structurally unable to occur so:
I had to write to my mother
or
I will have to write to my mother
cannot be compared to some kind of internal obligation using must because no form with that verb is available. - have to (like must) can
signify other forms of modality so, for example:
He must be the bride's father
cannot be contrasted with
He has to be the bride's father
because neither sentence denotes any kind of obligation, internal or otherwise. The sense concerns the likelihood of a proposition being true and that is epistemic modality.
By the same token:
The answer must be between 0 and 1
cannot be contrasted with
The answer has to be between 0 and 1
because, again, neither sentence refers to obligation at all but to a necessary truth.
- It cannot apply to past and future forms because must
is structurally unable to occur so:
- It is also suggested that must refers to a specific obligation
and have to refers to more general obligations so, it is averred:
I must tell her the truth
is correct and so is:
We have to tell the truth at all times
but the alternative formulations:
I have to tell her the truth
and
We must tell the truth at all times
are somehow wrong.
That is nonsense, of course, and the same issues with other tenses intervene to show that. The only way to express the past or future obligation is:
I had to tell her the truth
I will have to tell her the truth
and
We had to tell the truth at all times
We will have to tell the truth at all times
so, whether the obligation is general or specific cannot be a consideration. The same applies to the insertion of progressive or perfect aspects. - Finally, it is also often suggested that we use must to
refer to duties we impose on others and we reserve have to
to imply that the obligation comes from elsewhere (a similar but
slightly subtler idea than the external-internal distinction).
So, it would follow that we should prefer:
You must be careful (because I require it)
to
You have to be careful (because other authorities require it).
There is slightly more substantiation for this distinction and little doubt that some English speakers will prefer have to to signify a rule and must to signify a personal admonition so making a difference between:
Must I wear a uniform?
to mean:
Do you insist that I wear a uniform
and
Do I have to wear a uniform
to mean
Is there a rule about uniform wearing?
However, whether this distinction exists is slightly doubtful and whether it is worth troubling most learners with it is even more doubtful. It is unlikely that most native speakers would wince if the modal auxiliary verbs were used in reverse.
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can / be able to |
| She can't get out |
Essentially, can performs the following functions in English but be able to is more restricted in use because it only refers to ability. It is, in fact simply a dynamic modal adjective phrase.
| Function | Example | Restrictions with be able to |
| ability | Can you do it before tomorrow? | Are you able to do it? |
| permission | You can go now. | be able to is not possible in this sense |
| possibility | The weather can be dreadful in March. | be able to is not possible in this sense |
| request / offer | Can you help me? Can I help? |
Are you able to help me? Am I able to help? are both possible but do not carry the sense of a request as they refer to ability only |
Notes:
- When the request form uses the 1st person, it functions as an
offer:
Can I help? - The negative of the permission function can be expressed using
can or must:
You can't leave yet
You mustn't leave yet - cannot have / can't have only occurs as negative past deduction (see under must). It is not used for permission or ability in the past.
- be able to is only an alternative if the sense
expresses ability:
I can speak French = I am able to speak French
However, able to is not possible in other senses: you can't give permission by saying:
*You are able to ask questions at the end
and there is a functional difference between:
Are you able to help me?
and
Can you help me?
The first enquires about ability and the second about willingness so it's a request.
Like must, can has no future form (although it does have a past in some senses of ability only, see under could, above). For this reason, future senses are expressed as follows:- Future ability:
She will be able to help tomorrow
She can help tomorrow
In the second of these examples, there is a possible ambiguity because it also has the meaning of
I will allow her to help tomorrow - Future permission:
They will be allowed to go later
They can go later - Future possibility:
The weather might be dreadful next March
but
*The weather can be dreadful next March
is not possible).
- Future ability:
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may |
| May I ask a question? |
Essentially, may performs the following functions in English:
| Function | Example |
| permission | May I sit here? |
| possibility/doubt | That may be his brother. |
Notes:
- The permission use is often seen as a more formal version of can. Compare might.
- The possibility use often implies less likelihood than
could. Compare
I can be cold in April
with
It may be cold in April
The former also implies in general whereas the latter often refers to a particular future. - The negative is slightly peculiar:
may not cannot express impossibility because there remains some doubt in the speaker's mind. We use can't/couldn't for that function:
That may not be his brother
(but it may be)
That can't/couldn't be his brother
(and I'm sure it isn't)
It does, however, express doubt in, e.g.:
That may not be what you need - may not for prohibition
(i.e., negative
permission) is used but
is very rarely contracted to mayn't. For example:
You may not leave until the examination time is up
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will |
| I will write when I can |
Essentially, will performs the following functions in English (see also the section on tenses, linked below, for the use of will to talk about the future):
| Function | Example |
| requests | Will you walk this way? |
| logical deduction | That will be the postman. |
| promise | I'll write when I can. |
| willingness / volition | Will you marry me? |
| insistence | He will keep complaining. |
| ability | The restaurant will seat 50 people |
| futurity | I will be 28 tomorrow |
Notes:
- The insistence use never contracts will to 'll.
So,
He'll keep complaining
is a prediction about the future but
He will keep complaining
is a comment on his insistence. - The promissory use is almost always only first person
unless we are reporting what someone else intended to do:
I'll come early to help
He said he'll write when he can
You said you'll do it
etc. - The negative of the use for deduction is
often formed with cannot:
That can't be the postman
but if the speaker is more certain or is basing the statement on evidence or experience then won't can be used:
That won't be the postman; it's too early. - The use for ability is somewhat formal and may be replaced by
the present simple tense. For example:
The bottle will hold 3 litres = The bottle holds three litres - There is often a confusion between volition and futurity which
is unhelpful for learners. For example:
Will you marry me?
refers to the hearer's present willingness or volition but
Will she marry him
asks for the hearer's speculation about the future.
See the guides to tense and aspect for more on this common confusion.
Arguably, will also functions as a tense-forming primary auxiliary verbs to which there is a guide linked below.
 |
shall |
| Shall we dance? |
Essentially, shall performs limited modal functions in English (see also the guide to tenses, linked below for the use of shall to talk about the future):
| Function | Example |
| suggestion/offer | Shall we go? Shall I help? |
| obligation | That shall not happen. |
| futurity | We shall be in France tomorrow |
Notes:
- The suggestion/offer use only occurs as an interrogative. This use is confined to the first person, singular or plural.
- The obligation function expresses great determination and is generally perceived as formal.
- In neither of the first two functions can the verb be contracted to 'll but it can, and usually is, contracted when it refers to futurity.
- The use of the verb to signal futurity is, in fact, a function of a primary auxiliary verb and that is how it is considered in the guide to them linked below.
 |
ought to |
| She ought to be on the train |
Essentially, ought to performs the following functions in English:
| Function | Example |
| obligation | You ought to go now. |
| logical deduction | She ought to be here around 6. (This could also imply obligation.) |
| advice | You ought to take him to the vet. |
Notes:
- The difference between strong advice and obligation is often very blurred (if it exists at all).
- It is often asserted that ought to implies a
sense of duty rather than pure
obligation
or advice. Compare:
You should write to him
with
You ought to write to him
For most learners of English, this is irrelevant.
(This distinction may stem from the fact that ought is an old past participle form of the verb owe and we owe a duty.) - The negative of ought to for obligation has two forms:
- No obligation: needn't / don't have to:
You needn't / don't have to go - Negative obligation: ought not:
You oughtn't (to) go.
Omitting the 'to' is rare and formal.
- No obligation: needn't / don't have to:
- The negative of the use for deduction is formed with cannot:
She can't have left already - There is some evidence of the existence of ought as a
non-modal auxiliary verb with forms such as:
You didn't ought to do that
Did he ought to ask permission?
etc.
Such forms are at best non-standard; many would consider them illiterate. - In American English in particular (but increasingly evident in
other standards) the bare infinitive is quite common in the negative:
You oughtn't do that
 |
had better |
| You had better not! |
This structure is not considered a central modal in all analyses
but it is included here because it acts like a central modal auxiliary verb in
many ways.
Essentially, had better performs the following functions in English:
| Function | Example |
| advice | You had better wear something warm on the boat trip. |
| warning / threat | You had better not do that again or there'll be trouble. |
| future (desperate) wishes | It had better rain soon or the garden will die. |
| suggestions | Hadn't we better ask for permission? |
Notes:
- The word had is frequently contracted to 'd, causing some to confuse it with
would. E.g.:
I'd better go = had better
I'd rather go = would rather - The form is only used for present or future events. There is no past
form and in reported speech the verb is often replaced, so
You had better not do it
is reported as:
He said we shouldn't do it
or remains unchanged
She told us we had better not be late - The negative form for advice is formed as had better not.
For example
We had better not be late - There is a common negative question form for
tentative suggestions:
Hadn't you better get some sleep? - The advice function only refers to
specific situations or actions. Compare:
You had better not listen to him
with
*You had better not listen to bad advice
For general situations or actions rather than specific ones, the preferred verb is should:
You should not listen to bad advice. - The warning / threat function is often implicit in the verb:
You had better not be late
may be responded to with
Or else?
The verb should does not routinely imply this. - The functions of hopes and warnings usually refer to a near future.
Hence the form is often accompanied by time adverbials such as
soon:
You had better finish that soon
He had better arrive in the next day or so or he'll be too late - The form is often used as an ersatz conditional:
You had better do that carefully or you'll get paint on the floor
equals
If you don't do that carefully, you'll get paint on the floor - Informally, better may be replaced with best:
You'd best tell the truth
Some consider this colloquial or even illiterate. - Question forms are as for other modal auxiliary verbs but are quite formal
and rarer:
Had I better talk to him?
In fact, the negative question form is a lot more common:
Hadn't I better talk to him? - The form is not used to talk about preferences (that's the function of would rather, see above under would).
- The form cannot be used for obligation although its use by someone in authority often implies obligation rather than advice..
- In rapid speech the 'd is often not audible and the form sounds like, e.g., you better, leading some to leave the word out deliberately in speech and in writing.
Summary
Here's a summary diagram of much (not all) of this. In
particular, restrictions are not included here.
The use of some verbs to signal futurity is distinguished here
in purple boxes because that function is that of a primary not modal auxiliary
verb.
 |
Other languages |
The concept of modality is common to all languages. We all have
a need to express things like willingness, probability, likelihood,
obligation, requirement and
so on. Modality may not only be achieved by the use of modal
auxiliary verbs, of course. Saying something like:
I'm almost certain
he'll be late
instead of
He'll be late
is still using
modality in language.
Modal auxiliary verbs are, however, very
variable across languages. Here's a brief run-down by major
language groupings explaining a little of how it all works. There
won't be enough detail here for your particular students and your
setting but it is somewhere to start. You can get more on line but
beware the unreliability of many sites.
Swan and Smith, 2001, is a usually reliable source albeit frustratingly
inconsistent in covering modality.
| Languages | What they do |
| Arabic |
Standard Arabic does not have modal
auxiliary verbs which correspond exactly to English modal auxiliaries. However, it does have many precise and detailed ways to express modal concepts. For example must, have to, should, might, may, it is possible to, it is impossible to, it is expected that, it is easy to, it is hard to, it's worth mentioning that, it's well-established that, it's most likely that, it's forbidden to, it's permitted to, it's more proper to and a range of other concepts are all expressed through a form of modal construction. The problem, of course, is that these categories do not mirror the modal categories of English so expect a good deal of confusion, especially with modal auxiliary verbs like may and could which have a range of functions. The concept of having a large range of modality in the language will not be mysterious to learners from an Arabic-speaking background. (Source: Arabic learning resources at http://arabic.desert-sky.net/g_modals.html) |
| Chinese languages | Modern Standard Chinese, too, has a
range of modal auxiliary verbs, as one would expect of an isolating
language. They are, however, not at all parallel to those
in English. There are, for example, three modal auxiliary verbs
which perform the functions associated with can (ability,
permission, possibility) in English. The most commonly
used modal auxiliaries in Chinese languages express want; ask for; wish; desire want to; would like to; feel like (something) should; ought to; must can; be able to; be capable of like; love; prefer; enjoy; be fond of can; may be good at; be skilful in be willing to Conceptually, modality poses no problems but overlapping meanings will make life difficult. |
| Slavonic languages including Russian, Polish, Ukrainian, Czech, Slovak etc. | Slavonic languages also have modal
auxiliary verbs but, as usual, the categories don't exactly match
(although they are closer than many languages). A single
verb form (roughly translatable as must) serves in
Polish for the English verbs must, need to and
ought to,
for example. In Czech, there is a clear distinction between externally and internally imposed obligations, often rendered in English by must vs. have to, should or ought to. Russian has a simpler modal system than English so you may encounter, e.g., He must not used to mean He needn't / doesn't have to. |
| Germanic languages | These languages use modality is ways
quite similar to English which makes life easier for learners
from these language backgrounds. The most important exceptions often
concern the negative uses. For example, in German the
translation of needn't / don't have to, expressing the
lack of obligation either way, would be must not
[muss nicht] and
that causes confusion. To translate the English sense of
must not meaning prohibition, German uses a different
modal auxiliary verb [darf nicht], roughly translatable as
may not. In Swedish, the verb used for the sense of needn't is cognate with the English expression behove. In these languages, too, there are usually more tense forms available so an equivalent of had to may be rendered as *musted. Learners may be confused by a logically constructed tense form in their first language, the past or future of must, for example, not existing in English. The overlap in meanings between cognate modal auxiliary verbs is not precise so expect errors such as It can be used to mean It might be. There are few serious conceptual difficulties otherwise. |
| Romance languages including French, Spanish, Italian, Portuguese, Romanian etc. | These languages do not have a separate
grammatical category for modal auxiliary verbs and usually render the
concepts as a verb followed by an infinitive form, e.g., in
French Je peux aller (I can go) or in Spanish Puedo
ir. Expect, therefore, errors such as *I can to eat *You must to enter etc. because many learners perceive the to-form as the infinitive in English. Some modal concepts, e.g., for obligation, are expressed in the passive (It is necessary that ...). There is, in these languages, no equivalent to the use of be to express obligation as in, e.g.: You are to be here at 6 and a modal auxiliary verb (often an impersonal one) will be used instead. |
| Swedish, Danish and Norwegian | Scandinavian languages have a separate
class of modal auxiliary verbs although use is an issue. The verb
kan, for example, is used to talk about the possible
future where English would use may or might.
Expect, therefore, *It can rain tomorrow. Other uses of modal auxiliaries are close parallels with English. |
| Japanese | Japanese has two classes of modal
auxiliary verbs: those which are attached to stems and cannot function
independently and those which are ordinary verbs which lose
their meanings when acting as auxiliaries. We have,
therefore, structures such as miru (to see) leading to
mirareru (to
be able to see). The concept of modality will not be strange but the forms will cause problems in English. |
| Greek, Turkish and other languages | Some languages have a very reduced set
of modal auxiliary verbs to call on. Greek, e.g., really has only two (must
and can), one of which only exists in the It is necessary
/ necessarily true that sense
in the third person. Added to these problems is the
tendency to make past modal auxiliary verbs in completely different ways (often
rendering the modal auxiliary in the present with the main verb in the past) so
mistakes such as *I can saw it (for I was able to see it) are possible. Turkish speakers will have few problems with the modal system of English as such because the language has many parallel structures if not always parallel senses. |
Try a test on all these modal auxiliary verbs.
| Related guides | |
| essential guide to modality | for a simpler guide in the initial training section |
| semi-modal auxiliary verbs | in guide which also considers marginal modal auxiliary verbs such as seem, tend, be about to etc. |
| types of modality | for a more technical (some say more useful) guide to types of modality such as epistemic and deontic modality |
| modal auxiliary verbs: tense and aspect | a guide which considers the modal auxiliary verbs in relation to perfect and progressive forms |
| primary auxiliary verbs | for the guide to how verbs function to form tenses and other aspects of the verb including passive clauses |
| complex tenses | a guide which considers complex tenses in relation to modality (I shouldn't have done it etc.) |
| multiple modalities | this guide considers how, despite the prohibition on co-occurrence, English manages to signal multiple modality |
| teaching modality | for some ideas on how to use this analysis which includes the consideration of other languages set out here |
| the modality index | for links to a range of related guides |