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Concourse 2

Modality: tense and aspect


Before you tackle this guide, you should be confident that you are familiar with the contents of the essential guide to modality and the guide to central modal auxiliary verbs.
You should also, of course, be familiar with the distinctions between time, tense and aspect.
All those links open in new tabs.



Pure or central English modal auxiliary verbs are often described as defective, meaning that they cannot be used with the full range of inflexions or in the full range of tenses and aspects that lexical or main verbs allow.
For example,
smoke, go, enjoy, imagine, come, decide, think, spin etc. are all non-defective, lexical or main verbs and change form to show:

Modal auxiliary verbs cannot be treated this way (*I musted, *He musts, *I am musting, *They have should etc.)

Unlike many languages, English has few natural past-tense forms for modal auxiliary verbs.  There is, for example, no simple past-tense way of expressing
    I must go now
If we want to put it in the past, we are obliged to use somewhat clumsy formulations such as
    I had to go then
    He said he had to go then
    I was obliged to go then

and so on.
Equally, when we use reported or indirect speech, we are often forced to substitute modal auxiliary verbs with other expressions and report, for example:
    You may go
    He gave me permission to leave
    He said I might go
is another possibility.
See the guide to reported speech, linked below in the list of related guides, for more on how we cope with the difficulty of reporting modal expressions like these.

Here's the list of modal auxiliary verbs showing which do and which do not have past-tense forms.  We have included some cases of marginal modal auxiliary verbs and semi-modal auxiliary verbs in the grey rows.

Present Past
can could
may could / might
shall should
will would
must (had to)
---- used to
had better ----
ought to ----
need ----
dare dared

The verb had to is shown in brackets because it is actually non-defective and can be altered for tense and person:
    She has to go
and for aspect
    She's having to work long hours
    She has had to work long hours
    She will have to work long hours
The formulation of the copula plus the adjective able is similar although it does not permit the progressive participle.  We can have:
    He was able to open the case
    We had been able to open the case
    He will have been able to open the case

but not
    *He was being able to open the case
or any other progressive, continuous, iterative or durative -ing form.
Other languages are more obliging and have forms of modal auxiliary verbs or modal expressions akin to canned, musted etc. to express past obligation or past ability or will must, will can to express future ideas.

To complicate matters, although some modal auxiliary verbs have past forms (see above) there are restrictions on meaning when they are used that way.
For example, the past form of may is might when used in indirect speech so:
    She said, "I may go out later"
can be reported as:
    She said she might go out later
However, there is no simple past form of:
    I may see my mother today
    *I might see my mother yesterday
is not available as a past tense.  There is also a present form which looks like it:
    I might see my mother today
which has a different meaning, expressing slightly less certainty.
Equally, although
    You can leave, if you like
is used to signal present permission, the past form:
    You could go, if you like
is not its past tense because it expresses the same idea and remains a present form.

This is not to say, of course, that English is incapable of expressing the ideas of tense and aspect with modal auxiliary verbs.  However, the ways it is done are often complicated and difficult to learn.  For example:

Past permission and prohibition: I was allowed / permitted to ...
I could ...
It was forbidden to ...
    *I can have helped
is not available as the past of
    I can help.
Past ability: I was able to ...
I could ...
I had the ability to ...
    *She can have climbed the wall
is not an available option as a past form of
    She can climb the wall.
Past volition: He said he was willing to ...
She was happy to ...
He said he would help
The past of the volitional use of
    I'll make the dinner
is not available as
    He said he'll have made the dinner
because that carries a future perfect meaning.
The past form would is an available option which occurs in contingent (conditional) clauses but often without the sense of volition except in indirect speech.

In summary, past ability, past permission and past volition are not normally expressed using a perfective aspect.


Prospective events

Many modal auxiliary verbs are, so to speak, tensed already for a prospective aspect.

The future in English is often expressed via a modal auxiliary verb because the future is, by its nature, uncertain in a way that the past is not.  Many modal auxiliary verbs refer to the future without any marking to show the tense.  That's why, for example all the following can refer to the future:
    She could come here
    They may be leaving
    I might ask a question
    I must be there
    I can see her
    We ought to go
    I have to work

and so on.
Into all those sentences we can insert a simple time adverbial, such as tomorrow, later, soon etc. and the sentences immediately and unequivocally refer to future time with, importantly, no change to the syntax or form of the verbs.  The modal auxiliary will when it is used to refer to the future (rather than present willingness) is no different in this respect.


Which modal ideas can be used with aspects?

Some types of modality can be expressed using an aspect of the modal auxiliary verbs.  For example, we can say:

Perfective aspect: She will have missed the train
She might / could have missed the train
She can't have missed the train
He shouldn't have said that
He needn't have gone
She can't have arrived yet
Progressive aspect: She must be getting tired
They might be arriving late
I may be travelling for work
You can't still be working
He shouldn't be smoking
He can't be working at this hour
You should be working less
Combined perfective and progressive aspects: She must have been getting tired
She shouldn't have been working so long
They can't have been working hard enough
They shouldn't have been playing by the river
They might have been arguing
They oughtn't to have been sleeping

For more on the distinction between perfect aspect (i.e., a relational tense form) and perfective aspect (i.e., a finished, absolute sense) see the guide to time, tense and aspect, linked below.
Here, it is enough to point out that although the form of, for example:
    She could have left her keys in the office
appears to be a perfect aspect akin to:
    She has left her keys in the office
there is a key difference.
When a modal auxiliary verb is used in the past to express a past idea, it is perfective (i.e., done with, finished and completed).
When a main verb is used that way, the sense is very different because the perfect aspect serves to embed the past in the present and alter it in some way.
The usual completion of the example above is, therefore, something like:
    She has left her keys in the office so can't get in to her flat.
showing that the past event has altered the present.  That's why, on this site, the form is referred to as the past in the present.
This is not the case when the same form is used with a modal auxiliary verb so:
    She must have left her keys in the office
has no implicit sense of the past event affecting the present.  It refers, merely, to the speaker's attitude concerning the likelihood of the proposition being true.  In that sense, it is parallel to the simple past form of:
    She left her keys in the office
which also implies no present-time consequence.


Identifying types of modality

The trick, of course, is to identify the types of modality that can be used in this way and those that can't.  To do that, we need a little logical theory.

speculation and deduction
this is called epistemic modality because it refers to the speaker's viewpoint regarding the truth or otherwise of a proposition based on the evidence available.  From the table above, these are examples of epistemic modality, expressing various degrees of confidence:
    She will have missed the train
    She might / could have missed the train
    She can't have missed the train
    She can't have arrived yet
    She must be getting tired
    They might be arriving late
    I may be travelling for work
    You can't still be working
    He can't be working at this hour
    She must have been getting tired
    They can't have been working hard enough
    They might have been arguing
degrees of obligation
this is called deontic modality because it concerned with duty or obligation (or the lack thereof).  From the table, these are examples of deontic modality expressing varying degrees of obligation:
    He shouldn't have said that
    He needn't have gone
    He shouldn't be smoking
    You should be working less
    She shouldn't have been working so long
    They shouldn't have been playing by the river
    They oughtn't to have been sleeping

There are two other types of modality which do not normally occur with the perfective, progressive or perfect aspects:

  1. alethic modality
    This refers to truth of propositions in the sense that something is necessarily rather than deductively the case.  For example:
        Iron must be heated to 1,538°C to melt
    This cannot be referred to as
        *Iron must have been heated to 1,538°C to melt
    because it is a necessary (i.e., always true) property of the element.
  2. dynamic modality
    This refers to modality centred on the subject.  For example:
        I can see the mountains
    is not to do with external obligations, duties or a view of the truth of a proposition.  We can have, e.g.:
        I could have swum across the river
    but only in the sense of an unfulfilled ability.  If we say, e.g.,
        She could have swum across the river
    the hearer will understand that we are referring to a possible event (i.e., epistemic modality), not a past ability.  For past ability, we would use the past tense of can and have:
        She could swim across the river
    or the replacement form
        She was able to swim across the river

For more on the types of modality referred to here, see the guide to types of modality, linked in the list of related guides at the end.

The point bears repeating that, although the forms parallel the forms of the perfect aspects used with main verbs, the sense of two events being relational is not maintained with modal auxiliary verbs.  So, for example:
    She might have arrived late
refers to the speaker's view that an event was (not has been) possible.  It is not parallel to:
    She has arrived late
because the reference is to a completed possible past action, not a past event which changes the present.
It is, however, the way in which speakers signal that they doubt the truth of the proposition concerning the finished past event:
    She arrived late
There is more on this distinction to follow.


Perfect and perfective aspects

It is important to understand what the modal auxiliary verb + have + past participle is actually implying in terms of aspect.
If you have followed the guide to aspect on this site, you will be aware that the view taken here is that a sentence such as
    He has arrived
is actually a present tense form with a perfect aspect.  In other words, the have + participle form refers to the present in relation to the past.  Another way of putting that is to say that it is the past embedded in the present.  The present perfect is a relational, present tense.

Unfortunately, when we are dealing with modal concepts, that definition of the function of the structure is only partially true.  Here are some examples to explain:

Example Explanation
She might have missed the train and still be at the station This is a true perfect aspect of the verb phrase because it refers to the present in relation to the past.
He shouldn't have said that and upset her so This is, in fact, a perfective past form.  Both the saying and the upsetting refer to events and states in the past.  We can add a fixed time phrase such as last week to this sentence and we cannot do that conventionally with a present perfect form.
He needn't have gone but he did This is another perfective past form.  The lack of obligation and the going are both in the past and may or may not have any relation to the present.
She can't have arrived yet This is a perfect aspect referring to the temporal relationship between an event and a current state.  The non-arrival (up to now) relates to the fact (in the present) that she is not here.
She could have arrived before me The use of could in this sense is perfective when we are referring to ability or possibility.  We may, in fact, be talking about events far in the past which bear no relation at all to the present.
She must have been getting tired and probably fell asleep Here we have another perfect aspect but one which relates a past event to a previous past state.  It is parallelled by, e.g., She had got tired and fell asleep.

In summary, the general distinction between relational tense forms (perfect aspect) and absolute tense forms (simple aspect) breaks down when modality is considered.
This is a key teaching point because the rule of present relevance signalled by the have + participle form no longer consistently applies.
For more on the distinction between relational and absolute tenses in English, see the guide to time, tense and aspect, linked below.

progressive etc.

Progressive and other aspects

Reassuringly, even with modal auxiliary verbs, the distinctive uses of the be + -ing formulation remain intact.  Here are some examples:

Example Explanation
She must be getting tired This is a continuous aspect, referring to a state rather than an event.
They might be arriving late This is a prospective aspect referring to a future based on present data.
I may be travelling for work This is an iterative sense referring to a repeated (but not current) action.
You can't still be working This is a true progressive aspect referring to an action in progress.
He shouldn't be smoking This is a habitual aspect referring to a current routine.


Passive constructions

Passive constructions are available in English for all types of modality and for both aspects.  For example:

Example Explanation
This must be reprinted This is the passive present infinitive and is the most commonly used.
Its use is not, however, confined to modal auxiliary verbs.
The house should have been finished by then Passive perfective but used for both past and future with a change in the types of modality:
Epistemic modality:
    I am speculating that the house is in fact finished.
The implication is that I am speaking about the future in relation to what came before it (compare the greater certainty of
    The house will have been finished by then).
Deontic modality:
    I am stating that there is or was an obligation of some kind that the house was finished.
The implication is that the house is not in fact finished.
The house might have been finished This is epistemic modality only.  It is speculation about the present state of the house.
The house should be being finished Like the first example, this can be speculation concerning what is currently taking place (epistemic modality) or implying an obligation that work is being done on the house now (deontic modality).
The house may be being finished This is epistemic modality only.  It is speculation about the present state of work on the house.  It can be replaced with could with little or no change in meaning.  In this case, could is only speculative (epistemic) and not to do with ability (which would be dynamic modality).
The house should have been being finished This is a combination of the passive with both a progressive and perfect aspect and is quite unusual.  It is an available construction in English (and should is replaceable a range of other modal auxiliary verbs to make different types of modality).  Some consider it clumsy at best, wrong at worst.

There is more on passive infinitives in the guide to the passive, linked below.


An example with should of tenses and aspects with modal auxiliary verbs

She should write it down  

Here is a set of examples with an identification of the tense, aspect and voice being used with modal auxiliary verbs usually concerned with deontic or epistemic modality.
In most cases, other deontic modal expressions can be used and examples of these appear in the fourth column.
The same applies to epistemic modality, of course, but no examples are given for that here.  Make them up if you like.

Deontic modality Examples Description of form Alternatives Epistemic modality
Concerning the present or the immediate future Shouldn't you go to bed?
You should work less
Present infinitive My advice is to go to bed
It would be better if you worked less
Could he be upstairs?
Concerning the present or the immediate future Should you be helping Mary?
Shouldn't you be studying this evening
Present progressive infinitive It is your duty to help Mary
Isn't there an obligation on you to study this evening?
Could he be working in his room?
Concerning the present, timeless habits or the immediate future This shouldn't be left here
That should be written again
Present passive infinitive This is the wrong place for it
It is necessary to re-write this
This could be the wrong place for this
Commenting about the past She shouldn't have done that
I should have left earlier
Perfect infinitive It was unwise of her to have done that
It would have been better if I had left earlier
She mightn't have done that
Commenting about the past I shouldn't have been working so late
They should have been training
Perfect progressive infinitive It was unwise to have been working so late
There was an obligation on them to train
I may not have been working
Commenting about the past That letter should have been better proofread
She shouldn't have been asked to do that
Perfect passive infinitive There was a need to proofread that letter
It was unwise to have asked them to do that
The letter may have been better proofread
Commenting about the past (relevant to the present) The car should have been being serviced
The house should have been being lived in by now
Perfect progressive passive infinitive It was necessary that the car had been being serviced
The house needed to be ready to be lived in by now
The car might have been being serviced

There are those for whom the examples in the last row are clumsy but the forms are available, and sometimes heard or read.


Teaching in this area

There is ample scope for confusion in this so things have to be taken carefully.  A first rule of teaching is not to overload learners and a second is to distinguish very carefully between the types of modality which can be used with the perfect or perfective forms.
It is, of course, not necessary to burden learners with terms such as epistemic modality but, in order to be clear and helpful, teachers need to be aware of the meaning of the terms and select targets and settings in which the modality is clear.

The final important thing to note is that the form which appears to be a perfect aspect, e.g.:
    I might have told him
is, in fact, often perfective (i.e., finished and fixed in time) and unrelated to the perfect aspect of, e.g.:
    I have told him
which refers to the fact that he currently knows whatever it is.
The distinction can be made clear with the addition of an adverbial which is allowable in:
    I might have told him last Thursday
but disallowed in:
    *I have told him last Thursday
This is not at all easy to grasp.  Learners who have taken pains to assimilate the concept of the relational nature of perfect aspects may be bewildered to discover that it no longer applies in many cases.


Teaching ideas

If you refer to the guide to teaching modality, linked below, you will find a number of teaching ideas evaluated in terms of their clarity and efficacy.  The key point is to distinguish the type of modality which is being considered.  Mixing them up will cause a good deal of confusion, not least because some of your learners' first languages may reserve particular verbs or structures for each type of modality.

for epistemic modality
Deductive procedures such as the ones outlined in the guide to teaching modality are fruitful providing the level of (un)certainty is clearly identified.
For future time, speculation exercises are common and science fiction can be an engaging focus.  Topics typically include:
    What do you think your home town will be like in 20 years' time?
    What technology do you think will be available to your grandchildren?
    What do you believe cities of the future will be like?

Younger students can be encouraged to think about their own futures.
All these questions contain a verb process realised by verbs like think or believe.  That's important or the response will simple be a future perfect form expressing too much certainty.
However, as is the case for deduction settings, the degree of certainty signalled by the modal auxiliary verbs and intonation / stressing is a key consideration.
In the past, epistemic modality (e.g., for deduction based on current evidence) can be practised with the use of accident- or crime-scene graphics to elicit, for example:
    The burglar must have come in through the bathroom window
    The driver of the red van can't have been looking
    He might not have indicated
    He must have been in the bedroom

If you would like to download a lesson using the crime-scene idea at B2/C1 level, click here (new tab).
for deontic modality
The telling of a story containing many instances of poor judgement calls is an engaging procedure.  For example, the following story read aloud quite slowly with pauses to allow interruption using shouldn't have ... can work well:

When I landed at Heathrow, I left my coat on the plane because I knew it's always warm in London.  After that, the first thing I did was light a cigar and take a few photographs of the arrivals hall.  When my turn came to have my passport checked I refused to hand it over and told the woman she looked silly in her uniform.  Before I left the airport I decided to leave my luggage behind in an airport café because it was too heavy to carry and then I started to walk to central London.

The types of responses one hopes for are, e.g.:
    You shouldn't have done that; you should have ...
This can be combined later with expressions of epistemic modality along the lines of:
    You shouldn't have done that because she might have got very angry
Learners can be further engaged by getting them to write their own silly stories and reading them out for others to comment on.  Possible topics are:
    A disastrous holiday choice
    A dreadful dinner party with the wrong guests sitting together


Related guides and links
essential guide to modality a simpler guide in the initial training section
central modal auxiliary verbs a traditional view taking each modal in turn and identifying its function
semi-modal auxiliary verbs a guide which also considers marginal modal auxiliary verbs such as seem, tend, be about to etc. alongside the true semi-modal auxiliary verbs, need, dare, used to
time, tense and aspect this is the place to go if the distinctions between, e.g., perfect and perfective, continuous and progressive are obscure
the passive for more on the use of modal auxiliary verbs in the passive voice and with the infinitive
complex tenses which also considers complex tenses in relation to modality
teaching modality for some more ideas transferable to the analysis above
types of modality for more on types of modality mentioned here such as epistemic and deontic
the modality map for a clickable map to the guides in this section
modality index for links to guides to other areas of modality