The labels we use to describe the verb tenses (e.g. present, progressive, past, perfect) cannot easily be applied to modals.
11.8.1 'Present'
All modals can refer to the immediate present or the future, therefore
'present' is not always a reliable label:
/ can/may (etc.) phone now I can/may (etc.) phone tomorrow
General characteristics of modal verbs
11.8.2 'Progressive'
There is no progressive form for modals. But we can put the verb that
follows a modal into the progressive form:
Meg is phoning her fiance (present progressive
Meg may be phoning her fiance (modal + be + verb-ing
Meg may have been phoning her fiance (modal + have been+ing
It is the phoning that is or was in progress, not 'may'.
11.8.3 'Past'
Would, could, might and should can be said to be past in form but
this usually has little to do with their use and meaning. They can be
called 'past' when used in indirect speech [> 15.13n6]:
He says you can/will/may leave early (present)
He said you could/would/might leave early (past)
Might can have a past reference in historical narrative:
In the 14th century a peasant might have the right to graze pigs on
common land However, might usually expresses more uncertainty than may.
I might see you tomorrow is less certain than:
/ may see you tomorrow
Could sometimes expresses ability in the past [> 11.2.1]:
He could (or was able to) swim five miles when he was a boy but could is not possible in:
/ managed to/was able to finish the job yesterday. [> 11.12.3] However, couldn't and wasn't able to are usually interchangeable
/ couldn't/wasn't able to finish the job yesterday The other main use of could, as a more polite alternative to can in requests, has nothing to do with time:
Could you help me please?
Would expresses the past in [> 11.61]:
When we were young we would spend our holidays in Brighton Otherwise, would and should have special uses [e.g. > 11.74-75
Must can express past time only in indirect speech [> 15.I3n6].
otherwise it has to be replaced by have to, etc. [> 11.4]: He told us we must wait (or we had to wait) until we were called She asked her boss if she must work (or had to work) overtime
11.8.4 'Perfect' and 'past'
Forms with modal + have + past participle or with modal + have been + progressive are not necessarily the equivalent of the Present perfect. The modal refers to the present, while have + past participle refers to the past. So, depending on context,
You must have seen him can mean:
/ assume (now) you have seen him (i.e. before now; equivaent to
the present perfect)
/ assume (now) you saw him (i.e. then; equivalent to the past)
/ assume (now) you had seen him (i.e. before then; equivalent to
the past perfect)
11 Modal auxiliaries and related verbs
11.9 Modal + verb and modal + 'be/have been' + progressive
Two observations need to be made here:
1 Modal + be/have been + progressive is not always possible in the
primary function. For example:
He can't leave yet (= it's not possible for him to leave yet) is quite different from the secondary function: He can't be leaving yet (= I don't think he is) But compare the primary and secondary functions of must in: primary: You must be working when the inspector comes in
(i.e. it is necessary (for you) to be working.) secondary: You must be joking'
(i.e. I'm almost certain you are joking.)
2 Occasionally, in the primary function, a modal + be + progressive
has a 'softening effect' similar to the use of the future progressive
[> 9.41.2]. So:
We must/may/should (etc.) be leaving soon is more polite and tentative than: We must/may/should (etc.) leave soon