Permission/prohibition in other tenses

The gaps in the 'defective' verbs may and must [> 11.4, 11.6.1] can be filled with the verb phrases be allowed to and the more formal be permitted to. Examples of other tenses: present perfect: Mrs James is in hospital and hasn't been allowed

to have any visitors
past: We were allowed to stay up till 11 last night

Could can only express past 'permission in general'[compare > 11.12.1]: When we were children we could watch (or were allowed to watch) TV whenever we wanted to

11.25 Conditional sentences with 'could' and 'could have'

Could may imply 'would be allowed to':

/ could have an extra week's holiday if I asked for it

Could have + past participle can be used in place of would have

been allowed to to show that permission was given but not used:

You could have had an extra week's holiday You asked for it

I said you could have it, but you didn't take it [compare > 11.15]

11.26 'Can/could' = 'am/is/are free to': present or future

'Being free to' is often linked to the idea of 'having permission'. Can,

in the sense of 'am/is/are free to', can be used to refer to the present

or the future:
/ can see him now (= I am free to)

/ can see him tomorrow (= I am/will be free to)

Could expresses exactly the same idea, but is less definite:
/ could see him now (= I am free to)

/ could see him tomorrow (= I am/will be free to)

Compare can/could (= ability) which cannot be used to refer to the future [> 11.10, 11.16].

Uses of modals, etc. to express certainty and possibility

Certainty, possibility and deduction

If we are certain of our facts, we can make statements with be or any full verb [compare > 10.24]:

Jane is (or works) at home (a certain fact) If we are referring to possibility, we can use combinations of may might or could + verb:

Jane may/might/could be (or work ) at home (a possibility)

We may draw a distinction between the expression of possibility in this way (which allows for speculation and guessing) and deduction based on evidence. Deduction [> 11.32], often expressed with must be and can't be, suggests near-certainty: Jane s light is on She must be at home She can't be out

Modals, etc to express certainty/possibility

|1.28 Forms of tenses (certainty) versus modals (possibility)