oxford_guide_to_english_grammar

12 MODAL VERBS PAGE 120
Here could means a more distant possibility than can and so is less direct, more
tentative. May is rather formal.
NOTE
We can also use might to ask permission, but it is both formal and tentative.
I was wondering if I might borrow your car for the afternoon.
3 Talking about permission
a
b
c
d
We sometimes talk about permission when we are not giving it or asking for it. To
do this, we can use can referring to the present or the future and could referring to
the past.
I can stay up as late as I like. My parents don't mind.
These yellow lines mean that you can't park here.
At one time anyone could go and live in the USA.
We cannot use may here because we are not giving or asking permission.
NOT I may stay up late.
We can also use be allowed to.
I'm allowed to stay up as late as I like.
Was Tina allowed to leave work early?
You won't be allowed to take photos.
Be allowed to means that the permission does not depend on the speaker or the
person spoken to. Compare these two sentences.
May we leave early, please? (= Will you allow it?)
Are we allowed to leave early? (= Is it allowed?/What is the rule?)
We use be allowed to (not can or may) in the perfect and the infinitive.
Newspapers have not been allowed to report what is going on.
I didn't expect to be allowed to look round the factory.
In the past, we make a difference between general permission and permission
which resulted in an action. For general permission we use could or was/were
allowed to.
Years ago visitors to Stonehenge could go/were allowed to go right up to the
stones.
For an action that someone did with permission, we use was/were allowed to.
The five students were allowed to go right up to the stones.
95 Certainty: will, must and can't
1 We can use these verbs to say that something is certainly true or untrue.
There's someone at the door. ~ It'll be the milkman.
You got up at four o'clock! Well, you must be tired.
This can't be Roland's textbook. He doesn't do physics.
Will expresses a prediction. It means that something is certainly true, even though
we cannot see that it is true. Must means that the speaker sees something as
necessarily and logically true. Can't means that the speaker sees it as logically
impossible for something to be true.
Must and can't are opposites.
The bill can't be so much. There must be some mistake.