Modal Verbs

General information
Modal verbs: must can could may might should shall would will ought to

Ability I
(present and past)

Ability I
(present and past)
To emphasis difficulty or to suggest effort, we use manage to/succeed in +ing. Do you think she will manage to get a visa?
If the future arrangement is less certain we use could, may or might +be able to. The dentist might be able to see you late today; I’ll have to check my diary.

Ability II
(past)

Ability II
(past)
Could have +P II to describe the past ability which wasn’t used or past opportunity which wasn’t taken. She could have paid by credit card but she preferred to use cash.
Couldn’t have been+ comparative adj to emphasise a past action or feeling. I couldn’t have been more pleased when I heard your result.

Possibility
Present
can – when we talk about things which are generally possible. May - academic or scientific English. Healthy insurance can be very expensive. Over-prescribing of antibiotics may lead to the rapid development of resistant strains.
May/might/could – specific possibility. This rash could be a symptom of something more serious.
May well/might well/ could well – to talk about a strong possibility. Don’t worry! The payment may well be in the post.

Possibility
Present
Could/might – possibility which depends on certain condition. She could learn much more quickly if she paid attention.
POSSIBLY NOT – may not/might not
DEFINITLY NOT – can’t.

Possibility
(future)
Will/won’t be able to – talk about future possibility or impossibility. We’ll be able to get a coffee at the theatre but we won’t be able to eat until after the show.
May/might/could – talk about future actions which are less certain (perhaps)
Could – for possibility weaker than may/might.
Couldn’t – is not used to say something is definitely impossible (present\future).
May/might have+P II – possible completed action by the time in the future. Call me tomorrow. I might have finished the project by then.