Modals

Modals
can, be able to, could, may, might, must, have to, need to, don't have to, should, ought to, had better, will, shall, needn't

Synonyms
manage to (ability)
be allowed to / allow to (permission)

Characteristics
- 3rd person singular without -s
- after a modal: infinitive without to
- questions without do
- no -ing (no progressive form)
- they don't have all the tenses
    can: only present
    could: only past, conditional
    must: only present
    have to: present, past, future

Obligation
Present: have to, must, need to
Past: had to, needed to

No obligation
Present: don't have to, don't need to, needn't
Past: didn't have to, didn't need to

Permission
can, may, could, be allowed to / allow to
(formal: may, could)

Advice
should, ought to, had better

Ability
can, could, be able to, manage to

Possibility
can, could, be able to

Deduction
must, may, might, can't
(nowadays synonyms: may, might)

Prohibition
musstn't, not allow to / not be allowed to

Suggestions and offers
shall

Requests
will, can, could


be able to forms
Present: I am able to ...
Past: I was able to ...
Future: I'll be able to ...
Present Perfect: I have been able to ...
Infinitive: I'd like to be able to ...
Gerund: I love being able to ...
Going to: I'm going to be able to ...