Modal verbs, module 4

New notions:
Possibility
Ability
Permission
Obligation
Request
Necessity
Advice

Main meanings
Must – obligation imposed by the speaker / logical assumption
Have to – obligation imposed by a situation (external obligation)
Ought to – moral obligation denoting a duty, advice or a reasonable action
Need to – necessity
Should – suggestion, advice
Can – possibility, ability, permission
Could – past possibility, ability, asking for permission
May – request, permission
Might – possibility (higher degree of doubt), polite suggestion