if+present simple, will+infinitive
if+past simple, would+infinitive
if+past perfect, would have+past participle
Pronom+modal verb+have+past participle
Pronom+modal verb+not+have+p. P.
Modal verb+pronom+have+p. P.+?
Permission (can/be allowed to)
Ability (can/could/be able to/managed to)
Obligation (must/have to/need to)
No obligation (don't have to/needn't)