CAN - Permission (informal)
HAVE TO - obligation (external)
MUSTN'T - prohibition
MUST - obligation (personal)
MAY - possibility
CAN - possibility
MUST - deduction
DON'T HAVE TO - no obligation
CAN - ability
MAY - permission (formal)
Can I make a phone call?
You mustn't leave the school jumping over the fence.
"May I come in?" I asked the headmaster.
Passengers have to hold their passports when passing the police control.
Passengers must check that they have their luggage.
You can't be on time, the bus left ten minutes ago
Walter can check his emails when he is cooking
If your car is correctly parked, you don't have to worry.
I am busy all day but I may lend you a hand after work.
Eddie's twin brother must be the one on the left because they look alike.