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