Modal verbs (hulpwerkwoorden)
Can: OK? (mogen) = permission
Can you stay up late? (Is it OK?)
I can stay up late at the weekends. (It's OK.)
I can't stay up late during the week. (It isn't OK.)
Have to: necessary? (moeten) = obligation
Do I have to go to bed? (Is it necessary?)
You have to go to bed. (It's necessary.)
You don't have to go to bed now. (It isn't necessary.) (hoeft niet)