Modal verbs of obligation, prohibition, advice and permission

We use ____________________ and ____________________ ____________________ for obligatio n

____________________ and ____________________ ( must not ) are used to show that something is prohibited ( not allowed ) .
____________________ is most often used to ask for or give permission .

We use ____________________ ____________________ ____________________ to show that there is no obligation . You can do something if you want but it is not an obligation .

English speakers use the modal verbs ____________________ and ____________________ ____________________ , to express that they think something is a good ( or a bad ) idea .
____________________ ____________________ is a bit stronger . It includes the idea of a warning : something bad will happen if you do not follow my advice .