What is a modal verb?

Modal verbs – Modalverben – are a special group of verbs.

Use them to say:

what you must domüssento have to, must
what you are able to dokönnento be able to, can
what you want to dowollento want (to)
what you are supposed to do/what you should do/what you ought to do (It often means 'shall', eg shall/should I help you?) sollento be supposed to, ought, should
what you may do/what you are allowed to dodürfento be allowed to, may
what you likemögento like