Müssen
means to have to (or to must). There is a similar modal
verb sollen = to shall. Anyway, müssen is much
stronger and describes situations of no alternative
or some kind of "force".
müssen
to express that there is no alternative
The fact
that there is no alternative may result from
a logical consequence, the law or a natural
force.
Wir
müssen das Auto stehen lassen, die Kupplung
ist kaputt.
= We have to leave the car, the clutch is
broken.
Wer
eine Bank ausraubt, muss ins Gefängnis.
= The one robbing a bank has to go to prison.
Ein
Stein, den man gen Himmel wirft, muss auf
die Erde zurückfallen.
= A stone that is thrown towards the sky must
fall back to earth.
müssen
to express doubts
In conjunctive
II the verb müssen can be used to express
doubts. In English the translation is then
the conjunctive of shall.
Er
müsste es wissen.
= He should know.
Usually
müssen is not used to imply any freedom
of choice. In spoken language it is nowadays
very common to emphasise the importance of
something with müssen:
Dieser
Film ist genial, den musst du dir anschauen.
= The movie is great, you have to see it.