3. müssen (to have to, must)
　　Present: Ich muss dort Deutsch sprechen. I have to speak German there.
　　Past/Preterite: Er musste es nicht tun. He didn't have to do it.
　　Pres. Perfect/Perfekt: Wir haben mit der Bahn fahren müssen. We had to go by train.
　　Future/Futur: Sie wird morgen abfahren müssen. She will have to depart tomorrow.
　　Subjunctive/Konjunktiv: Wenn ich müsste... If I had to...
　　NOTE: For all modals with umlauts, the simple past (preterite/Imperfekt) has no umlaut, but the subjunctive form always has an umlaut!
　　Sample Idiomatic Expressions:
　　Ich muss nach Hause. I have to go home.
　　Muss das sein? Is that really necessary?
　　So müsste es immer sein. That's how it should be all the time.