You know modal verbs for ability, permission, and obligation. B1 reveals a second, 'subjective' use: the same modal verbs can express how CERTAIN you are about something — a guess, not a fact.
Types you should know
müssen (Vermutung)
must be — near certainty
können (Vermutung)
could be — possibility
dürfte (Vermutung)
is probably — confident guess
See it in action
German
English
Er muss zu Hause sein. (sein Auto steht davor)
He must be home. (his car is out front — near certainty)
Sie kann noch im Büro sein.
She could still be at the office. (possibility)
Das dürfte stimmen.
That's probably right. (confident guess)
Memory trick: Compare the two meanings side by side: 'Ich muss arbeiten' (obligation: I have to work) vs 'Er muss im Büro sein' (assumption: he must be, based on evidence) — same word, totally different job.
⚠ Common mistake: Don't confuse this assumption use with the basic obligation meaning — context (and often a piece of evidence mentioned nearby) tells you which one is meant.
🎯 Quick check
'Sein Licht ist an. Er ___ zu Hause sein.' Which modal verb best expresses a confident guess?