German Grammar Explained /
Subjective meaning of "dürfen"
Modal verbs can also have a subjective meaning when the speaker tries to imply something in an indirect way - something that is very German ;)
The modal verb dürfen (to be allowed) can be used to express something that we think is quite likely but we are not quite sure about. For example, if you are 75% sure that something is true.
Another way to emphasize this uncertainty is to use adverbs such as wahrscheinlich (probably) and vermutlich (presumably).
Dürfen with a subjective meaning is always used in the subjunctive II form.
Kerstin dürfte nicht zu spät kommen.
Kerstin probably won't come too late.
→ Kerstin ist rechtzeitig losgegangen und wird wahrscheinlich pünktlich beim Meeting sein. Kerstin left with plenty of time and she is probably going to make it on time her meeting.
Die Supermärkte dürften heute sehr voll sein.
→ Da die Supermärkte morgen geschlossen sind, sind sie heute wahrscheinlich sehr voll. Because the supermarket is closed tomorrow, it is probably going to be very full today