The modal verb sollen

 

The modal verb sollen expresses a necessity that is the result of a request/command addressed to the verb's subject by a third party.

 

Examples request/command addressed to the subject:
Ich soll einkaufen gehen. Meine Mutter sagte zu mir: "Geh einkaufen!"
Ich soll Sport treiben. Mein Arzt sagte zu mir: "Treib Sport!"

 

This request/command can derive not only from a person but also from something abstract, like social norms. In this case, it expresses a necessity that is attributed to moral duty or regulations.

 

Examples request/command addressed to the subject as
Du sollst ehrlich sein. a moral duty
Man soll seinen Hund an der Leine führen. regulation