Breakdown of Jeder Briefumschlag wurde damals von den Schülern versiegelt.
von
from, of / by (agent in passive clauses)
damals
back then
jeder
everyone / each
der Schüler
the pupil, the school student
Questions & Answers about Jeder Briefumschlag wurde damals von den Schülern versiegelt.
If this sentence is reporting a past event, how does the word damals relate to what the original speaker actually said?
This is a great example of shifting perspective in reported speech. The original speaker describing the rule probably used a present-tense time marker like heute (today) or jetzt (now), for example: "Jeder Briefumschlag wird heute versiegelt." When you report that statement later, the perspective shifts, and heute changes to damals (back then) or an jenem Tag (on that day).
Why do we use von den Schülern instead of durch die Schüler for "by the students"?
In German passive sentences, von (followed by the dative case) is used for the "agent"—the person, animal, or active force intentionally performing the action. durch (followed by the accusative case) is used for a means, instrument, or cause. Since the students are the people actively doing the sealing, we use von.
Why is it Jeder Briefumschlag (nominative) instead of Jeden Briefumschlag (accusative) if the envelope is having something done to it?
In an active sentence, the envelope would indeed be the direct object in the accusative case (e.g., "Die Schüler versiegeln jeden Briefumschlag"). But this is a passive sentence. In the passive voice, the object receiving the action becomes the grammatical subject of the sentence. Subjects always take the nominative case, which gives us jeder Briefumschlag.
Could I use the Perfekt passive (ist ... versiegelt worden) instead of the Präteritum (wurde ... versiegelt)?