Breakdown of Die Explosion, deren Grund geheim ist, war gefährlich.
sein
to be
gefährlich
dangerous
der Grund
the reason
der
who, which, that (relative pronoun; die, das)
Questions & Answers about Die Explosion, deren Grund geheim ist, war gefährlich.
Why do we use deren here instead of dessen?
deren is the genitive relative pronoun meaning 'whose'. It refers back to the feminine noun die Explosion. In German, genitive relative pronouns always match the gender and number of the 'owner' (the explosion), not the thing being owned (der Grund).
How does the noun Grund in this sentence relate to the preposition aufgrund?
The preposition aufgrund (because of / due to) is actually built directly from the noun der Grund (the reason / the ground). While your current lesson focuses on the preposition aufgrund, this sentence shows the core noun itself being used to talk about the 'reason' for the explosion.
Why does the verb war immediately follow the second comma?
The main sentence is simply Die Explosion war gefährlich. The relative clause (deren Grund geheim ist) is just inserted into the middle of it to add extra information. Once that relative clause finishes, the main clause picks up exactly where it left off with its verb (war).
Why is the verb ist at the very end of the middle section?
The phrase deren Grund geheim ist is a relative clause, which acts as a subordinate clause. A major rule in German grammar is that subordinate clauses always kick the conjugated verb (ist) to the very end of their specific clause.