"Hans is Karl's brother."
Translation:Hans ist der Bruder von Karl.
But why "the"? I'd say "Hans is a brother of Karl" (if I avoided saying "Hans is Karl's brother" for some reason) , not "the brother". Or do you have to use a definite article here in German?
My point was that I think "Hans ist ein Bruder von Karl" should also be correct, what do you think about it?
Ah, sorry, I just missed the "a". I'm not sure about that. "Hans ist Karls Bruder" (just like "Hans is Karl's brother") makes me think that Karl has only one brother, while "ein Bruder" would be only one of several brothers.
Apart from that, "Hans ist ein Bruder von Karl" is a correct German sentence.
I understand why DER goes there, but why VON. Why not VOM or VOR.
I just imagine myself sitting on a chair near a fireplace saying this sentence calmly only to loudly scream DER! or VOR! mid sentence.
vom is a contraction of von dem, i.e. "of the".
In standard German, we don't use the definite article with names or people -- we don't talk about "the Karl". (You may hear the definite article in informal language or in dialects, though, as in Der Hans ist der Bruder vom Karl. But that's not accepted on this course.)
vor is a preposition meaning "before" or "in front of". It's not a contraction of von der, in case you though that -- von der does not have a contraction in standard German. (In my colloquial speech, it does have one, but that's vonner, not vor.)
So it's just "the brother of Karl" der Bruder von Karl, not "the brother of the Karl" or "the brother in front of Karl".
sein (to be) is not a transitive verb that takes a direct object in the accusative case.
(Which is also why you can't turn it into the passive voice: "Karl's brother is been by Hans"(???).)
Instead, "to be" is a copula or linking verb that links a subject to a predicate that says something about the subject.
Such predicates are in the nominative case in German.
Same with werden (to become), e.g. er ist ein guter Vater geworden "he has become a good father".