Explain a case problem I have please
In the sentence " Der Prasident ist mein Bruder" why is it "mein" and not "meinen" surely this is in the accusative case but it tells me it is in the nominative, why?
I am not a grammatician, but you can think of it this way: with the sentence "The President is my brother," you can switch both nouns and yield a very similar meaning: "My brother is the president." The verb "is" is not some action done to the noun following it.
For instance, if you said "The president killed my brother," then "my brother" would be in the accusative case because an action has been done to him, by the word in the nominative case, which is "the president." If you switch the nouns around to "My brother killed the president," it would mean a very, very different thing.
You have to use the nominative case after certain verbs such as "sein" (to be) and "werden" (to become). The word or phrase following these verbs is not an accusative object, but something called a "predicate noun". A predicate noun gives you more information about the subject of the sentence, i.e. in your case about the president.
These answers are very helpful - I think I'm starting to understand clearly the difference between nominative, accusative and dative. I just looked up these words on www.thefreedictionary.com, and it seems the word accusative comes from a mistranslation into latin of a greek word which means causative. And dative refers to the recipient of an action. It's all becoming clear to me now . . .