"Am I a grandfather?"
Translation:Bin ich ein Großvater?
"Bin ich ein Großvater?" is listed as the correct answer, so obviously I am missing something here. I incorrectly submitted "Bin ich einen Großvater." My (il)logic: "Ich" functions exclusively as a nominative pronoun, so it must be the subject of the sentence. Given this, "Großvater" must be in the accusative and thus must be preceded by "einen."
Where did I go wrong?
For a more technical answer: sein is what is called a copula. It is verb-like, but not really a transitive verb (a verb acting on an object). The English "to be" is very similar: we use it like a verb, but it really means something different than most verbs. Nothing is being acted upon or changed. The predicate of "to be" is not a direct object, since nothing is happening to it.
Here are a few good explanations of why a copula is different from transitive verbs: