Wrong on Nominative/Accusative?

[keehun]

I was asked to translate:

He is a teacher.

I gave it an answer "Er ist einen Lehrer" because I thought "a teacher" was the object and therefore accusative and therefore einen instead of ein.

The answer says that "a teacher" is nominative. Am I missing something?

[ketilk]

Yes, it's a predicative expression: http://en.wikipedia.org/wiki/Predicative_(adjectival_or_nominal)

I don't remember the rule, but when the verb "zu zein"(ich bin, du bist ...) is used to describe the subject it's nominative. There are a couple of other verbs as well.

As a general rule you can use nominative if it points to the subject ie: He is a teacher. and accusative when it's points to the verb

[keehun]

Thank you for the quick and helpful answer!

[Roxane]

Here, Lehrer is not an object because it is the same person as the subject. It's the same thing when you use the word "als", it will be always nominative afterwards