We're (finally) studying coordinating conjunctions in German, and I came across the following sentence (which, according to the class, is grammatically correct):
Ich kann dir Kaffee, aber keinen Tee machen.
What troubles me about this sentence is that the part preceding "aber" is not a complete sentence. You couldn't say:
Ich kann dir Kaffee... (what? go on!)
In English, you would write:
I can make you coffee but not tea. (Comma before "but" is optional here.)
My inclination is to write:
Ich kann dir Kaffee, aber keinen Tee, machen.
Adding the second comma makes more sense to me, since "aber keinen Tee" is functioning as a parenthetical.
Am I missing something with respect to how German handles commas and coordinating conjunctions?