Cfrgtkky

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?

Personally, I'm inclined to think that the first version (without second comma) is more natural. Grammatically, though, both versions are possible! The question to decide is whether »aber keinen Tee« is indeed functioning as a parenthetical, as you say. Thus the Duden online grammar says:

Bei den Konjunktionen aber, doch, jedoch, sondern lässt sich nicht immer zweifelsfrei entscheiden, ob sie eine Reihung oder einen Zusatz einleiten. In diesen Fällen ist das schließende Komma freigestellt.

• Sie waren arm, aber nicht unglücklich[,] und hatten viele Freunde.


• Die meisten Eltern, jedoch auch einige Schüler[,] waren gegen die Klassenfahrt.

(https://www.duden.de/sprachwissen/rechtschreibregeln/komma, end of rule D113)

This is saying sometimes a clause is ambiguous between being a »Reihung« (sequence, enumeration) and a »Zusatz« (parenthetical), in which cases the second comma is facultative. Their second example seems to be close to your sentence:

Die meisten Eltern, jedoch auch einige Schüler[,] waren gegen die Klassenfahrt.

Most parents, but also some students[,] have been opposed to the school trip.

Final note: The reason why I find the first version more natural is that it feels like an enumeration to me. After all, you can add many options, and it wouldn't seem to alter the construction:

Ich kann dir Kaffee, Limonade und Wasser, aber weder Tee noch heiße Schokolade anbieten.

I tend to idealize this kind of comma as that of enumeration, and aber as adverb.

We say

Ich kann dir Kaffe und Tee machen.

Ich kann dir Kaffe, Tee und Kuchen machen.

Ich kann dir keinen Tee, aber Kaffe und Kuchen machen.

This has limited explanatory power, since Tee, keinen Kaffee, Kuchen und Kekse is somewhat of a mixed bag, and aber works on the syntactic level to create context, that then must also be closed. I mean, Kaffe und Kuchen for example can mean a single entity, like tea time, but Ich kann dir Kaffee, aber keinen Tee und Kuchen implies keinen Tee und Kuchen were a combination, but that's nonesense, as it would reduce to just Kuchen.

Nevertheless, since written language is sequential, a list analogy is as close to the bare structure as it can get, and parallel dependencies are an after thought.

The last example would often be written as

Ich kann dir Tee--aber keinen Kaffe--und dazu Kuchen machen.

to highlight the different scope, but it might just use commas instead of dashes, and then you are pretty close to your original example. We don't set the second comma, because aber keinen Tee is not a proper Halbsatz, since it is lacking a verb.