what is it?
German has two coordinating conjunctions that translate as but: aber and sondern. They are not interchangeable. Aber introduces a contrast or qualification — the first clause remains true. Sondern introduces a correction — it replaces something that was explicitly negated in the preceding clause. Without a negation (nicht, kein, nie, etc.) before it, sondern cannot be used.
when to use it
Use aber when both parts of the sentence can be true at the same time and you are adding a contrast or concession. No negation is required.
Use sondern when the first clause contains an explicit negation (nicht, kein, etc.) and the second clause corrects or replaces the negated element with something else.
Use nicht nur … sondern auch to say «not only X, but also Y» — adding a second element rather than replacing the first.
Quick test: can you remove the negation and still have a meaningful, true first clause? If yes, use aber. If the negation is essential because you are replacing the negated element, use sondern.
formation
Both conjunctions are coordinating: they join two main clauses (or two parallel phrases) and do not change word order. The verb stays in second position in each clause.
| pattern | example | meaning |
|---|---|---|
| … , aber … | Der Kurs ist schwer, aber interessant. | contrast — no negation needed |
| nicht X , sondern Y | Ich komme nicht aus Spanien, sondern aus Portugal. | correction — negated element replaced |
| nicht nur X , sondern auch Y | Sie spricht nicht nur Deutsch, sondern auch Türkisch. | addition — not only X, but also Y |
When sondern connects two full clauses (each with its own conjugated verb), both verbs remain in their normal positions. When it connects only parallel phrases (e.g. two prepositional phrases), the shared verb is not repeated.
examples in context
common pitfalls
Using aber after a negation that corrects.
Incorrect: Ich komme nicht aus Spanien, aber aus Portugal.
Correct: Ich komme nicht aus Spanien, sondern aus Portugal.
When nicht (or kein) explicitly negates an element and the second clause replaces that element, sondern is required. aber would imply that both clauses are true simultaneously, which contradicts the negation.
Using sondern without a preceding negation.
Incorrect: Der Kurs ist schwer, sondern interessant.
Correct: Der Kurs ist schwer, aber interessant.
sondern requires an explicit negation in the preceding clause. Without one, use aber.
A sentence can contain a negation and still use aber — if the second clause is a contrast rather than a direct replacement. Example: Er arbeitet nicht gern, aber er macht es. (He does not like working, but he does it.) Here the second clause does not replace «nicht gern» — it adds a contrasting fact. The test is whether the second clause substitutes the negated element or merely contrasts with the whole first clause.