English has one word, "but," that covers two quite different logical jobs. German splits them: aber and sondern. Both are coordinating conjunctions, both translate as "but," and both can trip up English speakers who reach for aber by default. The distinction is sharp and learnable: sondern appears only when you negate something and then replace it with the truth; aber handles every other kind of contrast.
Both sit in position zero
First, a structural point that applies to both. aber and sondern are coordinating conjunctions (like und and oder), so they occupy "position zero" — they don't count as the first element of the clause and they don't trigger verb inversion. The word order after them is normal main-clause order.
Ich bin müde, aber ich kann noch nicht schlafen.
I'm tired, but I can't sleep yet.
Notice ich stays right after aber and the verb follows normally. There's also always a comma before aber and before sondern — German punctuation is non-negotiable here.
The core rule: sondern needs a negation it replaces
Use sondern only when both conditions hold:
- The first clause contains a negation (nicht, kein, nie, niemand…), and
- The second clause corrects or replaces the negated element with the contradicting truth.
This is the "not X, but rather Y" pattern. You're saying "forget X — the real answer is Y." English often signals this with "but rather" or "but instead."
Das ist nicht rot, sondern blau.
That's not red, but (rather) blue.
Er kommt nicht heute, sondern morgen.
He's not coming today, but tomorrow.
Ich möchte keinen Tee, sondern Kaffee.
I don't want tea, but coffee.
In each case the second element steps into the slot the first one was denied: blau replaces rot, morgen replaces heute, Kaffee replaces Tee. They are mutually exclusive alternatives in the same category.
aber: every other contrast
aber is the default "but." It introduces a contrast, qualification, or concession — and it does not replace a negated element. It's used everywhere sondern isn't, including, crucially, after a negation when there's no direct replacement.
Ordinary contrast between two compatible facts:
Die Wohnung ist klein, aber gemütlich.
The apartment is small but cozy.
Das Restaurant ist teuer, aber das Essen ist wirklich gut.
The restaurant is expensive, but the food is really good.
The subtle case: even after a negation, if the second clause adds something rather than replacing the negated item, you use aber:
Er ist nicht reich, aber zufrieden.
He isn't rich, but he's content.
Why aber here and not sondern? Because zufrieden (content) does not replace reich (rich) — being content is not the corrected alternative to being rich; they belong to different categories. The sentence isn't saying "not rich but rather content"; it's saying "not rich, yet nonetheless content." No replacement, so it's aber. Compare:
Sie wohnt nicht in Berlin, sondern in Hamburg.
She doesn't live in Berlin, but in Hamburg.
Here Hamburg replaces Berlin (same category: city of residence), so sondern is correct.
A decision table
| Clause 1 negated? | Clause 2 replaces the negated item? | Conjunction | Example |
|---|---|---|---|
| No | — | aber | klein, aber gemütlich |
| Yes | Yes (corrects it) | sondern | nicht rot, sondern blau |
| Yes | No (just adds/qualifies) | aber | nicht reich, aber zufrieden |
nicht nur … sondern auch
The most frequent fixed pattern with sondern is the correlative nicht nur … sondern auch ("not only … but also"). It fits the rule perfectly: nicht nur is the negation, and sondern auch adds the second member — except here it expands rather than rejects, which is the one idiomatic exception worth memorizing as a set phrase:
Sie spricht nicht nur Deutsch, sondern auch Französisch.
She speaks not only German but also French.
Das Konzert war nicht nur lang, sondern auch ziemlich langweilig.
The concert was not only long but also rather boring.
How this maps onto English
English "but" is doing two jobs at once, which is why the German split feels unintuitive:
- "but rather" / "but instead" / "but on the contrary" → sondern (correcting a negation)
- "but" / "yet" / "however" / "although" sense → aber (qualifying contrast)
A reliable mental translation: if you could insert "rather" or "instead" after the English "but," German wants sondern. If "but" reads as "yet/however," German wants aber.
Common Mistakes
The dominant error is using aber where sondern is required, because English "but" covers both:
❌ Er kommt nicht heute, aber morgen.
Incorrect — morgen replaces the negated heute, so sondern is required.
✅ Er kommt nicht heute, sondern morgen.
He's not coming today, but tomorrow.
The reverse error — using sondern for a plain contrast with no negation — is also common:
❌ Die Wohnung ist klein, sondern gemütlich.
Incorrect — there's no negation to correct, so it must be aber.
✅ Die Wohnung ist klein, aber gemütlich.
The apartment is small but cozy.
A subtler mistake: using sondern after a negation even when the second clause doesn't replace anything:
❌ Er ist nicht reich, sondern zufrieden.
Incorrect — content doesn't replace rich; nothing is corrected, so aber.
✅ Er ist nicht reich, aber zufrieden.
He isn't rich, but he's content.
Finally, forgetting the obligatory comma before either conjunction:
❌ Ich will keinen Tee sondern Kaffee.
Incorrect — a comma is required before sondern.
✅ Ich will keinen Tee, sondern Kaffee.
I don't want tea, but coffee.
Key Takeaways
- sondern only follows a negation (nicht/kein) and replaces the negated element with its contradicting alternative ("not X, but rather Y").
- aber is the default "but" for any other contrast — including after a negation when nothing is being replaced (nicht reich, aber zufrieden).
- Both are position-zero coordinating conjunctions (no verb inversion) and both require a comma before them.
- The set phrase nicht nur … sondern auch ("not only … but also") is the most common sondern construction.
- English "but" hides this split; insert "rather/instead" mentally — if it fits, use sondern.
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Start learning German→Related Topics
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- Coordinating Conjunctions (und, aber, oder, denn, sondern)A1 — The five coordinating conjunctions — und, aber, oder, denn, sondern — link two equal main clauses without touching the word order: the verb stays in second position in both.
- Negation, Correction (sondern), and doch as a Positive AnswerA2 — How 'sondern' corrects a negated statement and how 'doch' contradicts a negative — German's third answer word with no English equivalent.
- Two-Part (Correlative) ConjunctionsB2 — The paired connectors — entweder...oder, weder...noch, sowohl...als auch, nicht nur...sondern auch, je...desto — and their word-order surprises, including the unique verb-final je-clause.
- Negation: nicht and keinA1 — German's two main negators and their division of labour — kein negates nouns with an indefinite or no article, nicht negates everything else, and the choice hinges on the noun's article.
- Coordinating vs Subordinating Conjunctions and Word OrderB1 — The conjunction you choose dictates the word order: coordinating conjunctions leave V2 untouched, subordinating ones send the verb to the end — and 'denn' vs 'weil' proves it.