Learn Hardcore German: Unter keinen Umständen öffnest du die Tür, wenn die Klingel nachts klingelt. - Under no circumstances do you open the door when the bell rings at night.

Because of German’s verb-second (V2) rule in main clauses. One element goes in first position (here the fronted adverbial Unter keinen Umständen), and the conjugated verb must come second, so the subject follows the verb: Unter keinen Umständen öffnest du …. Without fronting, it would be the neutral Du öffnest …. This is not a question; it’s a normal V2 declarative with a fronted element.

Is this a double negative? Do I need nicht as well?

No. Unter keinen Umständen already expresses the negation. You do not add nicht here. If you want extra emphasis, you can intensify the same negation (e.g., unter gar keinen Umständen, auf keinen Fall, niemals), but you don’t stack a separate nicht on top of it unless you’re changing the scope (e.g., nicht nachts, meaning “not at night” specifically).

What case is unter keinen Umständen? Why keinen and the -n on Umständen?

It’s dative plural. The preposition unter takes the dative in this fixed expression, and in the dative plural:

the determiner kein becomes keinen
the noun adds -n: Umständen So: unter keinen Umständen. Other plural forms for comparison:
Nominative/Accusative: keine Umstände
Dative: keinen Umständen
Genitive: keiner Umstände

Could I also say Du öffnest die Tür unter keinen Umständen …? Is the meaning different?

Yes, that’s grammatical and means the same thing. Fronting the negative adverbial to the start (Unter keinen Umständen …) adds emphasis and a stricter, more warning-like tone. The unfronted version is neutral in word order but still just as prohibitive in content.

Does the sentence look like a question because the verb comes before du?

It may look that way at a glance, but a yes/no question would start with the verb and have nothing before it: Öffnest du die Tür? Here, there is a fronted phrase in first position: Unter keinen Umständen [1] öffnest [2] du [3] …. That makes it a declarative with emphasis, not a question.

Why is the verb at the end of the wenn-clause (… wenn die Klingel nachts klingelt)?

Because wenn introduces a subordinate clause, and in subordinate clauses the conjugated verb goes to the end: … wenn die Klingel nachts klingelt. In the main clause, German is V2; in subordinate clauses, it’s verb-final.

Why wenn and not falls?

wenn = “when/whenever/if” (for conditions that are expected, repeated, or generally conceivable)
falls = “in case (that)” (more hypothetical or precautionary) Here, the idea is “when(ever) the bell rings at night,” so wenn is the natural choice. Falls would sound more like a contingency plan: Falls es nachts klingelt, ….

Why nachts and not in der Nacht?

nachts means “at night (in general, habitually).” in der Nacht is more like “during the night,” often referring to a particular night or a time span. With a general rule/prohibition, nachts is the idiomatic pick. For extra emphasis you might hear mitten in der Nacht (“in the middle of the night”).

Is Die Klingel klingelt okay, or should it be Es klingelt?

Both are grammatical. Die Klingel klingelt is perfectly fine but can sound a bit tautological. In everyday German, the impersonal Es klingelt is very common and idiomatic. Many speakers would say: … wenn es nachts klingelt.

What’s the difference between die Tür öffnen and die Tür aufmachen?

öffnen is neutral/standard and works in formal and written contexts.
aufmachen is more colloquial and separable. Examples:
Main clause (V2): Unter keinen Umständen machst du die Tür auf.
Subordinate clause (verb-final): …, weil du die Tür nicht aufmachst.

Could I use an imperative instead, like Öffne unter keinen Umständen die Tür …?

Yes. That’s a direct command and sounds more overtly imperative:

Öffne unter keinen Umständen die Tür, … (du, singular)
Öffnet unter keinen Umständen die Tür, … (ihr, plural)
Öffnen Sie unter keinen Umständen die Tür, … (Sie, formal) Your original sentence is a strong directive phrased as a declarative with fronted negation, which can sound very firm while still being a statement.

Are there good alternatives to unter keinen Umständen?

Yes, common ones include:

auf keinen Fall (accusative after auf in this set phrase)
keinesfalls
niemals
um keinen Preis
unter gar keinen Umständen (intensified) All convey strong prohibition; register and rhythm vary slightly.

If I rewrite it with nicht, where does nicht go?

To negate the action as a whole, place nicht toward the clause end, before non-finite verb parts if present:

Du öffnest die Tür nicht, wenn es nachts klingelt. With a separable verb:
Du machst die Tür nicht auf, wenn es nachts klingelt. Be careful: moving nicht can change scope. For example, Du öffnest die Tür nachts nicht focuses on “not at night (but maybe at other times).”

Why is there a comma before wenn? Can I flip the clause order?

German requires commas before subordinate clauses. You can put the wenn-clause first or second:

Main first: Unter keinen Umständen öffnest du die Tür, wenn es nachts klingelt.
Sub first: Wenn es nachts klingelt, öffnest du die Tür unter keinen Umständen. Both are correct. Fronting Unter keinen Umständen keeps the strong prohibition front and center.

How would I say this formally to someone I address with Sie?

Two natural options:

Declarative directive (formal subject): Unter keinen Umständen öffnen Sie die Tür, wenn es nachts klingelt.
Imperative (most direct): Öffnen Sie unter keinen Umständen die Tür, wenn es nachts klingelt. The imperative is the standard way to issue a formal instruction.

Can I move nachts inside the wenn-clause?

Yes. All of these are fine, with slight shifts in emphasis:

… wenn die Klingel nachts klingelt
… wenn nachts die Klingel klingelt
… wenn es nachts klingelt The last is the most idiomatic for everyday speech.

Why not wann instead of wenn?

wann is used for direct and indirect questions about time (e.g., Wann klingelt die Klingel?, Ich weiß nicht, wann es klingelt.). wenn is the conjunction for “if/when(ever)” introducing a condition or repeated time.

Why present tense for what seems like a future event?

German often uses the present to talk about future/would-be situations when context makes the time clear, especially with wenn-clauses: Wenn es nachts klingelt, … Using werden here is usually unnecessary and can sound stiff.

Do I have to keep the subject pronoun du, or can I drop it?

Keep it. German generally requires explicit subject pronouns. Dropping the subject is not standard (unlike in Spanish/Italian). Only the imperative reliably omits the subject: Öffne …!