Learn Hardcore German: Der Lieferant ruft an, sobald er vor der Tür steht. - The delivery person calls as soon as he is at the door.

Because sobald introduces a subordinate clause. In German, subordinate clauses are always separated from the main clause by a comma. If the sobald-clause comes first, you also put a comma after it: Sobald er vor der Tür steht, ruft der Lieferant an.

Why does the verb go to the end in sobald er vor der Tür steht?

In subordinate clauses introduced by words like sobald, weil, dass, obwohl, the finite verb goes to the end. So in the main clause it’s verb-second (ruft), and in the sobald-clause it’s verb-final (steht).

Why is it ruft an and not anruft?

Anrufen is a separable-prefix verb. In a main clause, the prefix splits off and goes to the end: ruft an. In a subordinate clause, the prefix re-attaches and the whole verb goes to the end: …, sobald der Lieferant anruft. In the perfect tense, the past participle is angerufen.

Can I put the sobald clause first?

Yes. Both orders are correct:

Der Lieferant ruft an, sobald er vor der Tür steht.
Sobald er vor der Tür steht, ruft der Lieferant an. Only the main clause keeps verb-second; the sobald-clause keeps the verb at the end.

Why is the present tense used for a future event?

German commonly uses the present to talk about the near future when context makes the timing clear. Der Lieferant ruft an, sobald … naturally refers to a future call. You can use future as well (wird anrufen), but it’s not required.

Is sobald the same as wenn or als?

Not exactly:

sobald = as soon as; emphasizes immediate succession.
wenn = when/whenever/if; general condition or repeated event.
als = when (one-time event in the past). A near-synonym of sobald is sowie, more common in written style.

Why is it vor der Tür and not vor die Tür?

Vor is a two-way preposition:

With the dative (here: der Tür) it answers “Where?” (location, no movement).
With the accusative (die Tür) it answers “Where to?” (movement/direction). Since he is located in front of the door (not moving there), it’s dative: vor der Tür.

Why der if Tür is feminine?

Because it’s dative singular. Feminine nouns take der in the dative singular: die Tür (nom/acc) → der Tür (dat).

What’s the difference between vor der Tür and an der Tür?

vor der Tür = in front of the door (often implies outside).
an der Tür = at/by the door (right at the door, could be inside or outside, very close contact).
If you want to emphasize “outside the door,” vor der Tür is the safer choice.

Why steht and not ist?

Both can work. stehen paints the physical picture of someone standing there. sein is more general (“is at the door”). Note that vor der Tür stehen is also idiomatic for “to be imminent”: Der Winter steht vor der Tür.

Does anrufen need an object or a preposition?

To call a person: direct object in the accusative, no preposition: Ich rufe ihn/sie an.
To call an office/company/place: bei
- dative is common: Ich rufe bei der Firma an. Avoid “anrufen zu/auf”; those are incorrect.

Is ruft an about a phone call or shouting?

anrufen means “to call by phone.” rufen alone means “to call/shout.” If you mean the doorbell, use klingeln: Der Lieferant klingelt …

Who does er refer to? Could it be sie?

Er refers back to der Lieferant (a masculine noun). If you talk about a female delivery person, you’d use die Lieferantin … sobald sie vor der Tür steht. In gender-inclusive writing you might see formulations like die liefernde Person or der/die Lieferant(in).

How do I decline Lieferant?

It’s a weak (N-) masculine noun. Singular:

Nominative: der Lieferant
Accusative: den Lieferanten
Dative: dem Lieferanten
Genitive: des Lieferanten
Plural: die Lieferanten (all oblique cases add -en).

Can I replace vor der Tür with davor?

Yes, if “the door” is already clear from context: …, sobald er davor steht. Davor means “in front of it.”

How would this look in the past?

Simple past: Der Lieferant rief an, sobald er vor der Tür stand.
Word order rules stay the same: main clause verb-second; subordinate clause verb-final.

Is sobald always one word?

Yes, as a conjunction it’s one word: sobald. The two-word so bald only appears in comparisons like so bald wie möglich (“as soon as possible”).

Where does zu go with anrufen in an infinitive?

Between the prefix and the stem: anzurufen. Example: Er versucht, uns anzurufen, sobald er vor der Tür steht.