Learn Hardcore German: Ein Zeuge ruft den Notarzt, und kurz danach kommt ein Krankenwagen mit lauter Sirene. - A witness calls the emergency doctor, and shortly afterwards an ambulance arrives with a loud siren.

Grammatically, einen Notarzt rufen is possible (accusative of ein Notarzt), but in practice den Notarzt rufen is a fixed expression in German meaning:

to call the emergency doctor service / to call 112 and ask for an emergency doctor

Using den here doesn’t usually refer to one specific, known doctor; it’s more like:

den Notarzt rufen ≈ call emergency medical services / call an emergency doctor

If you say einen Notarzt rufen, it sounds more like “call some emergency doctor” as an individual, and is much less idiomatic in this emergency‑services context. Native speakers strongly prefer den Notarzt rufen.

What is the difference between Notarzt and Krankenwagen?

They refer to different things:

der Notarzt
Literally emergency doctor – a specially trained doctor for emergencies.
It’s a person, not a vehicle.
der Krankenwagen
Literally sick-person vehicle – an ambulance.
It’s the vehicle that takes patients to hospital.

So in the sentence:

Ein Zeuge ruft den Notarzt – A witness calls for an emergency doctor.
… kommt ein Krankenwagen … – an ambulance arrives.

In everyday German, people sometimes say Krankenwagen rufen as well, but den Notarzt rufen is very common and focuses more on getting a doctor.

Why is there a comma before und in ..., und kurz danach kommt ein Krankenwagen ...?

Because there are two full main clauses:

Ein Zeuge ruft den Notarzt
kurz danach kommt ein Krankenwagen mit lauter Sirene

In modern standard German, when und joins two independent main clauses, the comma is optional:

Ein Zeuge ruft den Notarzt, und kurz danach kommt ein Krankenwagen … ✔
Ein Zeuge ruft den Notarzt und kurz danach kommt ein Krankenwagen … ✔

The comma is often preferred because:

The subjects differ (ein Zeuge vs. ein Krankenwagen),
The clauses are not very short.

So the comma helps readability, but leaving it out would still be correct.

Why is it kurz danach kommt ein Krankenwagen and not kurz danach ein Krankenwagen kommt or ein Krankenwagen kommt kurz danach?

German main clauses follow the verb‑second rule:

The finite verb (here: kommt) must be in second position in the clause.

Position 1 can be:

the subject, or
some other element like a time phrase.

In your sentence:

Position 1: kurz danach
Position 2: kommt (finite verb)
Then: ein Krankenwagen mit lauter Sirene

So kurz danach kommt ein Krankenwagen … is the standard word order.

Alternative that also respects verb‑second:

Ein Krankenwagen kommt kurz danach.

What you cannot do in a main clause is:

✗ kurz danach ein Krankenwagen kommt … (verb in third position)

That would only be possible if it were a subordinate clause, e.g.:

…, dass kurz danach ein Krankenwagen kommt.

What exactly does kurz danach mean, and how is it different from dann or danach alone?

danach = after that / subsequently
Refers to a point in time following something previously mentioned.
dann = then
More general sequence marker, sometimes less precise than danach.
kurz = short(ly) in a time sense.

So kurz danach literally means:

shortly after that / soon after(wards)

It emphasises that only a short time passes between the call and the arrival of the ambulance.

Compare:

Danach kommt ein Krankenwagen. – After that an ambulance comes (neutral about how long).
Kurz danach kommt ein Krankenwagen. – Very soon after that, an ambulance comes.

You can also hear kurz darauf with the same meaning.

Why is it mit lauter Sirene and not mit laute Sirene?

Because mit always takes the dative case, and Sirene is feminine.

For a feminine noun without an article in the dative, the adjective takes strong declension:

Dative feminine, no article: adjective ending ‑er

So:

mit lauter Sirene
= with loud siren / with its siren blaring

If you add an article, the ending changes:

mit einer lauten Sirene – with a loud siren
(Dative feminine, with article → adjective ending ‑en)

Both are grammatically correct, but mit lauter Sirene is a very common idiomatic pattern, like:

mit lauter Musik – with loud music
mit hoher Geschwindigkeit – at high speed

Does lauter here mean “louder” (the comparative of laut) or just “loud”?

Here it means simply “loud”, not “louder”.

lauter can be:

The comparative of laut:
- Die Sirene ist lauter als vorher. – The siren is louder than before.
A dative feminine strong adjective ending (as in your sentence), where the ending ‑er does not mark comparison, but case/gender:
- mit lauter Sirene – with loud siren (dative feminine, no article)
- mit lauter Musik – with loud music

You can tell it’s not a comparative because:

There is no comparison in the sentence (no als, no “than …”), and
It’s followed directly by a noun and governed by mit (which forces dative), so ‑er is the normal strong adjective ending here.

Semantically it just means the siren is (very) loud / actively sounding.

Why is there no article in mit lauter Sirene? Could we say mit der lauten Sirene?

Yes, mit der lauten Sirene is grammatically fine, but it slightly changes the nuance.

mit lauter Sirene
- No article, strong adjective: lauter
- Feels idiomatic and more like a manner description:
  with its siren going / blaring
- Focus on the state/activity (the ambulance is driving with siren on).
mit der lauten Sirene
- With article + adjective: dative feminine → der lauten Sirene
- Sounds a bit more concrete, as if you were referring to a particular siren that is already known in the context.
- Slightly heavier and less “formulaic”.

In everyday descriptions of emergency vehicles, the bare noun pattern is very common:

mit Blaulicht und Sirene – with blue light and siren
mit lauter Sirene – with loud siren

Could we say Ein Zeuge ruft den Krankenwagen instead of den Notarzt?

Yes, Ein Zeuge ruft den Krankenwagen is grammatically correct and understandable:

den Krankenwagen rufen – to call an ambulance

However, there are nuances:

den Notarzt rufen
Focuses on calling the emergency doctor service; fixed phrase; very common in German.
den Krankenwagen rufen
Focuses more on the vehicle that should come.

In real life, both essentially mean “call emergency services so that medical help comes,” but stylistically den Notarzt rufen is often the more idiomatic standard expression, especially in news reports or formal description of emergencies.

What are the genders of Zeuge, Notarzt, Krankenwagen, and Sirene, and how do they show up in this sentence?

The genders are:

der Zeuge – masculine
der Notarzt – masculine
der Krankenwagen – masculine
die Sirene – feminine

In the sentence:

Ein Zeuge – nominative singular masculine, indefinite article
- Subject of the first clause.
- Masculine nominative: ein.
den Notarzt – accusative singular masculine, definite article
- Direct object of ruft.
- Masculine accusative: den.
ein Krankenwagen – nominative singular masculine, indefinite article
- Subject of the second clause.
- Masculine nominative: again ein.
mit lauter Sirene – dative singular feminine, no article
- Object of mit (which always takes dative).
- Feminine dative with no article → adjective ending ‑er: lauter.

Knowing the gender lets you pick the correct article/adjective endings.

Why are Zeuge, Notarzt, Krankenwagen, and Sirene capitalized?

Because in German, all nouns are capitalized, regardless of their position in the sentence:

Zeuge, Notarzt, Krankenwagen, Sirene → all nouns → all capitalized.

Additionally:

Ein at the very start is capitalized because it is the first word of the sentence.
Words like ruft, kommt, kurz, danach, mit, lauter are not nouns, so they stay lowercase.

So capitalization here is simply following the regular rule: every noun, always capitalized.