Learn Hardcore Danish: Da vi kom til perronen, var toget allerede kørt. - When we arrived at the platform, the train had already left.

Danish main clauses are V2 (the finite verb must be in second position). The fronted subordinate clause (Da vi kom til perronen) occupies the first slot, so the finite verb (var) has to come next, before the subject (toget): …, var toget allerede kørt. If the main clause stands alone, you would say Toget var allerede kørt (subject in first position, verb in second).

What’s the difference between da and når, and which one fits here?

Use da for a single, specific time in the past (“when” referring to a past event). Use når for habitual/repeated times or general future (“whenever/when”). Here it’s one past event, so da is correct.

Is var kørt a passive (“was driven”)? It looks like it.

No. Var kørt here is the past perfect (plusquamperfect) formed with være + past participle for an intransitive motion verb. It means “had left/was gone (by departure).” A real passive would be var blevet kørt (“had been driven [by someone]”), which is a different meaning.

Why do we use være (be) and not have to form the perfect here?

A set of intransitive verbs of motion or change of state use være as auxiliary in the perfect tenses in Danish (e.g., gå, komme, falde, dø, køre in the sense “leave”). So: Toget er/var kørt = “The train has/had left.”

Could I say havde kørt instead of var kørt?

Not with this meaning. Havde kørt means “had driven/operated/run” (activity), not “had left.” Examples:

Togføreren havde kørt toget = “The driver had driven the train.”
Toget havde kørt i to timer = “The train had been running for two hours.” Departure is expressed with er/var kørt (or gået, see below).

Can I use gå instead: Toget var allerede gået?

Yes. With public transport, gå is very common for “depart”: Toget går kl. 8; Toget var gået = “The train had left.” Both var kørt and var gået are idiomatic.

Where should allerede go? Could I put it elsewhere?

Neutral placement is after the subject and before non-finite verb material:

After a fronted clause: …, var toget allerede kørt.
As a standalone main clause: Toget var allerede kørt. Fronting Allerede for emphasis is also possible: Allerede da vi kom til perronen, var toget kørt. Avoid placing allerede between the finite verb and the subject in neutral word order.

Why til perronen and not på perronen?

Til marks movement toward a place (“to/at” as a goal): kom til perronen = “came (arrived) at the platform.” På is used for location on a surface/place: var på perronen = “were on the platform.” If you want to emphasize moving onto the platform area, you can also say kom ud på perronen.

Why is it perronen with the -en ending?

Danish marks definiteness with a suffix. Perron = “platform,” perronen = “the platform.” The sentence refers to a specific platform (understood from context), so the definite form is natural. If it were non-specific, you might see en perron (“a platform”).

Could I say kom på perronen?

Colloquially you’ll hear it, but kom til perronen (arrived at) or kom ud på perronen (came out onto) are more idiomatic. Use på mainly for static location or with a verb that implies onto-ness (ud på).

Is kom just the past tense of komme? What about ankom?

Yes, kom is the preterite of komme. Ankom(me) is more formal/official (“arrive”), commonly used with larger destinations: ankomme til stationen/lufthavnen. You could say Da vi ankom til perronen, but kom til perronen is more everyday.

Do I need the comma after the first clause?

Yes. In standard Danish punctuation you put a comma after a fronted subordinate clause: Da vi kom til perronen, var … This separates the subordinate clause from the main clause.

Can I swap the clause order?

Yes: Toget var allerede kørt, da vi kom til perronen. The meaning is the same. Note the V2 word order remains in the main clause (Toget in first position, var in second).

Does kom til ever mean “ended up (accidentally)” here?

Not here. Kom til + noun means “came to (a place).” The “accidentally/ended up” meaning requires kom til at + infinitive (e.g., Jeg kom til at grine = “I ended up laughing / I accidentally laughed”).

What form is kørt, and how is it used in other tenses?

Kørt is the past participle of køre. Common combinations:

er kørt = present perfect (“has left”/“has driven” depending on context)
var kørt = past perfect (“had left”)
With have: har/ havde kørt = “has/had driven/been running” (activity), not departure.