Learn Hardcore Swedish: Om dörren var låst, skulle katten stanna inne. - If the door were locked, the cat would stay inside.

Yes. Skulle is the past form of ska but is used to mark the conditional in modern Swedish. Skulle stanna corresponds to English “would stay.” It’s about modality, not past time. Compare:

Factual present: Om dörren är låst, stannar katten inne.
Hypothetical: Om dörren var/vore låst, skulle katten stanna inne.

Why is it var (past) in the if‑clause instead of är (present)?

Swedish typically uses the preterite in the om-clause together with skulle to express a hypothetical present/future condition. So Om dörren var låst, skulle… ≈ “If the door were locked, … would…”

Present factual rule: Om dörren är låst, stannar katten inne.
Past factual (habitual/real): Om dörren var låst, stannade katten inne.
Hypothetical: Om dörren var/vore låst, skulle katten stanna inne.

Can I use vore instead of var?

Yes. Vore (irrealis/subjunctive of vara) makes the condition feel more clearly hypothetical or counterfactual: Om dörren vore låst, skulle katten stanna inne. Both var and vore are correct; vore is a bit more formal/emphatic.

Why does skulle come before katten in the main clause?

Swedish main clauses follow the V2 rule: the finite verb must be in second position. The initial om‑clause counts as the first position, so the finite verb skulle must come next: …, skulle katten stanna inne.
Wrong: …, katten skulle stanna inne (violates V2).
If you start with the subject instead, you get: Katten skulle stanna inne om dörren var låst.

Is the comma after the om‑clause required?

Yes in standard Swedish: an initial subordinate clause is separated by a comma. Om dörren var låst, skulle…
If the om‑clause comes after the main clause, you normally omit the comma: Katten skulle stanna inne om dörren var låst.

What exactly is låst? Why not stängd?

Låst is the past participle of låsa (to lock), used adjectivally: locked.
Stängd means closed (not necessarily locked).

Agreement examples:

en låst dörr
ett låst fönster
låsta dörrar/fönster
den låsta dörren

Why are dörren and katten definite?

Dörren (the door) and katten (the cat) refer to specific, context‑known items (e.g., the household door and the family cat). That’s natural in Swedish for a concrete situation like this.
Note: Swedish can also use definite singular generically (e.g., Vargen är ett rovdjur), but here the reading is most likely specific.

What’s the difference between inne, in, and inomhus?

Inne = static location “inside/indoors.” Works with verbs of staying/being: stanna inne, vara inne.
In = directional “in(wards).” Use with motion into somewhere: gå in, släppa in.
Inomhus = “indoors,” a bit more formal/explicit than inne. Stanna inomhus is also fine.

Could I say stanna kvar inne or hålla sig inne?

Yes:

Stanna kvar inne emphasizes “remain” or “stay put.”
Hålla sig inne (“keep oneself indoors”) is idiomatic and common.
All are acceptable; stanna inne is the neutral default.

How does Om dörren var låst, skulle katten stanna inne differ from Om dörren var låst, stannade katten inne?

…skulle… = hypothetical outcome (“would stay”)—not asserting that it actually happened.
…stannade… = factual past (often habitual): whenever the door was locked (in reality), the cat stayed inside.

Can I put the om‑clause last?

Yes: Katten skulle stanna inne om dörren var låst.
No comma is needed in this order. The V2 rule still applies: with subject‑initial order, the finite verb (skulle) comes after the subject.

Can I add så after the om‑clause?

You can: Om dörren var låst, så skulle katten stanna inne.
Så is optional and adds a slight colloquial/contrastive feel. It’s often omitted in formal writing.

Can I say Om dörren skulle vara låst…?

Yes. Om dörren skulle vara låst… adds tentativeness (“should the door be locked,” “if it happens to be locked”). Common in instructions: Om dörren skulle vara låst, ring receptionen.

Where does negation (inte) go in sentences like this?

In subordinate clauses, inte comes before the finite verb: Om dörren inte var låst…
In main clauses, inte comes after the finite verb (V2): …, skulle katten inte stanna inne.
Full example: Om dörren inte var låst, skulle katten inte stanna inne.

Is om always “if”? It also means “about” and “whether,” right?

Om can mean:

“if” in conditionals (as here).
“whether” in indirect questions: Jag undrar om dörren är låst.
“about” as a preposition: Vi pratade om katten.
Context and structure make the meaning clear.

Any pronunciation tips for dörren, skulle, låst?

dörren: ö is a rounded vowel (like French “peu”), short here; stress on the first syllable.
skulle: sk is [sk] (not the “sh” sound), u is the Swedish front‑rounded vowel [ʉ]; two syllables: SKUL‑le.
låst: å is like a long “o” sound; final t is typically pronounced.