Vi må skynde os hjem, for det begynder at regne.

Må is the present tense of måtte and is a modal verb.

In this sentence, it means something like:

• must
• have to
• need to

So Vi må skynde os hjem means that there is some necessity or urgency.

A useful point for learners:

• After a modal verb like må, Danish normally uses the next verb in the infinitive without at.

So:

• Vi må skynde os
• not Vi må at skynde os

Common modal verbs in Danish work like this:

• kan = can
• vil = will / want to
• skal = shall / must
• må = may / must

Because skynde sig is a very common reflexive verb in Danish, meaning to hurry.

That means the verb often goes together with a reflexive pronoun:

• jeg skynder mig = I hurry
• du skynder dig = you hurry
• han/hun skynder sig = he/she hurries
• vi skynder os = we hurry
• I skynder jer = you hurry
• de skynder sig = they hurry

So in your sentence:

• Vi må skynde os hjem

the os is not optional. It is part of the normal way of saying we must hurry.

Os is the reflexive/object form corresponding to vi.

So:

• vi = we
• os = us

In skynde os, the idea is literally something like hurry ourselves, though in natural English we just say hurry.

This is similar to how some verbs in other languages require a reflexive pronoun even when English does not.

Because in Danish, the reflexive pronoun usually follows the verb it belongs to.

So the basic pattern is:

• skynde sig
• skynde mig
• skynde os

With the modal verb included, the structure becomes:

• Vi må
  • skynde os
    • hjem

So må is the finite verb, and skynde os stays together as the infinitive phrase.

This is a very common learner question.

• hjem is used for movement toward home
• hjemme is used for being at home

So:

• Vi må skynde os hjem = we must hurry home
• Vi er hjemme = we are at home

A useful comparison:

• gå hjem = go home
• være hjemme = be at home

So in your sentence, since the idea is movement, hjem is correct.

Here for means because.

It links two main clauses:

• Vi må skynde os hjem
• for det begynder at regne

So it works like:

• We must hurry home, because it is starting to rain.

This is important because for can also mean for in other contexts, but here it is a conjunction.

For example:

• Jeg går nu, for jeg er træt. = I’m leaving now, because I’m tired.

Because for is a coordinating conjunction, not a subordinating one.

That means the clause after for keeps normal main-clause word order:

• det begynder at regne

Compare that with subordinating conjunctions like fordi, where learners often expect or learn different clause behavior.

In this sentence, after for, Danish still has:

• subject: det
• finite verb: begynder

So the order is straightforward.

Det here is a dummy subject or formal subject.

Weather expressions in Danish often use det, just like English uses it:

• Det regner = It’s raining
• Det sner = It’s snowing

So in:

• det begynder at regne

the det does not refer to a specific thing. It is just the grammatical subject needed for the sentence.

Because begynde is not a modal verb. It normally takes an infinitive with at.

So:

• begynder at regne = begins to rain
• prøver at sove = tries to sleep
• lærer at køre = learns to drive

Compare that with modal verbs, which usually do not take at:

• må gå
• kan komme
• vil spise

So in your sentence:

• må skynde os → no at
• begynder at regne → yes at

It can mean both, depending on context.

Regne can mean:

• to count / calculate
• to rain

In this sentence, because of det begynder at regne, it clearly means to rain.

This is normal in Danish:

• Jeg kan regne. = I can calculate.
• Det regner. = It is raining.

So learners need to rely on context.

The sentence contains two main clauses joined by for:

1. Vi må skynde os hjem
2. det begynder at regne

In Danish main clauses, the finite verb normally comes in the second position.

First clause:

• Vi = subject
• må = finite verb
• skynde os hjem = rest of the clause

Second clause:

• det = subject
• begynder = finite verb
• at regne = infinitive phrase

So the sentence is a good example of normal Danish main-clause word order.

In some contexts, yes, må can mean may or express permission. But here, the context strongly points to must / have to.

Because the next clause is:

• for det begynder at regne

there is a reason for urgency. So the natural reading is:

• We must hurry home

rather than:

• We may hurry home

Context is very important with må.