Learn Hardcore Danish: Dit tøj er beskidt, fordi du løb udenfor. - Your clothes are dirty because you ran outside.

din is used with common-gender nouns: din bil (your car), din trøje (your sweater).
dit is used with neuter-gender nouns: dit hus (your house), dit barn (your child).

The word tøj is neuter, so you must say dit tøj, not din tøj.

Why is there no article before tøj? Why not et tøj?

Tøj is usually treated as an uncountable mass noun in Danish, like clothing in English. Uncountable nouns in Danish normally do not take an indefinite article:

tøj – clothes, clothing
vand – water
musik – music

If you want to say some clothes, you can say noget tøj, but et tøj is not used in normal Danish.

Why is the adjective beskidt not beskidt with -t, since tøj is neuter?

Adjectives behave differently depending on where they appear:

Before a noun, they agree in gender and number:
- et beskidt stykke tøj (a dirty piece of clothing) – neuter, so beskidt with -t
- en beskidt trøje (a dirty sweater) – common gender, no -t
- beskidte bukser (dirty trousers) – plural, -e
After a linking verb like er, adjectives stay in their base form, regardless of gender or number:
- Tøjet er beskidt.
- Trøjen er beskidt.
- Bukserne er beskidte.

In your sentence, beskidt is a predicative adjective after er, so it stays in the base form: er beskidt.

What is the difference between beskidt and snavset?

Both generally mean dirty, and in many everyday situations they are interchangeable:

Dit tøj er beskidt.
Dit tøj er snavset.

Nuances (not strict rules):

snavset often feels a bit more visibly filthy / grimy, with actual dirt or mud.
beskidt is very common and can also be used metaphorically:
- en beskidt løgn – a dirty lie
- beskidt humor – dirty humor

For your sentence about muddy clothes, either adjective is fine.

Why is there a comma before fordi?

Fordi introduces a subordinate clause (a dependent clause) that gives the reason.

In the traditional grammatical comma system in Danish, you must put a comma before most subordinate clauses, including fordi-clauses:

Dit tøj er beskidt, fordi du løb udenfor.

In a more modern pause comma system, the comma is more optional and depends on whether you want a pause. However, learners are usually taught to put a comma before fordi-clauses, so the comma here is perfectly standard.

Why is the word order fordi du løb udenfor and not fordi løb du udenfor?

Danish has different word order rules for main clauses and subordinate clauses:

In main clauses, the verb usually goes in second position (V2):
- Du løb udenfor.
- I dag løb du udenfor.
In subordinate clauses (introduced by words like fordi, at, hvis), the order is normally subject before verb:
- fordi du løb udenfor
- fordi han var træt
- hvis vi kommer for sent

So fordi du løb udenfor is correct; fordi løb du udenfor sounds wrong in standard Danish.

Could we also say Dit tøj blev beskidt, fordi du løb udenfor? What is the difference between er and blev here?

Yes, Dit tøj blev beskidt, fordi du løb udenfor is also correct, but the focus changes:

er beskidt – focuses on the current state: your clothes are dirty now.
blev beskidt – focuses on the change: your clothes got / became dirty at that moment.

So:

Dit tøj er beskidt, fordi du løb udenfor.
Emphasis: The result you see now.
Dit tøj blev beskidt, fordi du løb udenfor.
Emphasis: The moment or process of your clothes getting dirty.

Why do we use løb here and not har løbet?

Løb is the simple past (preterite) of løbe. Danish uses the simple past very often where English uses have run:

Du løb udenfor. – You ran outside.
Du har løbet udenfor. – You have run outside.

In your sentence, we are explaining a past cause of a present situation. Both are grammatically possible:

... fordi du løb udenfor.
Neutral statement of a past action.
... fordi du har løbet udenfor.
Slightly more focus on the action having (just) happened and its connection to now.

Many Danes would naturally choose løb here.

What are the main forms of the verb løbe?

The key forms are:

Infinitive: at løbe – to run
Present: løber – jeg løber (I run / am running)
Past (preterite): løb – jeg løb (I ran)
Past participle: (er) løbet – jeg er løbet (I have run / I ran)

Note that in compound tenses løbe typically uses er as the auxiliary, because it is a verb of motion:

Jeg er løbet en tur. – I have gone for a run.

What is the difference between udenfor and uden for?

They are written differently and used slightly differently:

udenfor (one word) is usually an adverb meaning outside / outdoors:
- Du løb udenfor. – You ran outside.
uden for (two words) is a preposition + adverb and usually takes an object:
- Du løb uden for huset. – You ran outside the house.
- Vi parkerede uden for byen. – We parked outside the town.

In your sentence there is no object after it, so the one-word udenfor is correct and natural.

Is udenfor here an adverb or a preposition, and what does it add to the sentence?

In fordi du løb udenfor, udenfor is an adverb. It tells you where the action løb happened:

du løb – you ran
du løb udenfor – you ran outside / outdoors

So it adds a location to explain why the clothes got dirty: running outside made them dirty.

How do you pronounce tøj, løb, and udenfor?

Approximate pronunciation (not exact IPA):

tøj – roughly like toy, but with a more open vowel, somewhere between tuhy and toy in English.
løb – the ø is like the vowel in French deux or German schön; the whole word is a bit like lerb without a strong r. Many learners hear it something like lurb.
udenfor – split as u-den-for:
- u like oo in food (a bit shorter)
- den like English den
- for with o like British English for, but shorter and more closed.

Listening to native audio and repeating is the best way to lock these in.