Χαμηλώνω τη μουσική γιατί η φίλη μου κοιμάται.

Because the verb ending already shows the subject.

Χαμηλώνω means I lower / I turn down.
The ending -ω tells you it is 1st person singular: I.

Greek often leaves out subject pronouns like εγώ when they are not needed. If you said Εγώ χαμηλώνω, it would sound more emphatic, like I’m the one turning it down.

Here, Χαμηλώνω means I turn down or literally I lower.

The verb χαμηλώνω can be used for things like:

• χαμηλώνω τη μουσική = I turn down the music
• χαμηλώνω τη φωνή μου = I lower my voice
• χαμηλώνω την ένταση = I reduce the volume/intensity

So in this sentence, it is the natural way to say I’m turning the music down.

Because μουσική is the direct object of the verb.

You are doing the action to the music, so Greek uses the accusative case:

• nominative: η μουσική = the music
• accusative: τη μουσική = the music

So:

• Η μουσική είναι δυνατή. = The music is loud.
• Χαμηλώνω τη μουσική. = I turn down the music.

Both are possible forms of the feminine accusative singular article.

The full form is την, but in everyday Greek the final -ν is often dropped before certain consonants. Since μουσική begins with μ, people commonly say and write:

• τη μουσική

You may also see την μουσική, especially in more careful or formal writing, but τη μουσική is completely normal.

Η φίλη μου means my friend.

Breakdown:

• η φίλη = the friend
• μου = my

In Greek, possessive words like μου, σου, του, της usually come after the noun:

• η φίλη μου = my friend
• το σπίτι μου = my house
• ο αδερφός της = her brother

That is the normal pattern.

Yes. Η φίλη is grammatically feminine and normally refers to a female friend.

Compare:

• ο φίλος μου = my male friend / my boyfriend
• η φίλη μου = my female friend / my girlfriend

Context tells you whether it means just friend or a romantic partner. In this sentence, the important thing for grammar is that the person is feminine, which matches the verb form.

Because the verb for sleep in Modern Greek is κοιμάμαι, which has middle/passive-style endings even though its meaning is active.

So:

• κοιμάμαι = I sleep / I am sleeping
• κοιμάται = he/she sleeps / is sleeping

This is very common in Greek. Some verbs look passive in form but are active in meaning. So η φίλη μου κοιμάται simply means my friend is sleeping.

It can mean either, depending on context.

Greek present tense often covers both:

• she sleeps
• she is sleeping

In this sentence, the most natural meaning is is sleeping, because that explains why the speaker is turning the music down right now.

So the sentence is naturally understood as:

• I’m turning down the music because my friend is sleeping.

Here, γιατί means because.

Greek γιατί can mean both:

• why?
• because

Context tells you which one it is.

Examples:

• Γιατί γελάς; = Why are you laughing?
• Γελάω γιατί είμαι χαρούμενος. = I’m laughing because I’m happy.

In your sentence, it clearly introduces the reason: because my friend is sleeping.

Greek word order is more flexible than English word order.

Starting with Χαμηλώνω is very natural. It puts the focus on the action:

• Χαμηλώνω τη μουσική γιατί η φίλη μου κοιμάται.

You could also say:

• Η φίλη μου κοιμάται, γι’ αυτό χαμηλώνω τη μουσική.
• Χαμηλώνω γιατί η φίλη μου κοιμάται.

The original sentence sounds normal and natural. Greek does not always need to begin with the subject the way English often does.

Grammatically, the present tense could describe either a general/habitual action or something happening now.

But in real context, this sentence strongly suggests a current situation:

• I’m turning down the music because my friend is sleeping.

If you wanted a more habitual meaning, the context would usually make that clear, for example:

• Πάντα χαμηλώνω τη μουσική όταν η φίλη μου κοιμάται.
  = I always turn down the music when my friend sleeps / is sleeping.

A few useful things:

• Χ in Χαμηλώνω is not like English h. It is a harsher sound, like the ch in German Bach or Scottish loch.
• η, ι, υ, ει, οι all sound like ee in Modern Greek. So φίλη and κοιμάται contain sounds English speakers may not expect from the spelling.
• αι is pronounced like e in bed, so κοιμάται sounds roughly like kee-MA-te.

You do not need perfect pronunciation immediately, but these are common things learners notice.

Yes, literally that is what it means, but in natural English the usual translation is I turn down the music.

This is a good example of where a literal translation is understandable, but a more idiomatic English translation sounds better. Greek often uses χαμηλώνω where English prefers turn down for volume.