Learn Hardcore Greek: Μου αρέσει ο ρυθμός της ελληνικής γλώσσας όταν την ακούω στο ραδιόφωνο. - I like the rhythm of the Greek language when I hear it on the radio.

In English the subject is I, but in Greek the sentence starts with Μου αρέσει ο ρυθμός…. Who is the grammatical subject here, and why is it different?

In this Greek sentence, the grammatical subject is ο ρυθμός της ελληνικής γλώσσας (the rhythm of the Greek language), not I.

Μου = to me (indirect object, experiencer, genitive case)
αρέσει = is pleasing (3rd person singular of αρέσω)
ο ρυθμός = the rhythm (subject)

So the structure is closer to:

Μου αρέσει ο ρυθμός…
→ The rhythm … is pleasing to me.

English uses the pattern I like X (experiencer as subject), but Greek often uses the reverse: X pleases me (the thing liked is the subject, the experiencer is in the genitive with μου).

What exactly is μου here? Is it the same as εγώ?

Μου is a weak (clitic) personal pronoun in the genitive singular, meaning to me / my depending on context.

Here:

μου = to me (indirect object)
εγώ = I (strong subject pronoun, nominative)

You normally don’t say εγώ in this sentence unless you want to emphasize I, as in I (as opposed to others) like...:

Μου αρέσει ο ρυθμός… = I like the rhythm…
Εμένα μου αρέσει ο ρυθμός… = I (me), I like the rhythm… (contrastive/emphatic)

So μου is not a subject; it marks the person who experiences the liking.

Can I say αρέσει μου instead of μου αρέσει?

No, not in this kind of sentence.

Weak pronouns like μου, σου, του, της, μας, σας, τους normally go before the finite verb in statements and questions:

✅ Μου αρέσει ο ρυθμός…
❌ Αρέσει μου ο ρυθμός… (wrong in standard modern usage)

They come after the verb mainly in:

affirmative imperatives: Πες μου! (Tell me!)
some fixed expressions and non‑finite structures.

So here you must say Μου αρέσει, not Αρέσει μου.

Why is it ο ρυθμός and not η ρυθμός, and why do we need the article at all?

Gender
Ρυθμός is a masculine noun in Greek, so it takes the masculine article ο in the nominative singular:
- ο ρυθμός (masc. nom. sg.)
- του ρυθμού (masc. gen. sg.)
- τον ρυθμό (masc. acc. sg.)

So η ρυθμός would be grammatically wrong, because η is feminine.

Article use
In Greek, the definite article is used more often than in English, even with general or abstract nouns. Saying:

Μου αρέσει ο ρυθμός της ελληνικής γλώσσας…

is the natural way to say:

I like the rhythm of the Greek language… / I like the way Greek sounds…

Omitting the article (Μου αρέσει ρυθμός…) would sound ungrammatical here.

Why is it της ελληνικής γλώσσας and not η ελληνική γλώσσα?

Because here ελληνικής γλώσσας is in the genitive case, depending on ο ρυθμός.

ο ρυθμός της ελληνικής γλώσσας
literally: the rhythm of the Greek language

Breakdown:

της – feminine genitive singular article
ελληνικής – feminine genitive singular adjective (Greek)
γλώσσας – feminine genitive singular noun (language)

The genitive shows a relationship like:

ο ρυθμός του τραγουδιού = the rhythm of the song
ο ρυθμός της ελληνικής γλώσσας = the rhythm of the Greek language

If you said:

Μου αρέσει η ελληνική γλώσσα.

that would mean:

I like the Greek language.

That’s a different sentence: now η ελληνική γλώσσα is the subject itself, not a genitive phrase depending on ο ρυθμός.

Could I say Μου αρέσει η ελληνική γλώσσα instead? Does it mean the same thing?

You can say Μου αρέσει η ελληνική γλώσσα, but it does not mean the same thing.

Μου αρέσει η ελληνική γλώσσα.
→ I like the Greek language. (the language in general)
Μου αρέσει ο ρυθμός της ελληνικής γλώσσας όταν την ακούω στο ραδιόφωνο.
→ I like the rhythm of the Greek language when I hear it on the radio.
(you’re focusing specifically on the rhythm/sound of the language, not just liking the language as a whole)

Grammar-wise, both are correct; the meaning focus is different.

What does όταν do here, and why is the verb ακούω in the present tense?

Όταν is a conjunction meaning when (for time clauses).

The clause:

όταν την ακούω στο ραδιόφωνο

means something like:

when I listen to it on the radio / whenever I hear it on the radio

The present tense ακούω expresses a habitual or repeated action:

όταν την ακούω = whenever I (in general, habitually) hear it

If you said όταν την ακούσω, with the aorist subjunctive, you would refer more to a single event or eventuality:

Μου αρέσει όταν την ακούω στο ραδιόφωνο.
→ I like it when I (generally) hear it on the radio.
Θα χαρώ όταν την ακούσω στο ραδιόφωνο.
→ I will be glad when I (finally) hear it on the radio (one time, in the future).

So in your sentence, present ακούω matches the idea of a general habit.

What does την refer to in όταν την ακούω στο ραδιόφωνο? Why is it feminine?

Την here is a weak object pronoun in the accusative feminine singular.

It refers back to η ελληνική γλώσσα (which is implied from the earlier phrase της ελληνικής γλώσσας). Since γλώσσα is feminine:

η γλώσσα → την (as object pronoun)

So:

όταν την ακούω στο ραδιόφωνο
→ when I hear it (the language) on the radio

You don’t repeat τη(ν) ελληνική γλώσσα; you just replace it with the pronoun την.

If the antecedent were masculine or neuter, the pronoun would change accordingly (e.g. τον, το).

Could I move την after the verb and say όταν ακούω την?

No, not when την is a weak object pronoun.

With weak object pronouns, the normal pattern in statements and questions is:

pronoun before the finite verb: την ακούω

You cannot say:

❌ όταν ακούω την (wrong, if την is the pronoun)

But you can have την after the verb when it is the definite article of a noun:

όταν ακούω την ελληνική γλώσσα
(when I hear the Greek language)

Here την is not a pronoun but the article of γλώσσα, so ακούω την ελληνική γλώσσα is fine.

In your original sentence, την is a pronoun, so it must stay before ακούω: όταν την ακούω.

What exactly is στο ραδιόφωνο? Why στο?

Στο is the contraction of the preposition σε + the neuter article το:

σε
- το → στο

So:

στο ραδιόφωνο = σε το ραδιόφωνο literally
→ at/on the radio(-set)

In practice it means:

on the radio (as a medium of broadcast)

Greek regularly contracts σε with articles:

σε + τον → στον
σε + την → στη(ν)
σε + το → στο
σε + τους → στους
etc.

So στο ραδιόφωνο is the natural way to say on the radio.

Could I say στο ράδιο instead of στο ραδιόφωνο?

Yes, στο ράδιο is also used and understood.

ραδιόφωνο is the full word: radio receiver, radio set → on the radio
ράδιο is a shorter, more colloquial form.

Both:

Την ακούω στο ραδιόφωνο.
Την ακούω στο ράδιο.

can mean I hear it on the radio.
Στο ραδιόφωνο is a bit more neutral/standard; στο ράδιο slightly more informal.

Can you break down the forms της ελληνικής γλώσσας in terms of agreement?

Yes. All three words are feminine singular genitive:

η γλώσσα (fem. nom. sg.)
- genitive: της γλώσσας
ελληνική (fem. nom. sg. adjective)
- genitive: ελληνικής
article η (fem. nom. sg.)
- genitive: της

So:

της – feminine genitive singular article
ελληνικής – feminine genitive singular adjective
γλώσσας – feminine genitive singular noun

They all match in:

gender: feminine
number: singular
case: genitive

This agreement is required when you have article + adjective + noun.

What is the literal, word‑for‑word structure of the whole sentence?

The sentence:

Μου αρέσει ο ρυθμός της ελληνικής γλώσσας όταν την ακούω στο ραδιόφωνο.

can be glossed roughly as:

Μου – to‑me (genitive weak pronoun)
αρέσει – is‑pleasing
ο ρυθμός – the rhythm (subject)
της ελληνικής γλώσσας – of‑the Greek language
όταν – when
την – it‑her (fem. object pronoun, referring to the language)
ακούω – I‑hear
στο ραδιόφωνο – on‑the radio

Literal structure:

To me is‑pleasing the rhythm of‑the Greek language when it‑her I‑hear on‑the radio.

Natural English:

I like the rhythm of the Greek language when I hear it on the radio.